Five clauses carry most of the risk: substrate acceptance (who prepares it, what limits you accept), movement joints, client-supplied tiles, warranty scope and exclusions, and how a claim is made. AI drafts them well from your own numbers and site rules, but a solicitor should check the final wording.
The usual failure is an AI draft that sounds firm and says nothing: "industry standard flatness", "the Client accepts the substrate", "no liability for cracking". Each of those either contradicts what you do on site or tries to exclude your own workmanship. Feed the model your real limits and expect to rewrite every sentence that contains the word "any". Nothing here is legal advice, and this is not a template to download: it is how to get drafts worth editing.
What a substrate clause has to settle before day one
Most tile disputes trace back to the floor or wall, not the tile. A substrate clause earns its place when it answers five questions in writing before anyone mixes adhesive:
- Who supplies and prepares the substrate? Screed, backer board, plywood, existing tile, plaster: name it, and say who is responsible for its soundness. If another trade or the client's builder prepares it, say so.
- What do you check on arrival, and where is it recorded? Flatness, soundness and stability, dryness, cracks, contamination (sealers, paint, adhesive residue, curing compounds), falls to any drain, and the stiffness of timber floors. The record is a one-page form, shown later.
- What are the limits, as numbers? "Level" and "flat" are not measurable. "3 mm over 3 m under a straightedge" is.
- What happens when a reading fails? Written notice within a set time, with readings and photographs, and a choice: the client's builder corrects it, you correct it at a rate fixed in the contract, or the client signs to proceed at their own risk for a named area. A fourth option is to pause with an agreed delay.
- What about hidden conditions? When you lift an old floor and find rot, a crack or a layer of old adhesive, work stops for that area, you photograph it and the fix is a variation, not a surprise on the invoice.
One more sentence belongs here, and AI drafts tend to leave it out: you do not assess the structure. For a timber floor, the client or their builder confirms the frame is stiff enough for the tile chosen. The reason is practical. Deflection limits for substrates exist and are tighter for stone than for ceramic, and a tiler cannot certify a floor frame.
Numbers to write into the clause: flatness, deflection and joints
The figures below come from technical papers by a setting-material maker, one on subsurface tolerances and one on large-format tile, which summarise the tile industry's installation standard and handbook. I read them in early November 2026. Editions change, so treat the table as a starting point and write into your contract the figures from the data sheets for the tile and setting material you are actually using.
| Item | Figure to consider writing | Caveat |
|---|---|---|
| Flatness, tile with every edge under 15 in (380 mm) | 1/4 in in 10 ft (about 6 mm in 3 m), and no more than 1/16 in in 12 in (about 1.5 mm in 300 mm) | The straightedge method measures the gap under a 10 ft (3 m) straightedge laid on the surface |
| Flatness, tile with an edge of 15 in (380 mm) or more, and natural stone | 1/8 in in 10 ft (about 3 mm in 3 m), and no more than 1/16 in in 24 in (about 1.5 mm in 600 mm) | One of the papers uses 23 inches when it defines "large format" in its introduction, so write the tile size in the clause, not the label |
| Deflection of a timber-framed floor | No more than L/360 under live load for ceramic and porcelain; L/720 for natural stone | A structural question for the builder or engineer, not the tiler |
| Joint width with non-rectified tile | At least three times the tile's facial variation, never under 1/16 in | The tile maker's data gives the variation figure |
| Dryness of screed or concrete | Take the limit and test method from the adhesive or membrane data sheet | Left open on purpose: limits depend on the product |
| Movement joint spacing | Take it from the maker's guidance or the handbook detail you install to, then draw it | The drawn layout is what goes in the contract |
Where the substrate is out of tolerance, the maker's paper says it must be corrected with a patching compound or self-levelling underlayment, or ground to the correct tolerance. Cracked or suspended substrates are covered with a crack isolation membrane. Those are your correction routes, so name them in the clause and price them in a schedule.
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Buy nowAn 18 m² floor: readings, verdict and the variation price
Here is a worked example, with every figure illustrative. A kitchen and dining floor of 18 m² (about 194 square feet) is to be tiled with 600 x 1200 mm porcelain over a concrete slab. On day one the tiler lays a 3 m straightedge at six positions and records the largest gap under it:
| Position | Gap under 3 m straightedge | Verdict at 3 mm (edge of 380 mm or more) | Verdict at 6 mm (all edges under 380 mm) |
|---|---|---|---|
| 1, by the door | 2 mm | Within limit | Within limit |
| 2, kitchen run | 4 mm | Outside limit | Within limit |
| 3, centre | 5 mm | Outside limit | Within limit |
| 4, dining side | 3 mm | At the limit, within | Within limit |
| 5, patio doors | 7 mm | Outside limit | Outside limit |
| 6, hall edge | 2 mm | Within limit | Within limit |
The same floor gives three failures for the large tile and one for a small tile. That is why the clause names the tile size and the limit together. The contract's schedule sets self-levelling preparation at $22 per m² (illustrative). If the three failing positions represent about 11 m², the correction is 11 x $22 = $242. If the tiler judges the floor needs treating as one area, it is 18 x $22 = $396. Either way the figure is known before work starts, and the drying time is whatever the compound's data sheet says, so the programme moves by that amount.
The tiler sends the client the readings, photographs and variation V-01 for $242 on day one. If the client approves, the record says so. If the client declines, the clause lets them sign to proceed at their own risk for the 11 m², and the warranty excludes lippage and hollow areas in that zone. Compare that with the alternative: a complaint about uneven tile edges six weeks later, with no record of what the slab looked like.
For the wider subfloor and moisture picture beyond tile, can AI draft flooring contract clauses for subfloor and moisture covers wood, vinyl and carpet, and how small builders use AI to price variations and change orders shows how to price a variation like V-01.
Prompt: draft each clause from your own inputs
Give the model your decisions as facts, forbid it from adding standards or numbers, and ask it to list its own doubts. The doubts list is the most useful part.
You are drafting contract clauses for a tile installation business that works for household customers. Write in plain English, numbered, each clause under 120 words. Use ONLY the facts and numbers I give. Do not name any standard or quote any figure I have not supplied. Mark anything you had to assume with [CHECK].
My trade terms
- Work: porcelain floor tile, 600 x 1200 mm, about 18 m2, over a concrete slab
- I inspect the substrate on day one and record readings on a Substrate Acceptance Record
- Flatness limit I work to: 3 mm over 3 m for tiles with any edge of 380 mm or more
- Correction routes: self-levelling compound or grinding, priced per m2 in Schedule 3
- Client supplies the tile: [yes or no]
- Movement joints: layout drawn in Schedule 4, flexible sealant, visible
- Workmanship warranty: [12] months from completion; claims in writing within [14] days of noticing
- Notice period for a substrate problem: 1 working day
Draft clauses for: 1 substrate acceptance, 2 movement joints, 3 client-supplied tile, 4 warranty and exclusions.
Then list every place where my terms are unclear or two clauses could conflict.A typical illustrative response is four numbered clauses and a doubts list with items such as: who approves the correction if the client is away, whether the warranty runs from completion or from payment, whether "large format" means any edge over 380 mm, who pays for the extra drying day, and what "visible" means for a joint that is later tiled over. Answer each doubt in the prompt, run it again, and only then start editing. Keep the client's real name and address out of the prompt: the clauses do not need them, and a business plan with training off by default is the safer place for contract drafts anyway.
Four AI drafts and what each needed fixing
These are illustrative first drafts of the kind a model produces when the prompt is loose, with the problem and the repair.
| Clause | Typical first draft | What was wrong | Edited wording |
|---|---|---|---|
| Substrate | "The Client acknowledges that the substrate is suitable for tiling and is responsible for any defects caused by it." | Makes the client certify something they cannot judge. "Any" is too wide. No limits, notice or correction route. | "Before tiling, the Contractor checks the substrate against Schedule 2 (flatness 3 mm over 3 m, soundness, dryness, cleanliness) and records the readings. If a reading is outside a limit, the Contractor tells the Client in writing within 1 working day with readings and photographs, and offers the correction priced in Schedule 3. Tiling in that area starts after the Client approves the correction in writing or signs to proceed at their own risk." |
| Movement joints | "Movement joints will be provided where required by industry practice." | "Industry practice" names nothing and invites an argument about visible joints after the job. | "Movement joints are placed as shown on the layout in Schedule 4, filled with flexible sealant, not grout, and stay visible. The Client confirms they have seen the layout. Any change to it is a variation." |
| Client-supplied tile | "The Contractor is not liable for any defects in tiles supplied by the Client." | Silent on checking tile before laying. "Any defects" could be read as excluding workmanship. | "Tile supplied by the Client is outside the Contractor's warranty. Before laying, the Contractor inspects the boxes opened on site for visible faults and tells the Client of any found. Tile laid after that point is treated as accepted." |
| Warranty | "The Contractor warrants the work for 12 months and is not liable for cracking." | A blanket cracking exclusion would cover the tiler's own poor adhesive coverage. Period and claim steps are missing. | "For 12 months from completion the Contractor will repair or replace tiling that fails because of the Contractor's workmanship, if the Client reports it in writing within 14 days of noticing it. The warranty does not cover cracking or loose tiles caused by movement of the structure or substrate outside the Contractor's work." |
Movement joints: agree the layout before the tile is ordered
A movement joint is a gap filled with flexible sealant that lets tiling and substrate move without cracking. The maker's paper on large-format tile says expansion joints should not be bridged but carried through to the finished surface, and that large expanses need control joints. Clients hate finding that out after the tile is down, because the joint is visible and the grout lines they imagined are interrupted.
The fix is a drawn layout, not a sentence. Mark joints at the room perimeter, at changes of plane, and over any movement joint in the slab or frame, and add field joints where the maker or handbook detail says the area needs them. Attach the drawing as a schedule and have the client initial it before the tile is ordered. The clause then does three jobs: it points to the schedule, it says the joints stay visible and are sealant, not grout, and it makes any move a variation. Without the drawing, "visible joints" is a promise nobody has seen.
Ask the model to write the clause, then check one thing yourself: that the clause never says the joints are "required by industry standard" unless you name the detail you installed to. A vague claim of compliance is worse than none, because it invites someone to ask which standard.
Client-supplied tiles: who carries which risk
When the client buys the tile, three risks shift and the clause must say where each lands. First, visible faults: chips, shade differences between boxes, warped tiles. Second, the quantity ordered. Third, the tile's own performance, which is the maker's and seller's business, not yours.
A workable allocation has the client inspect the delivery and the tiler inspect boxes opened on site, tell the client of anything found, and treat tile laid after that as accepted. Warranty covers installation workmanship only. The client orders the agreed quantity and keeps spare tile from the same batch. Two quick sums show why the clause needs numbers:
- Quantity. For the 18 m² floor, say the contract sets an overage of 15 percent for cuts and future repairs (ask the supplier what it recommends for the tile size and layout; diagonal and herringbone patterns waste more). At 15 percent that is 20.7 m². A box of two 600 x 1200 mm tiles covers 1.44 m², so 15 boxes (21.6 m²) is the order. Put your figure in the contract and the client cannot be surprised by a short delivery halfway through a cut layout.
- Joint width. The papers say joint width with non-rectified tile should be at least three times the tile's facial variation. If the maker lists 1.5 mm variation, the minimum is 4.5 mm. A client who wants hairline 2 mm joints with that tile has a conflict to resolve before ordering, by choosing a rectified tile or accepting a wider joint. Put the agreed joint width in the schedule.
Add one more line to the clause: the tiler may stop and ask if the boxes show different shades or sizes, and the delay is the client's to bear. AI drafts often forget that you need permission to stop.
Warranty wording: scope, exclusions and how to claim
A tiling warranty should promise less than clients assume and more than a blanket exclusion allows. Draft it as a short list the client can read in a minute:
- What is covered. Your installation workmanship, such as loose tiles or hollow areas from poor adhesive coverage, for a period you state. The period is yours to choose; do not copy a number from a sample.
- When it starts. A defined date, such as completion or final payment, and the clause says which.
- What is excluded, specifically. Movement of the structure or substrate outside your work, leaks and failed sealant maintenance, impact or chemical damage, tile supplied by the client, and areas where the client signed to proceed over a substrate outside your limits.
- How to claim. In writing, with photographs, within a stated number of days of noticing, with access for inspection.
- The remedy. Repair or replacement at your choice, and a statement of whether any other remedy is excluded.
- What the maker covers. If the setting-material maker offers its own system warranty, say whose it is. One maker's paper says its extended warranty applies when its full system of products is used, so a mixed set of products may leave the client with only yours.
The last two lines are where a solicitor earns their fee. How far a contractor can limit liability to a household customer varies from place to place, and some promises cannot be excluded at all, so a clause that looks tidy can be unenforceable. A model will happily write "the Contractor accepts no liability whatsoever" because it sounds protective. Ask the solicitor to read the remedy and exclusion lines first, and give them the doubts list the AI produced, which saves their time and yours.
If you want a second set of examples for tidy warranty wording, a garage door repair contract with warranty wording drafted by AI shows the same scope-and-exclusion pattern for another trade, and a concrete contract template covering cracking and delay is worth reading if you tile over new slabs.
A one-page substrate acceptance record
The clause only works if the record exists. This is a blank version to adapt: fill it on day one, photograph the straightedge at each position, and email a copy to the client before you leave.
SUBSTRATE ACCEPTANCE RECORD
Date: ____ Room/area: ____ Tile: ____ (largest edge ____ mm)
Substrate type: ____ Prepared by: ____
Flatness (3 m straightedge, largest gap in mm)
Pos 1 ____ Pos 2 ____ Pos 3 ____ Pos 4 ____ Pos 5 ____ Pos 6 ____
Limit in contract: ____ mm over 3 m Positions outside limit: ____
Soundness and stability: ____
Dryness reading and method (limit from product data sheet): ____
Cracks (location, width): ____
Contamination (sealer, paint, residue): ____
Falls to drain / thresholds: ____
Photo numbers: ____
Decision
[ ] Accepted [ ] Accepted with variation V-__ ($____) [ ] Proceed at Client's risk, area: ____ [ ] Not accepted
Contractor: ____ Client (initials): ____ Copy emailed on: ____Ten checks on an AI-drafted contract before the solicitor sees it
- Every number matches your site-test sheet and your schedules, including the flatness limit, notice period and warranty period.
- No clause names a standard you do not actually install to.
- No absolute promises, such as "perfectly level", "will not crack" or "no liability whatsoever".
- "Substrate", "Works", "Completion" and "Variation" are defined once and used the same way throughout.
- The warranty period in the warranty clause matches any other mention, in the quote, on the invoice or in a schedule.
- Every clause that says "any" has been reread, and most have been narrowed.
- The substrate clause, the variation clause and the warranty exclusions agree with each other about proceeding at the client's risk.
- Notice periods are the same wherever they appear.
- The scope in the quote matches the scope the clauses refer to, including who supplies the tile.
- The doubts list the AI produced has an answer for every item, and the unanswered ones are marked for the solicitor.
Run the same list against every redraft. Models change wording between runs, and a clause you approved last month can come back slightly different if you regenerate it. Save the approved text in your own file and paste from it, rather than asking the model to recreate it.
Questions tilers ask about these clauses
Do I need a separate substrate report for every job?
A one-page acceptance record is usually enough: date, substrate type, flatness readings, dryness reading and method, cracks, photo numbers and the decision. Complete it on day one, photograph the straightedge readings, and send the client a copy the same day. It turns an argument about what the floor was like into a dated record.
Can I refuse to tile over a substrate I think is unsuitable?
In most cases a contractor can pause and give written notice, and the contract should say what happens next: the client corrects it, you correct it at an agreed rate, or the client signs to proceed at their own risk for a named area. Whether any of that is enforceable against a household customer is a question for your solicitor.
Should my warranty match the setting-material maker's?
Only if you are willing to stand behind it. Your warranty covers your workmanship, not the product. A setting-material maker may offer its own system warranty on different terms, and one maker's paper says its extended warranty applies when its full system of products is used. Never promise more than your own crew controls.
Will AI quote the right installation standard?
Do not rely on it. A model can quote an old edition, mix up local and international figures or invent a clause number that sounds right. Give it the limits you actually work to, taken from your tile and setting-material data sheets, and tell it not to name any standard you have not supplied.
Further reads
- Can AI Draft a Remodelling Contract Template in Plain English? — The whole remodelling contract in plain English, around your tile clauses.
- Painting Contract Template: Colour Approval and Change Orders With AI — Another finish trade, with approval and change-order wording to compare.
- Plumbing Change Orders: Four Worked Examples Drafted With AI — Worked change orders you can copy for extra substrate work.
- Roofing Change Orders for Rotten Decking: A Worked Example, AI-Drafted — Hidden-condition variations drafted with AI, for floors hiding surprises.
- AI Tools for Contracting Businesses: Subcontracts and Change Orders — Tools for subcontracts and change orders if you use sub-tilers.
- General Contractor AI: Turn Site Messages Into Change Orders — Turn site messages about extra work into written change orders.
- How to Quote a Tiling Job: Area, Waste and Prep Lines Checked With AI — A worked bathroom quote with area, waste, adhesive, grout, waterproofing and prep lines, plus the AI prompts that catch errors before the customer sees them.
- Workmanship Warranty: Exclusions to Draft With AI, Then a Solicitor Check — A bathroom fitter's warranty built from its own callback log: exclusions in plain words, claim steps, sample decisions and a solicitor-check pack.
- AI Tools and AI Development: The Complete 2026 Guide — the AI hub, including every tutorial in the AI-for-business series.
Sources: Custom Building Products technical papers on subsurface tolerances and large-format tile, which summarise the tile industry's installation standard and handbook, read in early November 2026. Moisture limits and joint spacing are left to the maker's data sheet on purpose.