Polished concrete flooring finish transforms ordinary concrete into a stunning, durable surface that rivals expensive alternatives. The process requires precise technique and proper equipment to achieve professional results.
We at Superfloor Australia see many contractors struggle with surface preparation and chemical application timing. This guide covers the essential steps to avoid costly mistakes and create floors that last decades.
Surface Preparation for Polished Concrete
Surface preparation determines 80% of your polished concrete project success. Concrete assessment starts with checking for structural integrity, measuring moisture levels with a calcium chloride test, and identifying cracks wider than 0.5mm that require repair. The Concrete and Cement Association of New Zealand reports that proper assessment prevents 90% of polishing failures. Test concrete strength with a rebound hammer – anything below 25 MPa needs densification before you begin the process.
Concrete Assessment and Repair Requirements
Check existing coatings, adhesive residue, and surface contamination first. Paint and sealers must be completely removed with 16-30 grit metal-bonded diamonds. Measure floor flatness with a 3-metre straightedge – variations that exceed 3mm need correction.
Fill cracks and holes with polymer-modified patching compound that matches the concrete’s expansion rate. Wait 24 hours minimum before you grind patched areas.
Grinding and Levelling Techniques
Start with 30-40 grit metal-bonded diamonds for initial work, and maintain consistent overlap patterns. Planetary grinders work best for residential spaces under 500 square metres, while walk-behind units handle larger commercial areas efficiently. Dry methods with dust extraction systems reduce cleanup time by 60% compared to wet alternatives. Progress through 80, 100, and 200 grit stages, and check surface uniformity at each step. Progressive grinding techniques ensure optimal surface preparation for the polishing process.
Cleaning and Moisture Testing
Concrete moisture content must stay below 75% RH before you seal the surface. Use plastic sheeting tests for 24 hours – any condensation indicates excessive moisture. Clean surfaces with industrial vacuums after each stage, and remove all dust particles that interfere with densifier penetration. Temperature should remain between 10-30°C during the entire process for optimal chemical reactions (this range allows proper curing and chemical bonding).
The foundation you create during surface preparation directly impacts how well your diamonds perform during the polishing stages.
Polishing Process and Equipment
Metal-bonded diamonds from 30 to 200 grit handle the heavy work, while resin-bonded diamonds from 400 to 3000 grit create the final polish. Start each grit stage with overlapping passes at 90-degree angles to eliminate scratches from previous stages. Transition to the next grit only when the surface shows uniform scratch patterns – rushed processes create permanent marks that show through the final finish. Planetary grinders with 7-10 inch heads work efficiently on residential projects, while 20-inch walk-behind units cover commercial spaces faster.
Diamond Grit Progression Stages
Begin with 30-40 grit metal-bonded diamonds to remove surface imperfections and level the concrete. Progress through 80, 100, and 200 grit stages systematically. Each stage removes scratches from the previous grit and prepares the surface for finer abrasives. Spend equal time on each grit level – typically 15-20 minutes per 100 square metres for residential applications. Check scratch patterns under bright lighting before you advance to prevent visible defects in the final finish.
Densifier Application and Chemical Timing
Apply liquid densifier after the 100-200 grit stage when concrete pores remain open for maximum penetration. Lithium silicate densifiers react within 30 minutes and continue to harden for 72 hours – never apply sealer during this period. Work the densifier into the surface with 400 grit resin diamonds while it remains wet for optimal chemical bonding. Temperature control remains critical – concrete above 35°C prevents proper densifier absorption and creates weak spots.
Resin Diamond Polishing Sequence
Progress through 800, 1500, and 3000 grit stages after densification completes. Resin-bonded diamonds create the smooth surface that reflects light effectively. Maintain consistent machine speed and overlap patterns throughout each stage. Water cooling becomes optional at higher grits, but dust extraction remains necessary for visibility and health safety.
Each grit stage should eliminate all scratches from the previous level before you proceed.
Final Polish and Sealer Application
High-speed burnishers at 1500-3000 RPM with non-diamond pads create the final mirror finish after 3000 grit diamonds. Apply penetrating sealer immediately after final polishing while concrete temperature stays below optimal levels for proper adhesion. Topical sealers require two thin coats with 45-minute intervals between applications – thick coats create cloudy finishes and adhesion problems. Test sealer compatibility on sample areas first, as some products react poorly with lithium densifiers and cause delamination within months.
Even perfect equipment and technique can fail without proper attention to common mistakes that plague many contractors.
Common Mistakes and How to Avoid Them
Surface preparation shortcuts destroy more polished concrete projects than any other factor. Contractors who skip moisture tests face sealer failure within 6-12 months, while inadequate crack repair creates visible lines that show through the final finish. Never advance to the next grit until scratch patterns show complete uniformity under bright lights.
Inadequate Surface Preparation Issues
Calcium chloride tests surface moisture, while relative humidity (RH) tests at 40% depth, measuring equilibrium moisture, and is considered the best indicator. Test concrete with calcium chloride strips for 24 hours before you apply any chemicals. Cracks wider than 0.5mm telegraph through every polish stage and create permanent defects in the final surface. Fill all holes and cracks with polymer-modified compounds that match the concrete’s expansion rate (thermal movement prevents cracking). Surface contamination from oils, adhesives, or previous coatings blocks densifier penetration and creates weak spots that fail under traffic loads.
Chemical Application Timing Errors
Densifier application at the wrong stage wastes material and weakens the surface permanently. Apply lithium silicate after 100-200 grit work when concrete pores remain fully open – earlier application gets ground away, while later application penetrates poorly through sealed surfaces. Temperature control prevents most chemical failures – concrete above 30°C during densifier application creates weak bonds that show up as cloudy patches within months. Sealer applied too soon over wet densifier causes delamination problems that require complete refinish work to fix properly.
Equipment Problems That Create Permanent Defects
Worn diamond segments leave deep gouges that show through every subsequent stage and the final polish. Replace metal-bonded diamonds when segments wear below 8mm height, and check resin diamonds for surface buildup that prevents proper cut action. Machine vibration from damaged drive systems creates chatter marks across the surface that become visible under certain light angles. Maintain consistent overlap patterns and machine speed – variations create wave patterns that reflect light unevenly and look unprofessional in the finished floor.
Final Thoughts
Professional polished concrete flooring finish demands systematic execution of each stage without shortcuts. Surface preparation determines 80% of project success, while proper chemical application prevents costly failures that plague rushed installations. Metal-bonded diamonds from 30-200 grit handle initial work, followed by resin-bonded progression through 3000 grit for mirror finishes.
Properly executed polished concrete floors last 20-30 years with minimal maintenance costs. Regular maintenance with pH-neutral products maintains surface integrity, while periodic resealing every 3-5 years protects against stains and wear patterns. The dust-resistant properties reduce maintenance frequency by 60% compared to untreated concrete surfaces (this makes them ideal for high-traffic areas).
DIY projects under 200 square metres can succeed with rental equipment and careful attention to grit progression. However, commercial installations require specialised planetary grinders and extensive experience with densifier chemistry. We at Superfloor Australia specialise in polished concrete flooring that transforms ordinary surfaces into durable, high-gloss finishes for residential, commercial, and industrial applications.