Is it better to grind or shotblast concrete before coating?
Depending on location, floor use, coating type and other variables, the best surface preparation method will vary. In some cases, floors are best ground AND shotblasted.
A few general statements to answer, what is the best equipment to prepare a concrete floor?
- Decorative coatings will benefit from removing high spots, and should be ground.
- Ground surfaces will have residual dust in the pores, and should be de-dusted if required by the material type.
- Protective coatings are typically thicker and will require shotblasting to meet the required CSP.
- Large floors will be prepared much quicker by shotblasting.
- Small and hard to reach areas will only be accessible with small hand grinders.
The picture above illustrates a floor that has been both ground, and shotblasted. You can see that even after multiple passes with a vacuum to remove dust, the shot-blaster is still able to remove loose particles.
What does grinding before coating do?
Grinding a concrete floor removes the surface and opens up the pores of the concrete. Depending on the selected tooling; grinding can polish, remove a surface layer, or cut down into aggregate. Airborne dust is collected, but the floor must be de-dusted to collect all loose particles from the substrate.
As a surface preparation method, grinding is the best method to remove highspots and texture. Grinding the concrete prior to coating will smooth the floor surface and reduce “puddled” areas of topcoat. Topcoats collects in low spots becoming thicker, and may be slippery or have a different aesthetic finish when compared to the rest of the floor.
Grinder size and weight will greatly impact if the floor is ground 100%. For example, three small grinders may only achieve a 80% ground surface compared to one larger grinder in the same amount of time. This is because the larger heavier grinder is flattening the floor much quicker while the smaller units are riding high spots.
Grinders will typically only be able to achieve a CSP 2. For most coatings, a minimum CSP 3 is required. While aggressive tooling sometimes can reach a CSP 3, it does so at the risk of digging into the concrete creating blemishes in the final coating.
How to fully prepare a floor with low spots?
Low spots can be adequately cleaned and profiled by using a shot-blaster.
A shot-blaster shoots steel shot at the concrete to remove the surface dirt and surface layers of concrete. Machine size, shot size, and travel speed will all determine the depth that is removed. Since the shot is hitting the surface perpendicular, it is able to create a more aggressive profile (CSP). Higher concrete surface profiles, mean there is a larger surface area present in the substate for material to bond to. The higher CSP therefore creates a much better material bond.
Shotblasting ground concrete surfaces also work to remove residual dust from the substrate. No amount of vacuuming a floor can replace the speed and effectiveness of a shot-blaster when removing dust from the pores of the concrete.