Mechanically polished Concrete/MPC Guidelines/Slab Quality
Important Slab Note:
A common misconception is that any standard slab can achieve a premium mirror reflection. Inexperienced operators promise high-end finishes without realizing concrete must be poured to strict trade specifications. Premium polishing relies entirely on uniform stone distribution and high cement paste density. Local mix problems—like poor aggregate grading, the use of soft limestone cement, unwashed sands, or even crusher dust can cause the surface chemistry to fail.
New Slabs – Mix Design & Pre-Pour Specs
- Cement Type Type GP (General Purpose) cement only. To achieve a high-quality polished finish, cement replacement in concrete is typically limited to 20% for Fly Ash (Type GB), 30% for Slag (GGBFS), and 10%–12% for Limestone (Type GL). Exceeding these amounts can lead to issues like soft, chalky paste and poor visual results.
- Compressive Strength: Minimum 32 MPa structural mix (40 MPa highly recommended for premium zero-stone or nil-exposure finishes).
- Zero Crusher Dust: The mix must use clean, washed sharp sands. Crusher dust destroys the cement paste density, absorbs excessive water, and leaves a dead, dusty, micro-pitted surface that cannot take a crisp, high-gloss mechanical polish.
- Water Control: Diluted cement paste causes aggregate segregation (sinking the stone to the bottom mesh) and leaves a weak, dusty “cream” surface layer that won’t hold a mechanical edge.
- Chemical Controls: Controlled water-reducers only. Strictly no heavy overdosing of superplasticisers or fluidisers to force an “easy” self-levelling pour. Overdosing separates the mix and leaves a gummy, rubbery surface.
- Curing & Processing Windows: Slabs using standard Type GP cement must cure for 28 days minimum before grinding. If the plant supplies a different blend, the processing timeline may be extended to 45+ days to account for slower early strength.
Local DIY Supplies Warning: Do not apply any curing products, chemical compounds, or retail sealers without asking first. The truth is, the local DIY supply shops do not know what they are selling when it comes to mechanical polishing preparation. Off-the-shelf retail products can create permanent barriers that completely block the liquid densifiers and chemical hardeners we must inject during our polishing stages—effectively ruining our entire refinement process.