This guide provides step-by-step DIY procedures for common limestone repairs, clear criteria for when professional help is essential, cost comparisons, and procurement guidance for hiring qualified stone restorers. You’ll learn to assess damage severity, execute safe repairs, and prevent recurrence through proper maintenance.
Assessing Damage — Severity Triage (DIY vs Pro)
Level 1 — Cosmetic Hairline Scratches & Light Surface Abrasion (DIY Friendly)
Surface scratches that don’t catch your fingernail when you run it across the damage are typically DIY-repairable. Use angled lighting to reveal the full extent of scratching patterns. These marks usually result from furniture movement, grit accumulation, or improper cleaning tools.
Test scratch depth by gently running a fingernail perpendicular to the scratch. If the nail doesn’t catch, you’re dealing with surface-level damage that responds well to polishing compounds and progressive abrasive treatment.
Level 2 — Small Chips, Shallow Chips up to 3-5mm Depth, Edge Nicks (Possible DIY with Skill)
Measure chip dimensions using a ruler and probe depth carefully with a thin tool like a dental pick. Chips smaller than illustrative 20mm diameter and less than illustrative 5mm deep often respond to DIY epoxy filling and blending techniques.
Edge chips along tile borders or countertop edges are more challenging but manageable if the surrounding stone remains structurally sound. Look for radiating cracks extending from the chip—these indicate deeper structural issues requiring professional assessment.
Level 3 — Deep Chips, Structural Loss, Fractured Slabs, Wide Gouges (Call a Pro)
Professional restoration is essential when damage exceeds illustrative 25mm in any dimension, penetrates more than illustrative 6mm deep, or shows signs of underlying substrate movement. Fractured slabs, multiple chips in the same area, or damage affecting load-bearing elements always require expert evaluation.
Look for warning signs like hollow sounds when tapping near the damage, visible gaps under the stone, or cracks extending beyond the immediate repair area. These conditions indicate structural issues that DIY repairs cannot adequately address.
Quick Decision Checklist
- Fingernail catches in scratch → DIY polishing repair
- Chip smaller than coin, less than 5mm deep → DIY epoxy repair
- Edge damage with stable surrounding stone → Skilled DIY possible
- Multiple chips or spreading cracks → Call professional immediately
- Hollow sound when tapping → Professional structural assessment required
- Visible substrate or adhesive failure → Professional repair essential
Tools, Materials & Safety — What You Need for DIY Repairs
Essential Tools List
Polishing Equipment: Variable-speed angle grinder or rotary tool, diamond polishing pad set (illustrative 50-3000 grit progression), backup pad system, water spray bottle for wet polishing
Repair Tools: Fine metal files, putty knives (flexible and rigid), dental picks for detail work, mixing cups and stirring sticks, precision measuring tools, masking tape (low-residue)
Safety Equipment: Full-face respirator with P100 filters, safety goggles, nitrile gloves, hearing protection, non-slip work boots, dust collection system or shop vacuum
Materials List
Repair Compounds: Color-matched stone epoxy or polyester resin systems, pigment tints for color matching, micro-fiber reinforcement for deep repairs, denatured alcohol for cleanup
Surface Treatment: Progressive abrasive compounds, diamond polishing paste, breathable stone sealer for post-repair protection, lint-free cloths for final polishing
Safety & Environmental Notes
Ensure adequate ventilation when using resin systems—many contain volatile solvents requiring mechanical exhaust. Never use muriatic acid or other strong acids on limestone, as they cause permanent etching damage. Dispose of resin waste according to local hazardous material regulations.
Wear appropriate PPE consistently throughout the repair process. Stone dust from grinding operations poses respiratory hazards, while uncured resins can cause skin sensitization with repeated exposure.
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DIY Repair Procedures — Step-by-Step
Procedure A — Light Surface Scratch (Polish & Blend)
1. Clean and Test Area
Remove all dirt, oils, and cleaning residue from the scratch zone. Test the scratch depth using the fingernail technique to confirm it’s surface-level damage suitable for polishing repair.
2. Wet-Clean and Prepare
Clean the area with denatured alcohol to remove any remaining contaminants. Allow complete drying before beginning polishing operations. Mask surrounding areas to prevent accidental damage.
3. Progressive Polishing Sequence
Start with illustrative 220-grit diamond pad for initial scratch removal, progress through illustrative 400, 800, 1500, and 3000-grit stages. Use light pressure and keep the surface wet during polishing to prevent heat buildup.
4. Final Buffing and Sealing
Polish with diamond compound to restore original luster. Apply breathable sealer if the surrounding limestone is sealed, maintaining consistent protection levels across the repair area.
5. Quality Check
Inspect under various lighting conditions to ensure the scratch is invisible and the sheen matches surrounding stone. Test with light finger pressure to verify smooth surface transition.
Time & Cost: Illustrative 2-4 hours, illustrative $15-30 in materials for small scratch repair
Procedure B — Small Shallow Chip (Fill, Shape, Blend)
1. Area Preparation
Clean the chip thoroughly and mask surrounding limestone with illustrative 50mm border. Remove any loose fragments and clean with denatured alcohol. Allow complete drying before proceeding.
2. Color-Matched Epoxy Preparation
Mix stone epoxy according to manufacturer specifications, adding pigment tints to match the limestone color. Test color match on a hidden area before applying to the visible repair zone.
3. Application in Thin Layers
Apply epoxy in illustrative 2mm layers, allowing illustrative 30-45 minutes cure time between applications. Overfill the chip by illustrative 1mm to account for sanding and shaping operations.
4. Shaping and Progressive Sanding
After illustrative 24-hour full cure, file and sand the repair flush with surrounding stone. Progress through illustrative 220, 400, 800-grit sandpaper, then polish to match original sheen.
5. Final Sealing and Inspection
Apply appropriate sealer to match surrounding protection levels. Inspect for color match, texture consistency, and seamless integration with existing limestone surface.
Time & Cost: Illustrative 4-6 hours over 2 days, illustrative $25-45 in materials for typical small chip
Procedure C — Deep Gouge or Edge Repair (Temporary DIY Patch vs Pro Recommendation)
1. Structural Assessment
For gouges deeper than illustrative 6mm, assess whether the damage affects structural integrity. If the repair area exceeds illustrative 25% of the tile or slab area, professional restoration is recommended.
2. Reinforced Fill Method (Temporary Fix)
For acceptable deep repairs, use fiberglass mesh backing with structural epoxy. Build repair in illustrative 3mm layers, embedding mesh between layers for reinforcement. Allow illustrative 48-hour cure before shaping.
3. Professional Recommendation Triggers
Stop DIY repair if you encounter substrate damage, multiple fracture lines, or signs of underlying movement. These conditions require professional structural evaluation and specialized repair techniques.
Limitations: DIY deep repairs typically last illustrative 2-5 years versus illustrative 10+ years for professional restoration
Time & Cost: Illustrative 6-10 hours over 3 days, illustrative $40-75 materials, but consider professional repair for permanent solution
When to Call a Professional — Red Flags & What Pros Do Differently
Red Flags
Multiple chips across the same installation batch indicate potential substrate issues or installation problems requiring comprehensive evaluation. Hairline cracking spreading beyond the immediate damage zone suggests structural movement that DIY repairs cannot address.
Visible voids under slabs, hollow sounds when tapping near damage, or patches covering more than illustrative 30% of individual stone pieces require professional structural assessment. These conditions often indicate underlying issues that will cause DIY repairs to fail.
Professional Services
Professional stone restorers use CNC machinery for precise edge reproduction, thermal resin injection for deep structural repairs, and full re-honing to restore original surface characteristics. They have access to professional-grade color-matching systems and structural reinforcement techniques unavailable to DIY repairs.
Professionals can perform slab replacement, substrate remediation, and comprehensive installation repairs that address root causes rather than just surface symptoms.
Questions to Ask a Stone Restorer
“Please provide your business license, insurance certificates, and recent project portfolio with before/after photos of similar limestone repairs.”
“Can you provide an on-site color-matching sample and written warranty terms for this specific repair?”
“What is your standard test protocol for resin aging and adhesion, and can you provide technical data sheets for proposed repair materials?”
“Please provide three recent client references and detail your quality assurance procedures for final acceptance.”
Hiring & Specifying a Pro — Procurement Checklist & Acceptance Criteria
Simple Tender Checklist
Written Quote Requirements: Itemized breakdown showing materials, labor, equipment, and mobilization costs separately. Include material specifications, brand names, and technical data sheet references for all repair compounds.
Project Planning: Expected turnaround time, weather dependencies, dust control measures, and site protection protocols. Request sample mockup area for color and texture approval before proceeding with full repair.
Warranty Coverage: Minimum illustrative 2-year warranty on repair materials and workmanship, with clear terms for maintenance requirements and warranty exclusions.
On-Site Acceptance Criteria
Visual Match Standards: Repair should be invisible under normal indoor lighting and show no discernible color difference under daylight conditions. Texture and sheen must match surrounding limestone within illustrative 10% variation.
Performance Testing: Repair area should pass light adhesion testing, show no reaction to pH-neutral stone cleaners after illustrative 48-hour cure, and maintain structural integrity under normal use conditions.
Cost & Time Expectations — Illustrative Ranges
| Repair Type | Illustrative DIY Cost | Illustrative DIY Time | Illustrative Pro Cost | Illustrative Pro Time |
|---|---|---|---|---|
| Surface scratch polish | $15-30 | 2-4 hours | $75-150 | 1-2 hours |
| Small chip fill | $25-45 | 4-6 hours | $150-300 | 2-4 hours |
| Edge repair | $40-75 | 6-10 hours | $300-600 | 4-8 hours |
| Deep structural repair | Not recommended | N/A | $500-1,500 | 1-2 days |
| Full slab replacement | Not possible | N/A | $1,000-3,000 | 2-5 days |
Major Cost Drivers: Access difficulty, color matching complexity, structural reinforcement requirements, and finish level specifications significantly impact both professional and DIY costs.
Long-Term Care After Repair — Maintenance & Prevention
Immediate Post-Repair Care
Restrict foot traffic for illustrative 24-48 hours after repair completion to allow full cure. Use only pH-neutral stone cleaners for the first illustrative 30 days, avoiding aggressive cleaning that could compromise new repair bonds.
Monitor the repair area weekly for the first month, checking for any signs of separation, color changes, or performance issues that might indicate incomplete curing or compatibility problems.
Preventative Tips
Install furniture pads and protective mats in high-traffic areas to prevent future scratching and chipping. Maintain consistent sealer protection across the entire limestone surface to ensure uniform performance and appearance.
Never use vinegar, lemon juice, or acid-based cleaners on limestone, as these cause permanent etching damage that requires professional restoration. Address spills immediately to prevent staining that complicates future repairs.
Recommended Monitoring Schedule
Inspect repaired areas quarterly during the first year, then annually thereafter. Document any changes in appearance, performance, or structural integrity. Schedule preventative maintenance before minor issues become major repair needs.
Illustrative monitoring intervals: Weekly for first month, monthly for first quarter, quarterly for first year, annually thereafter
Common Pitfalls & Troubleshooting — What Can Go Wrong With DIY Repairs
Poor Color Match: Test repair compounds on hidden areas first. Build color gradually with multiple thin coats rather than attempting single-application matching.
Visible Epoxy Lines: Use proper masking techniques and sand repairs flush with surrounding stone. Over-polishing can create depression lines—stop when achieving proper surface level.
Sand-Through to Filler: Start with finer grits when shaping repairs. If sand-through occurs, clean area and apply additional filler material before continuing.
Sealer Incompatibility: Test sealer compatibility on repair samples before applying to visible areas. Some repair resins reject certain sealer formulations.
Thermal Discoloration: Avoid overheating during polishing operations. Use adequate cooling and light pressure to prevent resin thermal degradation.
Quick Reference — DIY vs Pro Decision Flow (Textual)
Step 1: Measure damage dimensions and depth using ruler and probe tool
Step 2: Perform fingernail test—if nail catches, assess whether chip is structural
Step 3: Check for multiple damages, cracks, or substrate issues
Step 4: Evaluate your skill level and available time for multi-day repair process
Step 5: Consider long-term performance needs and warranty requirements
Step 6: If damage exceeds illustrative 25mm diameter or illustrative 6mm depth, consult professional
Step 7: For edge damage or load-bearing areas, lean toward professional assessment
Step 8: When in doubt, get professional opinion before attempting DIY repair.
DIY Repair Procedures
Procedure A: Surface Scratch Repair
- Clean area thoroughly with denatured alcohol
- Test scratch depth with fingernail technique
- Mask surrounding area with illustrative 50mm border
- Begin with illustrative 220-grit diamond pad, progress through 400, 800, 1500, 3000-grit
- Keep surface wet during polishing, use light pressure
- Apply diamond polishing compound for final luster
- Seal if surrounding limestone is sealed
- Quality check under multiple lighting conditions
Materials: Diamond pad set, polishing compound, denatured alcohol, masking tape, sealer
Safety: Respirator, goggles, gloves, hearing protection
Time: Illustrative 2-4 hours
Cost: Illustrative $15-30
Procedure B: Small Chip Fill Repair
- Clean chip and mask illustrative 50mm border around damage
- Remove loose fragments, clean with denatured alcohol
- Mix color-matched epoxy according to manufacturer specifications
- Apply in illustrative 2mm layers with illustrative 30-45 minute cure between coats
- Overfill by illustrative 1mm for sanding allowance
- Allow illustrative 24-hour cure before shaping
- File and sand flush, progress through 220, 400, 800-grit
- Polish to match surrounding sheen, apply sealer
Materials: Stone epoxy, pigment tints, sandpaper progression, files, sealer
Safety: Respirator, gloves, goggles, adequate ventilation
Time: Illustrative 4-6 hours over 2 days
Cost: Illustrative $25-45
Procedure C: Deep Gouge Repair (Temporary)
- Assess structural integrity—stop if damage exceeds illustrative 25% of stone area
- Clean thoroughly and prepare fiberglass mesh reinforcement
- Apply structural epoxy in illustrative 3mm layers, embedding mesh between layers
- Build repair illustrative 2mm above surface level
- Allow illustrative 48-hour full cure before shaping
- Shape with files and progressive sanding to match surrounding surface
- Polish and seal to match existing protection
Materials: Structural epoxy, fiberglass mesh, files, sandpaper, sealer
Safety: Full PPE, excellent ventilation, proper resin disposal
Time: Illustrative 6-10 hours over 3 days
Cost: Illustrative $40-75
Limitation: Temporary fix lasting illustrative 2-5 years
Tools & Materials Checklist
Essential Tools:
- Variable-speed angle grinder or rotary tool
- Diamond polishing pad set (50-3000 grit)
- Fine metal files and putty knives
- Mixing cups and stirring sticks
- Precision measuring tools
- Low-residue masking tape
Materials:
- Color-matched stone epoxy/polyester resin
- Pigment tints for color matching
- Fiberglass mesh for structural repairs
- Progressive abrasive compounds
- Diamond polishing paste
- Breathable stone sealer
- Denatured alcohol for cleanup
Safety Equipment:
- P100 respirator with full face protection
- Safety goggles and nitrile gloves
- Hearing protection
- Dust collection system
- Non-slip work boots
Decision Checklist (DIY vs Pro)
DIY Appropriate When:
- Damage smaller than illustrative 20mm diameter
- Depth less than illustrative 5mm
- No structural cracking visible
- Single isolated damage point
- Adequate skill and tool access
- Non-critical aesthetic area
Professional Required When:
- Multiple chips or spreading cracks
- Damage exceeds illustrative 25mm in any dimension
- Depth greater than illustrative 6mm
- Structural or substrate issues present
- Load-bearing or high-visibility areas
- Warranty requirements mandate professional work
Procurement/Hiring Checklist and Acceptance Criteria
Pre-Contract Requirements:
- Business license and insurance verification
- Portfolio of similar limestone restoration projects
- Written warranty terms (minimum illustrative 2 years)
- Detailed quote with material specifications
- Timeline and weather dependency planning
- Sample mockup for approval
Quality Acceptance Standards:
- Invisible repair under normal lighting conditions
- Color match within illustrative 10% variation
- Texture and sheen consistency with existing stone
- No reaction to pH-neutral cleaners after cure
- Structural integrity under normal use
- Complete cleanup and site restoration
Illustrative Cost & Time Table
| Repair Category | DIY Cost Range | DIY Time | Professional Cost | Pro Time |
|---|---|---|---|---|
| Surface scratch | Illustrative $15-30 | 2-4 hrs | Illustrative $75-150 | 1-2 hrs |
| Small chip | Illustrative $25-45 | 4-6 hrs | Illustrative $150-300 | 2-4 hrs |
| Edge damage | Illustrative $40-75 | 6-10 hrs | Illustrative $300-600 | 4-8 hrs |
| Deep repair | Not recommended | N/A | Illustrative $500-1,500 | 1-2 days |
| Slab replacement | Impossible | N/A | Illustrative $1,000-3,000 | 2-5 days |
Cost Variables: Access difficulty, color complexity, structural requirements, finish specifications
Maintenance & Prevention Schedule
Weekly: Visual inspection of repair areas, immediate spill cleanup, gentle cleaning with pH-neutral products
Monthly: Detailed inspection for any changes in repair appearance or performance, furniture pad check and replacement
Quarterly (First Year): Comprehensive repair assessment, photo documentation of any changes, sealer condition check
Annually: Professional inspection if repairs show any deterioration, preventative maintenance planning, sealer renewal assessment
Prevention Measures:
- Install furniture pads and protective mats
- Maintain consistent sealer protection
- Use only pH-neutral stone cleaners
- Address spills within illustrative 15 minutes
- Avoid dragging heavy objects across limestone.
Classic Limestone Tiles for Any Project
Case Study 1: Milwaukee, WI — Brewery Conversion Taproom (limestone paver installations)
Project overview
A former brewery in Milwaukee was converted into a taproom and tasting hall. The owners wanted a neutral, durable floor that would handle heavy foot traffic and occasional spills while reinforcing the industrial character.
Paver selection rationale
Large-format honed white limestone (24″×48″) with a low-sheen finish was selected to minimize grout lines and create a seamless visual field. The stone’s density and low porosity made it suitable for a high-traffic commercial limestone paving application.
Installation challenges
The old concrete floor had oil contamination from decades of brewery use. Crews removed contaminated concrete, installed a new cementitious leveling screed, and applied a decoupling membrane (a thin layer that isolates the tile from substrate movement) to prevent future cracking.
Outcomes & key metrics
Budget adherence: 3% under the $52,000 allocation.
Completion time: 5 weeks, including remediation.
Performance results: Over 18 months, staff reported a 40% reduction in floor-related maintenance calls versus the previous terrazzo surface.
How Citadel Stone helped
Conducted on-site contamination testing and recommended remediation methods.
Supplied mockup panels to confirm finish under taproom lighting.
Provided installer referrals experienced with decoupling membranes and high-traffic commercial paving.
Case Study 2: Birmingham, AL — University Lecture Hall Renovation (limestone paver case studies for education)
Project overview
A mid-sized university renovated a large lecture hall lobby to improve acoustics and create a durable arrival zone for students.
Paver selection rationale
Matte honed white limestone with acoustic underlayment beneath the floor was chosen to reduce reverberation while giving the lobby a contemporary, academic look. The stone’s smooth surface also simplifies daily cleaning.
Installation challenges
The project required alignment of movement joints with the building’s structural joints to avoid stress cracks. Installers also phased work to avoid disrupting class schedules.
Outcomes & key metrics
Budget adherence: On budget at $36,000.
Completion time: 4 weeks, phased around the academic calendar.
Performance results: Post-install testing showed a 14% reduction in reverberation time and custodial teams reported 20% faster floor maintenance cycles.
How Citadel Stone helped
Produced joint-layout drawings that aligned tile movement joints with structural elements.
Recommended an acoustic underlayment compatible with limestone and provided performance data.
Offered a post-install maintenance schedule for university facilities staff.
Case Study 3: Memphis, TN — Riverfront Restaurant Terrace (residential limestone paver approach for hospitality)
Project overview
A riverfront restaurant in Memphis updated its outdoor terrace to improve guest comfort and safety while maintaining a bright, coastal aesthetic.
Paver selection rationale
Textured white limestone pavers (2 cm exterior grade) were selected for slip resistance and low heat absorption. The light color keeps the terrace comfortable for bare feet and outdoor seating.
Installation challenges
Proximity to the Mississippi requires salt-air resistance and robust drainage. Contractors installed a layered stone base with a secondary drainage plane and used marine-grade sealants.
Outcomes & key metrics
Budget adherence: 2% over the $28,000 forecast due to additional drainage work.
Completion time: 3.5 weeks, including drainage implementation.
Performance results: First season reported zero slip incidents and a 12% increase in terrace bookings.
How Citadel Stone helped
Specified a salt-tested sealer and produced a terrace drainage detail to prevent water pooling.
Supplied production lots matched for color consistency and coordinated quick delivery windows for seasonal opening.
Case Study 4: Albany, NY — State Office Building Lobby Refresh (limestone paver installations for public sector)
Project overview
A state office building in Albany refreshed its lobby to modernize the public entrance and reduce long-term maintenance costs.
Paver selection rationale
Dense, semi-polished white limestone slabs were chosen for their stain resistance and ease of cleaning in a public setting. Large slabs minimize grout lines and provide a dignified, continuous surface appropriate for civic spaces.
Installation challenges
Integration with existing radiant heating runs demanded exact thickness tolerances and verified thermal compatibility. The team also coordinated phased access to maintain public entry.
Outcomes & key metrics
Budget adherence: On budget at $68,000.
Completion time: 6 weeks, phased to maintain public services.
Performance results: Maintenance logs showed a 28% reduction in cleaning time and no grout deterioration after 12 months.
How Citadel Stone helped
Provided a thermal-compatibility spec for flooring over radiant heat (ensuring the stone and adhesive tolerate temperature cycles).
Coordinated phased deliveries and issued an installation QA checklist for the contractor and building staff.
Case Study 5: Oklahoma City, OK — Contemporary Suburban Home (residential limestone paver)
Project overview
A newly built suburban home in Oklahoma City selected white limestone flooring throughout the main floor to create a neutral backdrop for furnishings and artwork.
Paver selection rationale
Honed white limestone, 12″×24″, was selected for durability, moderate sheen, and low maintenance—ideal for family living. The honed surface balances slip resistance and an elegant matte appearance.
Installation challenges
The builder needed rapid turnaround to meet closing deadlines. Crews implemented a fast-track schedule using rapid-set adhesives compatible with limestone to speed cure times without sacrificing bond strength.
Outcomes & key metrics
Budget adherence: 1% under a $13,500 budget.
Completion time: 2.5 weeks, fast-tracked for closing.
Performance results: Homeowner survey at 6 months indicated very high satisfaction with wear resistance and cleaning ease.
How Citadel Stone helped
Recommended rapid-set, limestone-compatible adhesives and provided cure-time protocols.
Delivered pre-blended sample boxes for owner sign-off to avoid last-minute SKU changes that delay close.
Case Study 6: Knoxville, TN — Mountain View Retreat Entry & Sunroom (limestone paver installations in mixed climate)
Project overview
A weekend mountain retreat near Knoxville needed flooring that withstands humidity, occasional freeze, and heavy footwear while harmonizing with wood interiors.
Paver selection rationale
Tumbled white limestone paving tiles with slight texture was chosen for the sunroom and entry to hide wear marks and provide traction. The stone’s moderate porosity was addressed with a penetrating sealer to guard against stains.
Installation challenges
Seasonal humidity swings needed a grout and sealer system that tolerates expansion and contraction. Installers used wider movement joints at exterior transitions and a flexible epoxy grout in key locations.
Outcomes & key metrics
Budget adherence: 2% under the $11,000 estimate.
Completion time: 3 weeks, including sealer cure.
Performance results: After one winter and summer cycle, the floor showed no grout cracking and owners reported easy clean-up of tracked-in mud.
How Citadel Stone helped
Advised on a flexible grout and penetrating sealer system tailored to seasonal movement.
Provided installer training on proper joint spacing and on the recommended sealer re-coat schedule to maximize long-term performance.
Troubleshooting List (Common Pitfalls & Fixes)
Poor Color Match
Cause: Insufficient color testing, wrong pigment selection
Fix: Remove repair, re-test color on hidden area, rebuild with proper pigments
Visible Repair Lines
Cause: Inadequate masking, poor sanding technique
Fix: Re-sand with progressive grits, blend edges gradually
Epoxy Separation
Cause: Contaminated surface, incompatible materials
Fix: Remove failed repair, clean with denatured alcohol, verify material compatibility
Over-Polishing Depression
Cause: Too aggressive polishing, excessive pressure
Fix: Apply additional filler, re-sand with lighter technique
Sealer Rejection
Cause: Resin incompatibility with sealer chemistry
Fix: Test sealer on repair sample, use compatible sealer system
Thermal Discoloration
Cause: Overheating during polishing operations
Fix: Use water cooling, reduce speed and pressure, allow cooling between passes
