---
name: tile-installation
description: |
  Guides the user through tile installation from layout planning through grouting, covering substrate preparation, mortar selection, cutting techniques, and when to hire a professional. Produces a project plan with material list, time estimates, and step-by-step instructions.
  Use when the user asks about installing tile, tiling a floor or wall, choosing mortar or grout, tile layout planning, or whether a tile project is DIY-appropriate.
  Do NOT use for selecting flooring type (use flooring-selection instead), removing existing tile, or heated floor installation under tile.
license: Apache-2.0
metadata:
  author: foundry-skills
  version: "1.0.0"
  tags: "home-maintenance step-by-step planning"
  category: "home-household"
  subcategory: "home-maintenance"
  depends: ""
  disclaimer: "none"
  difficulty: "intermediate"
---
# Tile Installation

## When to Use

**Use this skill when:**
- User asks how to install tile on a floor, wall, backsplash, or tub surround -- any interior surface where tile is being set in mortar or adhesive
- User wants to plan a tile layout including starting point selection, pattern orientation, cut tile placement, and focal-wall alignment
- User needs help choosing the correct thin-set mortar, grout type, trowel size, or backer board product for their specific substrate and tile combination
- User asks for material quantity calculations -- tile square footage, mortar bags, grout pounds, backer board sheets
- User is deciding whether their specific tile project is within DIY capability or warrants hiring a professional tile setter
- User asks about grouting technique, grout joint width, spacer sizing, or grout sealing schedule
- User wants a day-by-day project schedule with cure-time windows built in

**Do NOT use when:**
- User is choosing between flooring types (hardwood vs. tile vs. LVP) -- use `flooring-selection` instead
- User wants to remove existing tile -- demolition involves different tools, substrate damage assessment, and disposal concerns outside this skill's scope
- User needs to install a radiant floor heating system under tile -- the low-voltage mat or hydronic loop installation requires its own skill; note that tiling OVER an already-installed mat is covered in Edge Cases here
- User is tiling an outdoor surface, patio, pool deck, or exterior wall -- freeze-thaw cycles, drainage slopes, and frost-resistant tile specifications are outside this skill
- User wants decorative tile design, pattern selection, or mosaic art -- those are design decisions, not installation procedure
- User needs to repair cracked grout or replace a single broken tile -- use a targeted repair skill
- User asks about tile underlayment for sound-dampening in multi-story buildings -- requires acoustic mat specifications beyond standard substrate prep

---

## Process

### Step 1: Assess Project Scope and DIY Suitability (15-30 minutes)

- Identify the surface type: bathroom floor, kitchen floor, shower wall, tub surround, kitchen backsplash, or laundry room. Each has different substrate requirements, waterproofing obligations, and complexity levels.
- Measure the area precisely: length × width in feet for rectangular rooms. For L-shaped rooms, break into rectangles and add together. Add 10% for cuts and waste, plus 5% reserved for future repairs -- total overage is 15%.
- Assess tile size and format. Tiles under 13×13 inches are beginner-appropriate. Tiles 15×15 to 24×24 require more precise substrate flatness and leveling clip systems. Tiles over 24×24 (large-format) are intermediate-to-advanced due to lippage risk and mortar coverage requirements.
- Evaluate the existing substrate before committing to a start date -- a failing substrate discovered mid-project doubles the timeline.
- Count the number of cuts required. Simple rectangular rooms with one toilet flange = minimal cuts. Rooms with curved walls, multiple penetrations, diagonal cuts, or custom niches multiply both time and skill requirements.

**DIY suitability decision framework:**

| Factor | DIY-Appropriate | Hire a Professional |
|---|---|---|
| Tile size | Up to 18×18 inches | 24×24 or larger on walls |
| Layout pattern | Grid (straight), simple offset | Herringbone, Versailles, diagonal in non-square room |
| Room shape | Rectangle, minimal obstacles | Many curves, angles, or L-shapes |
| Surface | Floor | Shower floor with custom pan, steam shower |
| Substrate condition | Sound, flat within 1/4" per 10 ft | Deflection, rot, structural bounce |
| Wet area? | Tub surround (manageable) | Full shower enclosure, first project |
| First tile project | Bathroom floor, backsplash | Any vertical wet area |

---

### Step 2: Prepare the Substrate (2-8 hours depending on condition)

Substrate preparation is the single most critical phase of tile installation. More tile failures originate from poor substrate prep than from any other cause. Never rush or skip any sub-step here.

**Concrete slab:**
- Clean with a degreaser; remove all paint, adhesive residue, and contaminants that would prevent mechanical bonding of thin-set.
- Check flatness with a 10-foot straightedge. The maximum allowable variation for tile is 1/4 inch over 10 feet for standard tile, and 1/8 inch over 10 feet for tiles 15 inches or longer in any direction.
- Fill low spots with floor-leveling compound (latex-modified, self-leveling is easiest). Allow 24 hours to cure. Sand or grind high spots -- an angle grinder with a diamond cup wheel works for minor humps.
- Check for active cracks. Hairline cracks under 1/16" wide can be filled with epoxy injection or crack-isolation membrane applied over the full slab surface. Cracks wider than 1/16" or that show movement require a crack-isolation membrane (uncoupling mat or sheet-applied membrane) over the entire floor.
- Test for moisture: tape a 16×16-inch plastic sheet to the slab with all edges sealed. Wait 24 hours. Condensation under the plastic indicates a moisture problem -- apply a moisture barrier or use epoxy thin-set rated for high-moisture substrates.

**Plywood subfloor:**
- Assess total subfloor thickness. The combined assembly (subfloor + backer board) must be at minimum 1-1/8 inches thick to resist deflection. Common assembly: 3/4-inch plywood subfloor + 1/2-inch cement backer board = 1-1/4 inches (good). Thin assemblies (5/8" + 1/4") are marginal -- reinforce by adding blocking between joists below.
- Check for bounce and deflection. Stand in the center of the room and jump lightly. Any noticeable floor movement will eventually crack grout joints. The industry standard is L/360 deflection limit (span in inches divided by 360 equals the maximum midpoint deflection in inches). If the floor moves noticeably, add blocking or sister joists before proceeding.
- Fasten any loose subfloor panels with 3-inch screws into joists every 6 inches along edges and 8 inches in the field. Squeaks indicate movement -- find the source and eliminate it.
- Install cement backer board (Durock, HardieBacker, or equivalent -- all are appropriate; differences are primarily in weight and cutting ease) with a 1/4-inch gap at all walls, a 1/8-inch gap between sheets, and a 1/2-inch offset from any subfloor seams below. Use 1-5/8-inch galvanized cement board screws every 6 inches along edges and 8 inches in the field. Trowel a thin layer of unmodified thin-set under each sheet before screwing -- this prevents hollow voids under the board.
- Tape all seams with 2-inch alkali-resistant fiberglass mesh tape embedded in a thin coat of unmodified thin-set. Feather smooth. This prevents crack transmission from the seam joints into the tile above.

**Existing tile as substrate:**
- Tile-over-tile is acceptable ONLY when the existing tile is fully bonded (test by tapping -- a hollow sound indicates debonding), flat within tolerance, and structurally sound. Verify the existing installation did not leave the floor at a height incompatible with adjacent flooring after adding a second tile layer.
- Scarify (scuff) the existing tile surface with a 60-grit diamond sanding pad or surface grinder to improve adhesion. The glazed surface of most tile has zero porosity -- without scarifying, thin-set will not bond reliably.
- Fill existing grout joints with a floor-leveling compound, screeding flush. Tiling over recessed grout joints creates a wavy surface in the new tile.

**Drywall and wall surfaces:**
- Standard drywall (gypsum) is acceptable for backsplashes and dry decorative wall tile only. It is never acceptable in wet areas.
- In wet areas (tub surrounds, shower walls, areas within 6 inches of a sink or tub edge), replace drywall with one of three substrate options: (1) cement board (heavy, excellent bond, requires mesh tape at seams), (2) glass-mat gypsum board (lighter, same code approval), or (3) closed-cell foam tile backer (Schluter KERDI-BOARD, Wedi Board -- these are also waterproof on their own surface without additional membrane, which simplifies wet area waterproofing significantly).
- Install cement board sheets with 1/4-inch gaps between sheets and between the board and the tub or shower base. Never let cement board contact standing water at the bottom -- this causes deterioration over years.

**Waterproofing for wet areas (mandatory):**
- For cement board substrates in showers and tub surrounds, apply a liquid waterproofing membrane (RedGard, LATICRETE Hydro Ban, or similar) in two coats. The first coat is red/purple when wet and turns uniformly pink when fully dry (approximately 1-2 hours in average conditions). Apply the second coat perpendicular to the first. The final dry color should be a uniform, unbroken pink -- any thin spots appear darker and need a third coat.
- Pay special attention to corners, seams, and screw holes -- apply membrane tape or pre-formed corner pieces embedded in the first coat before the second coat.
- Foam backer boards (KERDI-BOARD, Wedi) are self-waterproof on their face but require membrane tape with thin-set at all seams and corners.
- The shower floor -- the pan -- requires a pre-slope under the liner and a post-slope on top of the liner, both pitched at 1/4 inch per foot toward the drain. If the user has a mud-bed shower pan (mortar pan), that is a separate skill area. Foam shower pan systems (KERDI-SHOWER, Wedi Fundo) are the most DIY-accessible option and integrate waterproofing with the pre-formed slope.

---

### Step 3: Plan the Layout (30-60 minutes)

Poor layout planning creates two highly visible problems: narrow slivers of cut tile at walls (anything less than half a tile width looks unfinished and unprofessional) and cut tiles that are not centered on focal points (windows, tub, doorways, fireplaces).

**For floors:**
- Find the true center of the room by snapping chalk lines from the midpoints of opposite wall pairs. The intersection is your starting reference point, but it is rarely the actual starting point for tile placement.
- Dry-lay a row of tiles (with spacers) from the center point to each wall in both directions. Measure the cut tile that would result at each wall.
- If the cut tile at any wall would be less than half a tile wide, shift the chalk line by half a tile in that direction. This ensures all cuts at walls are at least half a tile.
- Look at the most visible wall from the room entrance. A cut tile less than 3/4 of a tile width at the wall directly opposite the doorway is aesthetically unacceptable even if it technically passes the "half tile" minimum. Adjust the layout grid to give that wall the most favorable cut.
- For straight-grid layouts, your working chalk lines should form a true 90-degree angle. Verify with a 3-4-5 triangle: measure 3 feet along one line and 4 feet along the other -- the diagonal between those two points should measure exactly 5 feet. This is critical in rooms where walls are not perfectly square (common in older homes).
- For diagonal (45-degree) layouts: snap the layout lines at 45 degrees across the room's diagonal midpoint. Diagonal layouts create significantly more cut tile (approximately 25-30% more waste than straight grid) and should be noted in material calculations.

**For walls:**
- Identify the focal wall -- the wall seen first upon entering (often the wall facing the doorway or the wall directly behind a freestanding tub or vanity).
- On the focal wall, find the center and plan tile to be symmetric about that centerline. A centered layout on the focal wall should take priority over perfect cuts at side walls.
- For tub surrounds: plan the layout so that cut tiles at the outside vertical corners of the surround are at least 3/4 of a tile wide. The back wall of the tub is the focal wall -- center the layout there.
- Check the height of the last full tile at the ceiling or top of the installation. If it would create a sliver less than 2 inches, shift the horizontal starting course up or down by half a tile.
- Start wall tile installation from the second course up from the floor (not the first course). The first course is typically a cut tile that accounts for the floor not being perfectly level. Establish a level horizontal reference line (laser level or 4-foot spirit level) for the bottom of the second full-tile course, then install a temporary wooden ledger board along that line to support the weight of tile while thin-set cures.

**Tile quantity calculation:**
- Square footage × 1.10 for straight grid layouts (10% waste for cuts)
- Square footage × 1.15 for offset/brick patterns (15% waste)
- Square footage × 1.20 to 1.25 for diagonal patterns (20-25% waste)
- Add 5% to the total for a repair reserve stored in the same dye lot
- Round up to the nearest full box -- you cannot order half a box, and dye lots change between production runs

---

### Step 4: Select Materials (15-30 minutes)

Material selection errors are irreversible once installation begins. A mismatch between thin-set and substrate, or between grout joint width and grout type, creates failures measured in months, not years.

**Thin-set mortar selection:**

| Tile and Substrate Combination | Correct Mortar |
|---|---|
| Ceramic tile on cement board or concrete | Standard unmodified thin-set (ANSI A118.1) |
| Porcelain tile on any substrate | Polymer-modified thin-set (ANSI A118.4) -- porcelain's low absorption requires polymer for bond |
| Any tile on plywood (over backer board) | Polymer-modified thin-set -- the polymer compensates for slight subfloor movement |
| Large-format tile (15" or longer in any direction) | Large-format tile (LFT) mortar (ANSI A118.4 with medium-bed designation) -- creates thicker mortar bed |
| Glass tile | White non-sagging medium-bed mortar (not gray -- gray shows through glass) |
| Natural stone (marble, travertine) | White non-sag polymer-modified -- gray stains light-colored stone |
| Tile over uncoupling membrane (Schluter DITRA) | Unmodified thin-set on both sides of the membrane -- DITRA manufacturer specs prohibit modified on membrane side in some configurations; verify the current spec sheet |
| Any tile in wet area | Use an ANSI A118.4 modified thin-set or better -- never standard unmodified thin-set in wet areas |

- **Never use mastic (organic adhesive) on floors or in wet areas.** Mastic re-emulsifies when it contacts sustained moisture and releases the tile bond. It is appropriate only for dry, vertical wall applications where all of the following are true: no steam, no direct water contact, no floor, and tile is 12×12 or smaller.
- Mortar coverage: one 50-pound bag of thin-set covers approximately 40-50 square feet at standard trowel depth. For large-format tile with back-buttering, reduce coverage estimate to 25-35 sqft per bag.
- Mix thin-set to "peanut butter" consistency: thick enough that ridges hold their shape when you comb the trowel, but wet enough to compress fully when tile is pressed in. After initial mixing, allow to slake (rest) for 5-10 minutes, then re-mix. Never add water after slaking.

**Trowel notch size selection:**

| Tile Size | Trowel Notch |
|---|---|
| Mosaic (up to 4×4) | 3/16" V-notch |
| Up to 8×8 | 1/4"×1/4" square notch |
| 10×10 to 13×13 | 1/4"×3/8" square notch |
| 15×15 to 20×20 | 3/8"×3/8" or 1/2"×1/2" square notch |
| 24×24 and larger | 1/2"×1/2" square notch + back-butter every tile |

The goal is minimum 80% mortar contact coverage for floors in dry areas, 95% minimum for all wet areas and all exterior applications (ANSI A108.5). Test by lifting a freshly set tile -- if the ridges have not collapsed to cover at least 80% of the tile back, increase trowel notch size or add back-buttering.

**Grout selection:**

| Grout Type | Joint Width Range | Best Use | Notes |
|---|---|---|---|
| Unsanded (non-sanded) | 1/16" to 1/8" | Wall tile, rectified tile, polished stone | Sanded grout scratches polished and honed surfaces |
| Sanded | 1/8" to 1/2" | All floor tile, most wall tile | Requires sealing (cement-based); dominant type for most projects |
| Premixed urethane grout (Fusion, SpectraLOCK SIMPLEGROUT) | 1/16" to 1/4" | Backsplashes, light-traffic areas | Stain-resistant without sealing; not for high-traffic floors |
| Epoxy (2-part or 3-part) | Any width | Commercial kitchens, showers, high-stain areas | Superior stain and chemical resistance; difficult to work with; sets fast |

- Grout quantity: one 10-pound bag of sanded grout covers approximately 40-50 sqft for 12×12 tile with 1/8-inch joints. Coverage decreases with smaller tile (more joint length per sqft) and increases with larger tile.
- Grout color: choose a grout color before purchasing tile if possible. Light grout with dark tile in high-traffic areas is a maintenance challenge -- grout will discolor. Grout color approximately 1-2 shades darker than the tile is the lowest-maintenance choice.

---

### Step 5: Install the Tile (varies -- 15-25 sqft/hour for a beginner, 35-50 sqft/hour for an experienced DIYer)

- Mix thin-set in a clean bucket using a 1/2-inch drill with a mixing paddle (not a paint mixer paddle -- the geometry is different). Mix for 3-4 minutes until fully uniform. Allow to slake 5-10 minutes. Re-mix 30 seconds. Do not add water after slaking -- the polymer chemistry has already activated.
- Work in sections of approximately 15-20 square feet at a time (beginners) or 25-35 square feet (experienced). Thin-set has an open time of 20-30 minutes in normal conditions (65-75°F); high temperatures (above 85°F) or direct sunlight dramatically shorten this to 10-15 minutes. Never spread more mortar than you can cover with tile before the surface skins over.
- Apply thin-set with the flat side of the notched trowel first, pressing firmly into the substrate, then comb with the notched edge held at a 45-degree angle to the surface. All ridges must be parallel -- this allows them to collapse evenly under the tile and ensures full coverage.
- Orient the trowel ridges perpendicular to the longest dimension of the tile. For rectangular tile, trowel ridges should run the short direction. This ensures full coverage when the ridges collapse under weight.
- Back-butter tiles 12 inches or longer: apply a thin skim coat of thin-set to the back of the tile using the flat edge of the trowel. This fills any manufacturing irregularities in the tile back and significantly improves mortar contact coverage.
- Set the tile with a slight twisting motion (approximately 1/8 turn) to collapse the mortar ridges. Press firmly and consistently -- do not just lay the tile flat without pressure. Beat-in with a rubber mallet and a beating block (a piece of 2×4 wrapped in carpet works) to ensure uniform seating.
- Check lippage (height difference between adjacent tile edges) after every few tiles. Use a straightedge across adjacent tiles -- lippage greater than 1/32 inch for rectified tile or 1/16 inch for non-rectified tile is noticeable and uncomfortable underfoot. Correct by pressing down high tiles, shimming low tiles, or adjusting the mortar bed while the thin-set is still workable (within 15-20 minutes of setting).
- Place tile spacers (cross-shaped or T-shaped) at all four-corner intersections. Common spacer sizes: 1/16 inch for rectified tile (tiles with precisely cut edges), 1/8 inch for most floor tile, 3/16 inch for a more rustic look or handmade tile with dimensional variation.
- Leveling clip systems (Tile Leveling System, RAIMONDI, or similar): for large-format tile (15 inches or longer), install a T-shaped clip under each tile edge at every joint, then thread a wedge through the clip base during setting. When thin-set cures, snap off the clip tabs with a rubber mallet. These systems dramatically reduce lippage on large-format installations and are highly recommended even for intermediate DIYers using those formats.
- Do not walk on freshly set tile for 24 hours minimum. If you must cross the area, lay a piece of plywood over multiple tiles to distribute weight. Stepping directly on a single tile before the thin-set has cured will tilt or sink it.
- After all tile is set, remove spacers within 1-2 hours while thin-set is still soft enough to not break them off with difficulty. Spacers left in grout joints prevent complete grout fill.

**Cutting techniques:**

| Cut Type | Tool | Notes |
|---|---|---|
| Straight cuts | Manual snap cutter (score-and-snap) | Fast and clean for ceramic; marginal on dense porcelain -- requires quality cutter |
| Straight cuts (porcelain or large format) | Wet saw (tile saw with diamond blade) | Most reliable for porcelain; required for tiles 16" or larger |
| Curved cuts around toilet flange, pipes | Angle grinder with dry-cut diamond blade or wet saw with multiple straight kerfs | Score the curve and nibble with tile nippers to finish |
| L-shaped cuts (around door jambs) | Wet saw with two intersecting cuts | Enter from each edge and stop at the corner -- do not cut through the corner |
| Notched or scalloped cuts | Wet saw with multiple passes, tile nippers, or oscillating tool with diamond blade | Nippers are slow but produce tight curves; oscillating tool is fast but rough |

- Always wear safety glasses and a dust mask (N95 or better) when dry-cutting tile. Crystalline silica dust from porcelain and stone is a serious respiratory hazard.
- Score the tile face side up on a snap cutter; cut with a wet saw with the face side up as well (the blade exits through the face side on a wet saw, which can chip -- some cutters prefer face-down on the wet saw to put any chipping on the back).
- Wet saws require water -- keep the water reservoir clean and the diamond blade properly cooled. A glazed or burned blade cuts poorly and wears rapidly.

---

### Step 6: Grout the Joints (1-2 hours per 50 sqft)

Grouting is time-sensitive. Working too large an area at once results in hardened grout that is nearly impossible to remove from tile surfaces without acid washing. Working too slowly results in grout smearing and dragging in partially set joints.

- Wait a minimum of 24 hours after setting the last tile before grouting. For large-format tile, 48 hours is preferable. The thin-set must be hard enough to resist the lateral pressure of the grout float without shifting tiles.
- Remove all spacers. Use a utility knife, grout saw, or oscillating tool to clear any thin-set that has squeezed up into the grout joints above the tile surface -- joints should be clean to at least 2/3 of the tile thickness depth. Thin-set in the joints prevents the grout from achieving the correct depth and will show as cracks later.
- Mix sanded grout to the consistency of thick peanut butter or wet concrete -- it should hold shape when scooped onto the trowel and not slump or run. Pre-wet the grout lines with a barely damp sponge just before application in very dry or hot conditions to prevent rapid moisture absorption from drying the grout too fast.
- Apply grout with a rubber grout float held at a 45-degree angle to the tile surface. Push grout diagonally across the joints (at 45 degrees to the tile grid) using firm pressure to pack the joints completely. Work in sections of 10-15 sqft.
- After packing the joints, hold the float at a steeper angle (60-70 degrees) and scrape excess grout off the tile surface with the edge of the float, moving diagonally to avoid pulling grout out of the joints. Remove as much excess as possible before washing -- this dramatically reduces the amount of haze cleanup later.
- Wait 15-20 minutes (in normal conditions) for the grout to firm up slightly -- it should resist a fingernail impression but not be rock-hard. This window varies with temperature and humidity.
- Begin the wash phase. Wet a large cellulose sponge in clean water and wring it to barely damp -- it should feel almost dry. Wipe the tile surface in wide circular motions to dissolve and remove grout from the tile faces. Rinse the sponge in clean water after every 2-3 passes. Change wash water frequently -- dirty water re-deposits a thin grout film over the tile.
- Do not press the sponge into the grout joints or you will pull grout out and create low, hollow-sounding joints. Wipe lightly across the joints, not along them.
- After the first wash pass, look at the tile surface in raking light (a work light held at a low angle works well). A white haze on the tile surface is normal -- this is a thin deposit of cement binder. Let it dry completely (1-2 hours), then buff off with a dry microfiber cloth. If the haze does not buff off, it has hardened and will require a diluted acid wash (vinegar solution or commercial grout haze remover) -- never let grout haze sit more than 24 hours without removing it.
- After the first wash pass on any section, go back and tool the joints with a damp sponge corner or a joint-striking tool to create a slightly concave grout joint surface. Flush-filled joints show dirt more visibly; slightly concave joints shed water and look more finished.
- Allow grout to cure 48-72 hours before applying sealer. In high-humidity environments (like a bathroom that is in use), wait the full 72 hours. Sealing before the grout is fully cured traps moisture inside and causes grout to powder and deteriorate.
- Apply grout sealer by saturating the grout joints with a penetrating silicone-based or fluoropolymer sealer, wiping excess off tile faces within 5 minutes before it dries. Apply two coats. Test sealed grout by placing a few drops of water on the surface -- it should bead. If it absorbs within 30 seconds, apply a third coat.

---

### Step 7: Finish and Final Details (1-2 hours)

- Install silicone caulk -- not grout -- at every change-of-plane joint. This means: the joint where the floor tile meets the wall tile (or baseboard), every inside corner in a shower or tub surround, the joint where the tile meets the tub deck or shower base, and at any expansion joints in large tile fields. Grout is a rigid material with zero flexibility -- it will crack at these joints within one or two seasonal thermal expansion cycles. Silicone flexes and seals permanently when applied correctly.
- Choose caulk color to match the grout color as closely as possible. Most major grout manufacturers offer matching caulk in their color lines (Mapei, LATICRETE, TEC all do this). The joint width should be 1/8 to 3/16 inch -- wider joints look unprofessional and narrow joints may not adequately bridge movement.
- Apply caulk by cutting the tube at a 45-degree angle for a 3/16-inch bead. Run a continuous bead, then tool immediately with a wet finger or a caulk tool. Use painter's tape on both sides of the joint for perfectly straight lines, removing the tape before the caulk skins (within 5-10 minutes).
- Install transition strips at doorways where tile meets a different flooring material. T-molding strips bridge two floors at the same height; reducer strips transition tile down to a lower-profile floor. Saddle thresholds are used at exterior doors. All are typically anchored with a track set in thin-set before grouting, then the top cap snaps or screws in after grout cures.
- Reinstall the toilet with a new wax ring (never reuse the old wax ring -- the compression set is permanent). If the tile raised the floor height, use a wax ring with a plastic horn extension, or stack two standard wax rings. Torque the closet bolts evenly to avoid cracking the toilet base.
- Reinstall any removed fixtures, supply stops, drain covers, and outlet covers.
- Allow 72 hours before exposing grout to standing water (first shower, first mopping). After that, normal use is fine.

---

## Output Format

```
## Tile Installation Plan: [Room/Surface Name]

### Project Summary
| Parameter          | Value                         |
|--------------------|-------------------------------|
| Surface            | [Floor / Wall / Backsplash / Tub Surround / Shower] |
| Total area         | [X] sqft                      |
| Tile size          | [e.g., 12×24 porcelain]       |
| Layout pattern     | [Grid / Brick offset / Diagonal / Herringbone] |
| Grout joint width  | [1/16" / 1/8" / 3/16"]        |
| Substrate          | [Concrete slab / Plywood + CBU / Existing tile / Drywall / Cement board] |
| Wet area?          | [Yes -- waterproofing required / No] |
| DIY assessment     | [Appropriate for first-time / Recommended with preparation / Hire a professional for X] |

---

### Red Flags to Resolve Before Starting
- [Substrate issue 1, e.g., "Subfloor deflection detected -- add blocking before proceeding"]
- [Any missing waterproofing requirement]
- [Any material incompatibility identified]

---

### Materials List
| Item                             | Specification / Type         | Quantity          | Estimated Cost     |
|----------------------------------|------------------------------|-------------------|--------------------|
| Tile                             | [Size, material, finish]     | [X sqft + [Y]% overage] | $[range]     |
| Cement backer board              | [1/4" or 1/2", brand]        | [X sheets (3×5 or 4×8)] | $[range]    |
| Backer board screws              | 1-5/8" galvanized            | [1-2 boxes]       | $[range]           |
| Alkali-resistant mesh tape       | 2" wide                      | [X rolls]         | $[range]           |
| Thin-set mortar                  | [Unmodified / Modified / LFT / White] | [X bags (50 lb)] | $[range] |
| Grout                            | [Sanded / Unsanded / Epoxy, color] | [X lbs]      | $[range]           |
| Tile spacers                     | [1/16" / 1/8" / 3/16"]       | [X bags]          | $[range]           |
| Waterproofing membrane (if wet)  | [RedGard / Hydro Ban / foam board] | [X gallons]  | $[range]           |
| Silicone caulk                   | [Color to match grout]       | [X tubes]         | $[range]           |
| Grout sealer                     | Penetrating silicone-based   | 1 bottle          | $[range]           |
| Transition strip (if applicable) | [T-molding / reducer, material] | [X linear ft] | $[range]           |
| Self-leveling compound (if needed)| [Brand]                     | [X bags]          | $[range]           |
| **Estimated Total Materials**    |                              |                   | **$[low--high]**   |

---

### Tool Requirements
| Tool                         | Purpose                                | Source (own / rent / buy) |
|------------------------------|----------------------------------------|---------------------------|
| Wet saw with diamond blade   | Straight and angled cuts on porcelain  | [Rent $35-$60/day or buy] |
| Manual snap tile cutter      | Straight cuts on ceramic               | [Buy $30-$80 or rent]     |
| Notched trowel ([size])      | Spreading and combing thin-set         | Buy ($8-$15)              |
| Rubber grout float           | Applying grout                         | Buy ($8-$15)              |
| Large cellulose sponges (2+) | Washing grout haze                     | Buy ($6-$12)              |
| Mixing drill + paddle        | Mixing mortar and grout                | [Own or rent]             |
| Chalk line                   | Layout reference lines                 | Buy ($5-$12)              |
| 4-foot level or laser level  | Checking flat, plumb, level            | Own or rent               |
| 10-foot straightedge         | Checking substrate flatness            | Rent or use a long board  |
| Rubber mallet + beating block| Seating tile without chipping          | Buy ($12-$20)             |
| Tile spacers                 | Uniform joint width                    | Buy ($4-$8/bag)           |
| Knee pads                    | Comfort for floor work                 | Buy ($15-$30)             |
| Safety glasses + N95 mask    | Protection during cutting              | Buy ($10-$20 combined)    |

---

### Time Estimate
| Phase                        | Duration                | Wait Before Next Phase    |
|------------------------------|-------------------------|---------------------------|
| Substrate prep               | [X] hours               | 24 hrs (if leveling compound used) |
| Backer board installation    | [X] hours               | None -- proceed to layout  |
| Layout planning (dry lay)    | [X] hours               | None                       |
| Tile setting                 | [X] hours               | 24 hrs cure (48 for large-format) |
| Spacer removal + joint clean | 1 hour                  | None                       |
| Grouting                     | [X] hours               | 48-72 hrs cure             |
| Sealing + caulking           | [X] hours               | 24 hrs before water exposure |
| Finishing (transitions, fixtures) | [X] hours          | None                       |
| **Total active time**        | **[X] hours**           |                            |
| **Total elapsed time**       | **[X] days minimum**    |                            |

---

### Day-by-Day Schedule
| Day | Tasks |
|-----|-------|
| Day 1 | [Substrate prep, backer board, waterproofing coat 1] |
| Day 2 | [Waterproofing coat 2, layout planning, dry lay, begin tile setting] |
| Day 3 | [Complete tile setting, remove spacers, clean joints] |
| Day 4 | [Cure day -- no work on tile] |
| Day 5 | [Grout, wash, caulk change-of-plane joints] |
| Day 6-7 | [Cure] |
| Day 7-8 | [Apply grout sealer, reinstall fixtures, install transitions] |

---

### Critical Checkpoints
- [ ] Substrate flatness verified within [tolerance] over 10 feet
- [ ] Subfloor deflection test passed
- [ ] Layout dry-laid -- no cuts narrower than half a tile at visible walls
- [ ] Starting chalk lines verified 90 degrees (3-4-5 check)
- [ ] Mortar coverage test passed (lift a tile and verify 80%+ coverage)
- [ ] All spacers removed before grouting
- [ ] Silicone caulk at all change-of-plane joints -- no grout
- [ ] Grout sealed after 48-72 hour cure
```

---

## Rules

1. **Never recommend mastic adhesive for floors or wet areas.** Mastic re-emulsifies when it contacts sustained moisture and releases the tile bond within months. Specify thin-set mortar (the correct ANSI grade) in all cases except dry, vertical wall tile in areas with zero moisture exposure.

2. **Always specify the correct thin-set grade for porcelain tile.** Porcelain has extremely low absorption (water absorption below 0.5%) -- standard unmodified thin-set does not form an adequate bond with porcelain's dense, near-impermeable surface. Always specify polymer-modified thin-set (ANSI A118.4 or higher) for any porcelain tile, regardless of substrate.

3. **Waterproofing in wet areas is non-negotiable and must be specified in explicit steps.** Do not describe it as optional, "recommended," or something to "consider." Water intrusion through tile in showers is the leading cause of structural damage and mold in bathrooms. Specify two full coats of liquid membrane with seam tape at all joints, or foam backer board with taped seams.

4. **Always back-butter tiles with any dimension of 12 inches or larger.** Back-buttering in addition to troweling the substrate is required to achieve the 80% (dry area) and 95% (wet area) mortar contact coverage required by ANSI A108.5. This rule applies to both floors and walls.

5. **Specify silicone caulk -- not grout -- at every change-of-plane joint.** Inside corners, floor-to-wall joints, tub deck joints, and expansion joints must receive flexible silicone caulk. Grout at these locations cracks within one thermal cycle. This is one of the most commonly skipped steps in DIY tile work and one of the most visible failures.

6. **Never allow grouting before a minimum 24-hour thin-set cure (48 hours for large-format).** The lateral pressure of applying grout with a rubber float is enough to shift tiles that are set in partially cured thin-set. Once grout is in the joints, there is no way to realign a displaced tile without removing all adjacent grout, softening the thin-set, and resetting.

7. **Include a substrate flatness check with the correct tolerance before recommending any tile.** Standard tile requires 1/4 inch variation over 10 feet. Tile with any dimension 15 inches or longer requires 1/8 inch over 10 feet. Recommending large-format tile without flagging this requirement leads to lippage that cannot be corrected after installation.

8. **Specify the correct trowel notch size for each tile size.** An undersized trowel notch is the single most common cause of hollow-sounding tiles and eventual tile delamination. A 1/4"×1/4" trowel used for 16×16 tile will produce severely inadequate coverage. Always state the specific trowel size for the tile size specified in the project.

9. **Always include the plywood subfloor deflection check (L/360 standard) before recommending tile.** Tile is a rigid material with zero tolerance for substrate flexing. A subfloor that passes for hardwood or LVP may still be too flexible for tile. Failure to flag a bouncy subfloor is the second-most-common cause of cracked grout joints in DIY projects.

10. **Never specify unsanded grout for joints wider than 1/8 inch.** Unsanded grout lacks the structural aggregate to bridge wider joints and will crack, shrink, and crumble. Conversely, never specify sanded grout for joints narrower than 1/8 inch on polished or honed stone -- the sand particles scratch the finish permanently.

---

## Edge Cases

**Large-format tile (24×24 inches or larger):**
Large-format tile magnifies every substrate imperfection. The substrate must be flat within 1/8 inch over 10 feet -- half the tolerance allowed for standard tile. Achieve this with a floor-leveling compound on concrete or a skim coat of self-leveling compound. Use LFT (large-format tile) mortar, which has a medium-bed consistency and does not shrink or sag under the weight of large tiles. Back-butter every tile using a flat trowel, then comb the floor. Use a tile leveling clip system (Raimondi, Perfect Level Master, or similar) -- place clips under every tile edge, thread wedges through the clips, and snap off tabs after curing. Do not attempt large-format tiles on walls without prior tile experience -- sagging during cure requires constant monitoring and adjustment. This is an intermediate-level project minimum.

**Tiling over existing vinyl or linoleum:**
Tiling directly over resilient flooring is possible if all three conditions are met: (1) the vinyl is firmly bonded with no lifting, bubbling, or soft spots, (2) the surface is smooth (cushioned/foam-backed vinyl is not acceptable -- it will flex under the rigid tile), and (3) the added height of tile plus thin-set is acceptable relative to adjacent floors and door clearances. Sand the vinyl surface with 60-grit to improve adhesion and apply a polymer-modified thin-set. Critical: if the vinyl was installed before 1986, it may contain asbestos in the backing or adhesive. Do not sand, scrape, cut, or disturb it. Either tile directly over it (tiling over an intact asbestos-containing floor is generally acceptable under most state and local codes -- verify first) or hire a licensed asbestos abatement contractor.

**Tile over uncoupling membrane (Schluter DITRA or equivalent):**
An uncoupling membrane is a dimpled polyethylene mat installed between the substrate and tile. It serves three functions: it decouples the tile assembly from substrate movement (protecting grout joints on problem subfloors), it allows the substrate to move slightly without transferring stress to the tile, and it provides a drainage plane and venting cavity. DITRA and similar membranes are appropriate over plywood, concrete, and even heated floors. Installation sequence: trowel unmodified thin-set onto the substrate, press the membrane (fleece-side down) into the thin-set, then trowel modified thin-set into the membrane's square dimples for tile bonding. DITRA changes the trowel geometry -- you fill the dimples rather than comb ridges. Follow the manufacturer's technical specifications precisely for mortar type on each side of the membrane, as these specifications have changed in product revisions.

**Shower niche installation:**
A recessed shower niche is one of the highest-risk areas for water intrusion if improperly constructed. Build the niche box from cement board (not drywall, not regular plywood) or use a prefabricated foam niche insert. Waterproof every interior surface of the niche -- the four walls, the back, and especially the bottom shelf -- with two full coats of liquid membrane, applying seam tape at all corners. The bottom shelf must slope a minimum of 1/4 inch toward the shower (not toward the wall) to drain rather than pool. Tile installation order: back wall first, then the two side walls, then the top (ceiling of niche), then the bottom shelf. The shelf front edge should have a bullnose tile or a stone profile as the finish piece. Do not grout the joint between the niche bottom and the shower wall -- use silicone caulk there as a change-of-plane joint.

**Tile height transition and door clearance:**
Adding tile to a floor raises the finished floor height by the total of: backer board thickness + thin-set bed thickness + tile thickness. A common assembly adds approximately 1-1/4 to 1-1/2 inches of total height. This can create problems with: (1) door clearances -- interior door bottoms may need to be trimmed (undercut with an oscillating tool or handsaw, with the door still hung, using a tile as a depth guide), (2) toilet flange height -- the flange must be at or up to 1/4 inch above the finished tile surface; if the new tile covers the flange, a flange extender must be installed before grouting, and (3) transition to adjacent rooms -- if the height difference exceeds 1/2 inch, a ramped reducer strip or a tapered transition must be installed for accessibility and to prevent a trip hazard.

**Temperature and humidity during installation:**
Thin-set and grout require temperatures between 50°F and 90°F during installation and for the first 24 hours of cure. Below 50°F, the polymer in modified thin-set does not cure properly and the mortar remains soft and crumbly. Above 90°F, or in direct sunlight on a bright day, the open time of thin-set drops below 10 minutes and grout dries too fast to wash properly. In cold conditions: heat the room to at least 60°F for 24 hours before and 48 hours after installation. In hot or dry conditions: mist the substrate lightly before spreading thin-set, work in smaller sections (10-12 sqft), and grout in the cooler part of the day. Never install tile outdoors or in an unheated garage in winter conditions.

**Grout efflorescence (white powdery staining after cure):**
Efflorescence appears when soluble salts migrate through the grout to the surface during curing, leaving a white or gray powdery residue. It is distinct from grout haze (which appears immediately after washing). Efflorescence typically appears 1-4 weeks after installation and is more common in wet environments, with high-alkalinity thin-sets, or when the substrate has moisture migrating through it. Treatment: allow the grout to fully cure (30+ days), then clean with a diluted acid-based efflorescence cleaner (phosphoric acid at 10-15% concentration), following the product safety instructions precisely. Seal promptly after cleaning. Prevention: use a cementitious grout with low water content, do not over-water during installation, and ensure the substrate is dry before tiling.

---

## Example

**Input:** "I want to tile my bathroom floor. It's about 50 square feet, L-shaped around a vanity. The subfloor is 3/4-inch plywood. I've done some home improvement projects but never tiled. I'm thinking 12×24 porcelain tiles in a brick offset pattern. There's a toilet I'd need to remove."

---

## Tile Installation Plan: Bathroom Floor (L-Shaped, 50 sqft)

### Project Summary
| Parameter          | Value                                                |
|--------------------|------------------------------------------------------|
| Surface            | Floor                                                |
| Total area         | 50 sqft                                              |
| Tile size          | 12×24 porcelain                                      |
| Layout pattern     | Brick offset (1/3 offset recommended over 1/2 for 12×24 to avoid lippage) |
| Grout joint width  | 1/8 inch (minimum recommended for rectified porcelain) |
| Substrate          | 3/4-inch plywood subfloor + 1/2-inch cement backer board |
| Wet area?          | No -- standard bathroom floor, no shower            |
| DIY assessment     | Manageable for a handy first-timer with preparation -- 12×24 format requires careful attention to flatness and back-buttering |

---

### Red Flags to Resolve Before Starting
- The 3/4-inch plywood alone is insufficient -- you must install 1/2-inch cement backer board (total 1-1/4 inches). Confirm the current floor height + 1-1/4 inches (backer board) + 1/4 inch (thin-set) + 3/8 inch (tile thickness) does not create an unacceptable transition to the hallway floor or catch the bathroom door.
- The L-shape creates more cut pieces than a rectangle -- budget 15% waste (not 10%) for the brick offset pattern in an L-shaped room. Factor in extra cuts around the vanity base and toilet flange.
- 12×24 porcelain requires polymer-modified thin-set -- standard thin-set will not bond adequately to the low-absorption porcelain surface.
- Check the plywood subfloor for deflection by pressing firmly and walking across it. Any bounce or squeaking must be fixed before tiling -- add 3-inch screws into joists every 6 inches, and add blocking if the floor still flexes.
- The toilet flange must be at the finished tile height or up to 1/4 inch above it. Measure the current flange height relative to the existing floor, then calculate whether the new tile assembly will cover the flange. If it will, order a closet flange extender before starting.

---

### Materials List
| Item                              | Specification                       | Quantity                   | Estimated Cost         |
|-----------------------------------|-------------------------------------|----------------------------|------------------------|
| Porcelain floor tile              | 12×24 rectified, your chosen color  | 58 sqft (50 sqft + 15%)    | $175-$580 (varies widely by grade) |
| Cement backer board               | 1/2-inch HardieBacker, 3×
