Quick Contractor Checklist — At a Glance (Printable)
Pre-Installation Subfloor Preparation Checklist
- Site Survey — Document substrate type, existing conditions, penetrations
- Substrate Identification — Confirm slab composition, age, existing coatings
- Moisture Testing — Perform RH and/or CaCl tests, document results
- Flatness Assessment — Check with straightedge, laser level, measure deviations
- Level Verification — Confirm proper slopes for drainage areas
- Deflection Check — Test wood substrates for L/360 compliance
- Crack Assessment — Map existing cracks, evaluate movement potential
- Remediation Work — Grind high spots, fill low areas, install underlayments
- Joint Layout — Plan movement joints over existing control joints
- Priming Application — Apply appropriate primers per manufacturer specs
- Adhesive Selection — Confirm ANSI classification matches substrate/stone
- Mockup Installation — Complete test panel for approval
- Protective Staging — Establish material protection and work zone barriers
- Final Acceptance — Document all tests, obtain signed approvals
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Substrate Types & What Each Requires
Concrete slabs (new & existing)
New concrete requires minimum illustrative 28-day cure before moisture testing. Check for surface contamination from curing compounds or sealers that prevent adhesive bonding. Remove all bond-breaking materials through grinding, shot-blasting, or chemical stripping.
Install saw-cut control joints at illustrative 4.5-6.0m spacing maximum to control shrinkage cracking. Existing slabs require crack mapping and evaluation for continued movement. Apply crack isolation membranes over active cracks or use full uncoupling membrane systems.
Cement backer boards & cementitious screeds
Acceptable for contractor limestone installation when properly fastened and supported. Use corrosion-resistant fasteners at illustrative 200mm centers along edges, 300mm centers in field areas. Verify flatness tolerances and apply appropriate primers before adhesive application.
Consider decoupling membranes over cement boards in areas subject to thermal cycling or minor structural movement to prevent stress transfer to limestone.
Plywood / wood framed subfloors
Minimum illustrative 25mm exterior-grade plywood over properly spaced joists. Verify deflection limits meet illustrative L/360 under full load. Install 6-12mm cement backer board with appropriate fasteners and uncoupling membrane systems to isolate limestone from wood movement.
Gap plywood sheets illustrative 3mm at edges and seal with flexible caulk. Ensure adequate ventilation beneath subfloor to prevent moisture accumulation.
Existing ceramic/terrazzo/stone
Remove loose or hollow-sounding tiles completely. Sound existing installations can receive overlay treatment with proper surface preparation and bonding agents. Grind glazed surfaces to provide mechanical bond, clean thoroughly, and apply appropriate primers.
Test bond strength with pull-test samples before proceeding with full installation.
Lightweight decks / elevated substrates
Use pedestal systems or structural floating beds for proper drainage and access. Ensure structural adequacy for limestone dead loads plus live loads. Install vapor barriers and insulation per building code requirements.
Coordinate with structural engineer for loading calculations and deflection limits.
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Moisture Testing — What To Do, How To Read Results
Relative Humidity (in-situ probe) Protocol
Install probes at illustrative 40% of slab depth for slabs up to 100mm thick, 20% depth for thicker slabs. Use illustrative one probe per 90m² of area, minimum three probes per job. Drill holes with clean masonry bits, vacuum debris, and seal probes with manufacturer-supplied caps.
Allow illustrative 72-hour equilibration before reading. Record ambient temperature and RH during testing. Document probe locations on floor plan with numbered identification.
Verify current ASTM F2170 standard procedures before testing.
Calcium Chloride (moisture vapor emission) Protocol
Place test dishes on clean, prepared substrate per manufacturer instructions. Seal test area with plastic dome, ensuring complete air seal. Maintain illustrative 24°C ± 3°C ambient temperature during illustrative 60-72 hour test period.
Use illustrative one test per 90m² area, minimum three tests per project. Weigh dishes before and after testing using calibrated scale accurate to illustrative 0.01g.
Verify current ASTM F1869 procedures and calculation methods.
Moisture Test Results Table
| Test Method | Sampling Density | Illustrative Acceptable Range | Action Required |
|---|---|---|---|
| RH (in-situ) | 1 per 90m² | ≤75% RH for most adhesives | >75%: vapor barrier/mitigation |
| Calcium Chloride | 1 per 90m² | ≤1.4 kg/m²/24hr | >1.4: extended drying/barrier |
| Combined Testing | Both methods | Must pass both limits | Investigate discrepancies |
All thresholds are illustrative — verify with adhesive manufacturer specifications
Troubleshooting Moisture Results
Discrepant RH versus CaCl results indicate potential surface contamination or non-uniform moisture distribution. Investigate readings near plumbing penetrations or exterior walls. Temporary mitigation includes dehumidification, increased ventilation, and extended drying time before retesting.
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Flatness, Level & Deflection — Numeric Targets & Tools
Flatness Requirements
Limestone subfloor checklist requires flatness tolerances of illustrative 3mm over 3m for large-format limestone, 6mm over 3m for smaller formats. Use 3m straightedge with feeler gauges, laser levels, or electronic measuring devices.
Document measurements at regular grid intervals and photograph any areas requiring remediation.
Level Requirements
Maintain proper slopes for drainage: illustrative minimum 1:100 away from drains, 1:50 toward floor drains in wet areas. Use water-level or digital inclinometer for accurate slope verification.
Deflection Testing
Wood-framed substrates must limit deflection to illustrative L/360 under design loads. Load test with sandbags or equivalent distributed weight. Measure deflection with dial gauges or laser measurement tools.
Remediation Options
High spots: Diamond grinding with dust collection systems Low spots: Self-leveling compounds or cement-based patch materials Major irregularities: Overlay screeds or complete slab replacement Excessive deflection: Additional structural support or joist stiffening
Crack Isolation, Movement Joints & Control Joints — Placement & Products
Movement joints must align with existing structural joints and occur at illustrative maximum 8m spacing in limestone installations. Install crack isolation membranes over all existing cracks wider than illustrative 0.5mm.
Use polyethylene or rubber-based crack isolation membranes with appropriate adhesives. Install joint profiles with proper depth-to-width ratios: illustrative 6-12mm width, 6mm minimum depth.
Underlayments, Uncoupling Membranes & Vapor Controls
Decision Matrix by Substrate Type
Concrete Slab (dry): Primer + appropriate adhesive Concrete Slab (marginal moisture): Vapor retarder + adhesive system Concrete Slab (high moisture): Full vapor barrier + floating system Wood Substrate: Cement board + uncoupling membrane Existing Tile: Bonding primer + crack isolation membrane Problematic Substrate: Full uncoupling system with vapor control
Product Categories
Cementitious underlayments provide leveling and increased mass. Uncoupling membranes (Ditra-type) allow independent movement. Crack isolation membranes bridge static cracks. Vapor barriers prevent moisture migration.
Select based on moisture test results, substrate movement potential, and limestone format size.
Adhesives, Mortars & Bedding Choices for Limestone
Recommended Adhesive Classifications
Use ANSI A118.4 or A118.15 modified thinset adhesives for most limestone substrate prep applications. Rapid-set formulations (A118.9) for fast-track schedules. Epoxy adhesives (A118.3) for problematic substrates or high-stress applications.
Verify current ANSI A118 classification numbers before specifying.
Coverage Calculation Example
600mm × 600mm limestone tile with 10mm × 10mm notch trowel:
- Theoretical coverage: 2.8 m² per 25kg bag (manufacturer data)
- Actual coverage adjustment: 2.8 × 0.85 = 2.38 m² (15% reduction for real conditions)
- Project area: 100 m²
- Bags required: 100 ÷ 2.38 = 42.0 bags
- Add waste factor: 42.0 × 1.10 = 46.2 bags
- Order 47 bags minimum
Working Properties
Open time: illustrative 15-30 minutes depending on conditions Pot life: illustrative 90-120 minutes for powder-based systems Working temperature: illustrative 10-32°C for normal cure Full cure: illustrative 24-48 hours before grouting
All values are illustrative — verify with specific product data sheets
Mockup Panel & Dry Run — What to Require Before Bulk Install
Mockup Requirements
Minimum illustrative 1.2m × 1.2m panel including edge transitions, typical joint widths, and grout color samples. Install over identical substrate preparation as production areas.
Apply sealer test patches to evaluate appearance and performance. Document installation techniques, adhesive coverage, and timing for production reference.
Mockup Acceptance Criteria
- Limestone placement matches approved layout drawings
- Joint widths consistent within illustrative ±1mm tolerance
- No lippage exceeding illustrative 1mm between adjacent tiles
- Grout color matches approved sample
- Sealer application provides uniform appearance
- Adhesive coverage exceeds illustrative 85% contact area
- No voids or air bubbles in adhesive bed
- Clean installation with no staining or residue
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QA Punchlist — Final Acceptance Checks
Final Subfloor Acceptance Checklist
- Moisture Reports — RH and CaCl test results within specifications, attached to file
- Flatness Verification — Straightedge check confirms tolerances met, documented
- Joint Placement — Movement joints align with structural joints, proper spacing
- Surface Preparation — All bond-breaking materials removed, primers applied
- Underlayment Installation — Membranes properly overlapped, seams sealed
- Adhesive Selection — ANSI classification matches substrate and limestone requirements
- Mockup Approval — Test panel accepted in writing, techniques documented
- Material Staging — Limestone and adhesives protected from contamination
- Environmental Conditions — Temperature and humidity within installation range
- Documentation Package — All test reports, approvals, and photos compiled
- Contractor Signature — Installation team leader accepts substrate conditions
- Owner Representative Signature — Authorized approval to proceed with limestone installation
Date: _________ Project: _________ Substrate Area: _________ m²
Common Failure Modes & How to Prevent Them
Moisture Vapor Blistering
- Cause: Excessive slab moisture, inadequate vapor control
- Prevention: Proper moisture testing, vapor barriers when required
Debonding at Cold Joints
- Cause: Construction joints not properly treated
- Prevention: Crack isolation membranes over all joints
Efflorescence After Sealing
- Cause: Residual moisture trapped in substrate
- Prevention: Complete drying, breathable sealers only
Lippage from Uneven Substrate
- Cause: Inadequate flatness preparation
- Prevention: Proper leveling, appropriate adhesive thickness
Staining from Iron/Contaminants
- Cause: Substrate contamination, metallic aggregate exposure
- Prevention: Complete surface cleaning, stain-blocking primers.
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Tools, Materials & Safety Checklist (Contractor Worksite List)
Testing Equipment
- RH probe rental kit with calibrated sensors
- Calcium chloride test kits (multiple sets)
- Digital moisture meters for reference checks
- 3m straightedge with feeler gauges
- Laser level or water level for slope verification
- Dial gauges for deflection measurement
Installation Tools 7. Diamond grinders with dust collection 8. Self-mixing drill with paddle attachments 9. Notched trowels (multiple sizes) 10. Membrane application rollers 11. Joint cutting tools and profiles
Safety Equipment 12. Respirators and dust masks 13. Safety glasses and hearing protection 14. Non-slip footwear and knee protection 15. First aid supplies and emergency contacts
Consumables 16. Primers and bonding agents 17. Membrane rolls and adhesive tapes 18. Patch compounds and leveling materials 19. Cleaning solvents and preparation chemicals.
Illustrative Tables & Quick References
Moisture Testing Summary Table
| Method | Test Duration | Illustrative Limit | Mitigation Required |
|---|---|---|---|
| RH In-Situ | 72+ hours | ≤75% RH | >75%: vapor barrier |
| Calcium Chloride | 60-72 hours | ≤1.4 kg/m²/24hr | >1.4: extended drying |
| Combined Results | Both tests | Pass both limits | Investigate discrepancies |
Flatness & Deflection Quick Reference
| Measurement Method | Illustrative Tolerance | Typical Remediation |
|---|---|---|
| 3m Straightedge | 3mm max deviation | Grinding, self-leveling |
| Laser Level | 1:100 slope minimum | Re-screeding |
| Deflection Test | L/360 maximum | Structural reinforcement |
All values are illustrative unless project-verified
Sample Calculations (Coverage & Waste)
Calculation 1: Thinset Coverage for 600×600mm Limestone
Given: 10mm × 10mm square-notch trowel, 25kg adhesive bag Manufacturer Coverage: 2.8 m² per bag (theoretical)
- Apply coverage reduction factor: 2.8 × 0.85 = 2.38 m² (actual coverage)
- Project area calculation: 50m × 20m = 100 m²
- Bags required: 100 ÷ 2.38 = 42.02 bags
- Round up to whole bags: 43 bags minimum
- Add waste factor: 43 × 1.10 = 47.3 bags
- Final order: 48 bags
Calculation 2: Limestone Order Quantity with Cuts/Waste
Given: 100 m² project area, 600×600mm tiles (0.36 m² each) Base requirement: 100 ÷ 0.36 = 278 tiles
- Add cutting waste: 278 × 1.08 = 300 tiles (8% waste factor)
- Add breakage allowance: 300 × 1.05 = 315 tiles (5% breakage)
- Round up to full boxes: 315 ÷ 20 = 15.75 = 16 boxes
- Final order: 320 tiles (16 boxes × 20 tiles/box)
- Total coverage: 320 × 0.36 = 115.2 m² (15.2% total overage)
Waste percentages are illustrative — adjust for project complexity.
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FAQs — Short Practical Answers
Q: Which moisture test should I trust most? A: Use both RH and calcium chloride tests for complete assessment. RH measures internal slab moisture, while CaCl measures surface emission. Discrepancies indicate surface contamination or non-uniform conditions.
Q: How long must concrete cure before installing limestone? A: Minimum illustrative 28 days for standard concrete. High-early-strength mixes may cure faster, but always verify with moisture testing before proceeding.
Q: When is an uncoupling membrane mandatory? A: Required over wood substrates, existing tile, problematic slabs with active cracks, and areas subject to thermal cycling or structural movement.
Q: What deflection limit applies for stone over wood? A: Illustrative L/360 maximum deflection under full design loads. Verify with structural engineer for specific loading conditions and span calculations.
Q: Can I use cement board over a damp slab? A: No. Cement board is not a vapor barrier. High moisture levels require proper vapor control systems before any tile backer installation.
Q: How much extra limestone should I order for cuts/waste? A: Illustrative 8-12% for cuts plus 5% for breakage, total 15-20% overage depending on pattern complexity and installer experience.
Next Steps & Resources
Proper subfloor preparation for limestone ensures successful installations and long-term performance. Follow this systematic checklist approach to prevent common failures and protect project warranties.
For detailed limestone installation techniques and advanced troubleshooting guidance, see our Limestone Installation Guide. Technical questions about specific substrate conditions can be addressed through our Request Technical Support & Mockups service.
Remember: successful limestone installations start with properly prepared substrates. Never compromise on preparation quality to meet schedule pressures.
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