How do you get a Class A Burnished concrete finish?
Burnished concrete is the polished concrete finish where there is no aggregate exposed. This is a finish that is becoming very popular with architects and interior designers of late. Burnished concrete is a Class A finish. The Gloss level is between 1-4 with level 4 being full gloss.
A Class A floor is achieved by a few critical steps. First the concrete when installed must be placed as level as possible as we are not removing any material from the surface. Any highs and lows will remain in the concrete. If your floor isn’t laid flat when you look across it, it will look like the ripple of an ocean.
When using the trowling machine (aka helicopter) the concreter needs to burnish the concrete until black, your concreter should understand what we mean by this term and this will start the polishing process. We arrive two weeks later to continue the polishing process. This will build up a thick crust and allow for the floor to be successfully polished. The concrete needs to cure for two weeks before the polisher can start working with it. If you use a higher MPA this can reduce the time however, we recommend using a minimum of 32MPA for a class A/burnished finish.
It is important that the concrete is protected before polishing. If you wait to have the floor polished then the polisher may not be able to remove the stains and marking left behind from building. This can mean that there is discolouration from tanins or dirt or rust on the concrete that cannot be removed by polishing and a heavier grind which will expose aggregate may need to be performed. By your polisher completing the works first they can get a better finish on the floor as walls are not in the way but also there is less change/risk that the floor has already been contaminated and stained. Once the floor is polished and sealed it is fairly resistant to most staining damage. It is important that the builder tries to protect the floor during the rest of the build. Each polisher will have a different protection system they recommend that is appropriate for that project.
However, the best way to protect the floor is to keep a clean job site. Prior to walls and a roof being erected simple cleaning/sweeping or blowing debris and contaminants off the concrete. Don’t leave nails and screws there to get wet and rust. Don’t store timber on there to get wet and leach tannin. If the site is muddy clean your boots before walking on the finished floor etc. Once walls and a roof are installed you can protect the floor by covering.
With a Class A finish (burnished concrete) you need to have a good plan in place with the builder and the polisher to ensure that the finish you desire is achieved.