Where Stone Jobs Lose Money: A Risk Guide for Contractors and Builders

  Where Stone Jobs Lose Money: A Risk Guide for Contractors and Builders

 

On paper, stone flooring and cladding look simple. There is a rate per square metre, a stone name and a fixing method, and the job goes to the lowest bidder. On site, margins disappear through what the tender left out: an unlevel slab, a missing fixing design, a stone that arrives thinner than assumed, a hoist that is booked for the whole week, or a floor that had to be relaid because another trade walked over it on day two.

This guide goes through the risks to look for before you price, while you mobilise, and during the work. It is written for contractors, subcontractors and builders’ project teams.

1. Tender and Drawing Gaps: What Is Usually Missing

Most disputes on stone work trace back to one of these gaps. If the tender does not answer them, raise them as queries before you bid or record them as assumptions in the offer.

Gap in the tender	Why it hurts	What to ask for or assume
Stone named only by trade name (“Kota”, “Tandur yellow”, “Jaisalmer”) with no thickness, calibration or finish	Thickness decides the bed and the adhesive quantity. Riven stone can vary by about ±5 mm (Nustone)	Thickness and tolerance, calibrated or gauged, finish and edge, sample reference
Fixing method not stated, or “as per standard practice”	Thin adhesive versus a 30–50 mm mortar bed changes material, weight and time several times over (CCFM)	Method stated per area, such as thin-bed, bonded bed or floating bed
Adhesive or grout “of approved make”	You price a basic adhesive and the architect approves a premium flexible (C2TE S1) grade, or epoxy	Named grade, or a price allowance with an adjustment clause
No substrate tolerance	The slab is out by 15–25 mm, and levelling becomes an unpaid scope	Thin and medium beds need about ±3 mm in 3 m; thick beds about ±6 mm (LAWA). Put screeding and levelling in as a separate item
No movement joint layout	Tenting and cracking later become your defect	Perimeter joints of at least 6 mm, field joints and substrate joints carried through (Laticrete)
Cladding “fixed with SS clamps” but no fixing design	The designer, anchor type, pull-out tests and wind load are left for you to carry	Fixing design responsibility, anchor specification and test frequency
Measurement rule unclear	Deductions for openings, skirting heights, and whether steps are measured flat or in running metres	Method of measurement stated, and special items listed separately
Special items bundled into the square-metre rate	Grooving, edge moulding, nosings, thresholds, drip grooves, kerfs, holes and mitres are all labour- or machine-intensive	Price each of these as a separate item (running metre or number)
Wastage “included”	Random or riven patterns can waste 10–15%, and book-matched marble more	State your assumed percentage and who owns the leftover stock
Marble or Kota floor with “polished finish” but no grinding item	In mortar-bed markets (India, the Middle East, southern Europe), the client expects on-site grinding: 2–3 grinds after 7 days of curing, then an oxalic, wax or diamond polish (Chhattisgarh PWD)	Clarify whether stone is factory-polished or polished at site; price grinding per m² with its extra days, water, power and slurry disposal
Protection, cleaning and sealing “included”	Weeks of protection while other trades work, sealer that cannot go on until after 21 days	Separate items, with the duration defined

 

Architectural Details That Often Don’t Close

• Floor build-up heights. Finished floor level minus slab level must equal stone plus bed plus membrane or screed. Where it doesn’t, especially at door thresholds, lift lobbies and toilet entrances, you will end up chipping the slab or thickening the screed.
• Level differences between wet and dry areas. If the drawings show no step, rebate or threshold, the waterproofing and the slope to the drain will not fit.
• Tiles or stone joining other finishes. The joint with carpet, wooden flooring or vinyl needs a trim or transition profile (LAWA). Nobody specifies it, and then everyone asks for it.
• Cladding cavity depth. Finished face minus structure face must work with the bracket range, insulation and tolerance. A structure out of plumb by 25–40 mm is common and pushes you into longer brackets or packing.
• Heights and weights of adhered cladding. Adhered veneer is generally limited to about 67 mm thick, 914 mm on its longest face, 0.46 m² and about 73 kg/m² (Masonal, CCFM). Large or heavy panels on external façades “stuck with adhesive” are a liability you should not accept without mechanical backup.
• Kerf and holing needs. A continuous kerf works best on stone of about 30 mm or more (AIA Florida). If the tender specifies 20 mm stone with a kerf system, raise it.
• Loads on upper floors and podiums. A thick mortar bed on a terrace or podium adds significant dead load. Confirm the structural engineer has allowed for it.

2. Stone Supply Risks

• Lead time and the risk of running out of a single block. Natural stone varies from block to block. If the quarry lot runs out mid-project, you get a visible shade change. Order the full quantity plus wastage up front from one lot, and specify blending on site (LAWA).
• Calibration assumptions. Rough (gauged) stone forces a full wet bed. Pricing thin-bed on uncalibrated stone is the most common costing mistake.
• Mesh-backed and moisture-sensitive stone. Green marble and mesh-backed tiles can fail on ordinary cement adhesive and need epoxy or rapid-hydrating adhesive (Laticrete TDS 120). The cost difference per square metre is significant.
• White and light stone. White marble and light limestone need white adhesive to avoid staining, which is another material upgrade.
• Breakage in transit. Agree the delivery form (crates or A-frames, never loose) and the rejection criteria at unloading. Otherwise the breakage becomes your cost.
• Factory work lead time for cladding. Kerfing, drilling to ±2 mm (Harrison Goldman), edge profiling and panel numbering all need approved shop drawings first. A late shop drawing approval means late stone, even when the stone itself is in stock.

3. Lead and Lift: The Hidden Cost Line

On stone work, lead and lift are often under-priced because the rate was built on a ground-floor, open-access assumption.

Factor	What to check	Impact
Unloading	Is there a crane or forklift, is there night-only entry, and how far is it from the gate to the stack?	Manual unloading of 40–60 kg slabs is slow and causes breakage
Stack area	Covered, level, off the ground, stone stored on edge	Rehandling if the stack area has to move for another trade
Horizontal lead	Distance from stack to hoist to work face; wheelbarrow or trolley access over finished floors	Labour-hours and damage to finished areas
Vertical lift	Hoist capacity and booking, whether panels fit inside the hoist car, tower crane time slots	Large slabs that won’t fit the hoist must be carried up stairs or craned at premium cost
Slab loading	Stacking pallets on a new slab or a finished floor	Needs structural approval; point loads crack fresh screed
Manual handling limits	Units over about 25 kg need two people or vacuum lifters	Gang size and productivity
Façade access	Scaffold, mobile elevating work platform, mast climber or cradle; who provides it, how long for, and whether scaffold ties clash with brackets	Scaffold hire often exceeds the fixing labour
Wastage from lifting	Chipped edges and cracked corners from rehandling	Extra stone, beyond the wastage allowance

 

Rule of thumb for pricing: build the lead and lift rate per floor band (ground to 4, 5 to 10, and so on), and state the assumed hoist availability in hours per day. If the builder’s hoist is shared, your productivity drops, and that should be a recoverable delay, not your loss.

4. Programme Risks: Waiting Times Are Not Optional

Clients push to compress stone work. The waiting time is what makes the stone stay stuck.

Stage	Typical minimum
New concrete before stone	About 28 days, as a common rule
Thin-bed stone to grouting	About 24 hours; 2–4 hours with rapid-set products (Laticrete, CCFM)
Grout to foot traffic	At least 24 hours at about 21 °C, longer in cold weather (Laticrete)
Paving to vehicles	About 7 days or more
Pervious screed to thin-bed	3–4 days (Sopro)
Scratch coat to veneer setting	24–48 hours (Masonal)
Sealing, indoor	About 21 days (LAWA)
Sealing, outdoor paving	3–6 months (APL/HTA)

 

In-situ grinding: add 7 days of curing plus 3–4 working days of grinding and polishing per area, and plan it before final painting. The slurry and water damage fresh paint and joinery.

Other programme traps:

• Mock-up approval. Allow 1–2 weeks, and do not mobilize the full gang before it is approved.
• Anchor pull-out tests on façades. These are a hold point, and a failed test means redesign.
• Fire barrier and insulation inspections. These are hold points before the panels close in the cavity.
• Adhesives are generally applied at about 4–32 °C (Laticrete). Summer afternoons on an exposed terrace and monsoon days on external paving both cut productive hours.
• Laying order with other trades. False ceilings, first coat of paint, services and door frames should come before the stone. When stone goes in first, you inherit the damage.

A note on sealing: outdoor sealing at 3–6 months usually falls after handover. Price it as a separate return visit or exclude it.

5. Protection and Damage by Others

Most rework on stone floors comes from other trades working over finished stone.

• Price protection as a separate item, in square meters per week of protection, not as “included”.
• Specify breathable protection boards. Plastic sheet laid directly on fresh work traps moisture and marks the stone.
• Get a written handover of protected areas, and photograph them. Damage after that point is chargeable to the trade that caused it.
• Ban on-floor mixing, cutting, welding and paint mixing, and require scaffold base boards. Make this part of the main contractor’s site rules, not just your request.
• On façades, cover completed lower panels while work continues above, and prohibit scaffold ties through stone.
• Set stone thresholds before door frames and casings, so the frames sit on finished stone (Stone Trades).

6. Quality Risks That Become Defect Claims

Defect	Usual root cause	Prevention
Hollow, drummy stones	Blob fixing, adhesive skinning over, no back-buttering	Full-spread notched trowel plus back-butter. Aim for about 95% coverage on thin stone (about 16 mm or less) and 80% on thicker stone, checked by lifting a stone at random (MIA via SPT)
Lippage (edges sticking up between stones)	Uncalibrated stone on thin bed; no levelling clips	Right bed for the stone; clips; check with a straight edge every bay
Cracks along a line	Substrate joint not carried through	Map slab joints and cracks before laying
Tenting or popping	No perimeter or field movement joints	Joints of at least 6 mm, kept clear of adhesive (Laticrete)
Staining or dark patches	Grey adhesive under light stone; resin from epoxy grout; sealant bleed	White adhesive; trial patch for grout; non-staining sealant (Laticrete TDS 191, Masonry Magazine)
White salt deposits on paving	Water wicking through the bed; bond bridge not used	Bond bridge primer, drainage falls, allow the stone to dry before sealing (APL/HTA, Paving expert)
Loose cladding panels	Wrong anchor, torque not recorded, overthick shims, kerf damage	Anchors with European technical approval (ETA), torque log, shims no thicker than the anchor diameter, a tested anchor sample (Harrison Goldman)
Corrosion at fixings	Stainless touching mild steel with no isolation	Neoprene, Tufnol or HDPE isolators (Harrison Goldman)
Acid etching	Site cleaners using acid on marble, limestone or Kota	Neutral cleaner only, written into your method statement

 

Keep records from day one: batch numbers, coverage checks, anchor torque sheets, test reports and photographs of protected areas. When a defect claim comes 8 months later, these records are your defence.

7. Commercial Checklist Before You Sign[ ] Stone thickness, calibration, finish and edge fixed in the contract, with a sample tagged

•  Fixing method per area in writing
•  Adhesive, grout and sealant grade named, or a price allowance with an adjustment clause
•  Substrate tolerance defined; levelling and screeding as a separate item
•  Movement joint layout issued, or the design responsibility clearly with the architect
•  Special items priced separately: grooving, moulding, thresholds, steps, kerf, holing
•  Wastage percentage stated, and ownership of leftover stone
•  Lead and lift by floor band; hoist and crane availability stated
•  Access for façades: who provides the scaffold or platform and for how long
•  Fixing design and anchor testing: who is responsible and who pays
•  Waiting times written into the programme; delays from compressed curing are not your risk
•  Finish route stated: factory-polished or ground and polished at site (passes, final polish)
•  Protection as a paid item; handover protocol for protected areas
•  Sealing timing and whether it is a return visit
•  Defect liability period and exclusions (damage by others, acid cleaning, lack of maintenance)
•  Mock-up and approval time allowed before mobilising

Stonework rewards contractors who price from the drawings, not from the tender rate. Most of the risks above cost little to close at tender stage, through a query, an assumption or a separate line item. They are very expensive to argue about after the stone is down.

The durations and tolerances quoted here are indicative industry values. The project specification and the manufacturer’s data sheets take priority where they differ.