What professional slab preparation involves

1. Assessment

We look at the age and finish of the concrete, any existing coatings, cracks, joints, drainage falls and signs of moisture. We check whether the surface is weak or dusty and whether contamination such as oil has penetrated.

This decides the preparation method and whether any specialist products are needed.

2. Mechanical preparation

Manufacturer method statements typically call for mechanical preparation such as diamond grinding or shot blasting, rather than acid etching alone. The aim is to remove laitance (the weak top layer), old sealers and contaminants, and create a surface profile the primer can key into.

Sika guidance, for example, refers to profiles equivalent to ICRI CSP 3 for many coating systems, with rougher profiles for thicker systems. The exact requirement depends on the product data sheet for the system selected.

3. Dust extraction

Grinding produces fine concrete dust. We use connected dust extraction during grinding and vacuum thoroughly before priming, because dust left on the surface weakens the bond.

4. Repairs

Cracks, spalls, blow holes and damaged edges are opened up and filled with a compatible repair material. Guidance from manufacturers notes that blow holes and voids should be fully exposed during preparation so they can be filled rather than bridged.

• Hairline cracks may be filled and ground flush
• Moving joints are treated differently to static cracks
• Structural cracking needs separate advice

5. Moisture and conditions

Coatings are sensitive to moisture in the slab and to air and surface temperature during application. Manufacturers specify limits, including keeping the surface temperature above the dew point during curing. Where moisture is present, a moisture-tolerant primer or a different system may be appropriate.

What this means for you

Preparation is mostly invisible once the floor is finished, which is why it is easy to under-price. When comparing quotes, ask exactly how the slab will be prepared.