What’s happening in this video…A large military aircraft hangar floor being prepared by a shotblast machine to create a rough profile and remove any loose or powdering concrete so the specified coating system has a strong bond to the substrate.
This ride-on shot-blast machine is a floor preparation method used to cover very large areas in a short amount of time.
The metal “pads” which continually blast the floor to create the deep profile, wear down during the process and the steel shot are vacuumed up by the machine at the same time.
However, some of steel shots escape the vacuum and as you can see here are then swept up using a magnetic sweeper.
Floor preparation is the key to a successful floor coating application for longevity and protection of the concrete floor surface.
Frequently asked questions about preparing concrete floors for coating…
What methods are taken to prepare an aircraft hangar floor for a coating system application?
A mechanical surface preparation is preferred for most floor coating systems. The equipment used is a shot blast machine, and it utilizes an alloy wheel containing steel shot beads that spins with a high magnitude of centrifugal force on the concrete floor surface.
It’s very important to select the right size steel bead. If you’re applying thin mil coating products, you want to use a 110 mesh size, but if applying a high build coating, step that up to a 330 mesh size.
If the floor coating is something in between 20 and 60 mils thick, a mixture of 110 and 330 mesh size is customarily used.
If you create too rough a profile peak to valley ratio (picture concrete mountains and valleys), on the concrete floor and you apply a thin mil floor coating system, you’re going to have peaks telescoping through the coating.
Ultimately the peaks will accumulate surface contamination. This is the first area where the concrete floor coating starts to fail. This is not a good thing. These areas are prone to harboring bacteria and where the coating will start peeling away.
When shot blasting in preparation for a 3 mil sealer for example, it is well to stay within the International Concrete Repair Institute (ICRI) guideline which indicates a given concrete surface profile (CSP). In this instance, nothing higher than a CSP3 is recommended.
If you are applying a high build coating which would be more suitable for an aircraft hangar floor, a high build floor coating is around 10 to 40 mils thick. You are going to still use a CSP3 specification.
When you get into self leveling floor coating and resurfacing systems that are generally 50 mils up to an eighth of an inch, you would increase to CSP4.
This profile is a deeper valley on the floor, giving more “teeth” for a better mechanical bond for the coating system. Again, this is in keeping with the ICRI Surface Preparation Guideline.
Floor condition testing and evaluation
Of course, when you get into polymer overlay floor coating system, an epoxy mortar or a cementitious urethane mortar, these types of products can go anywhere from a quarter of an inch up to half an inch in thickness on the concrete surface. And you are going to have to increase the CSP to CSP5.
Keep in mind that there should be an overall floor evaluation of the floors surface. Moisture testing is also very important. Follow the guidelines of ASTM 1869, also called the calcium chloride test.
Many contractors and installers refer to it as the puck test because the tests apparatus looks like a hockey puck. In this test a plastic shield is taped to the floor with a little dish beneath the shield to collect moisture over a period of time.
At the conclusion of the time period, the pellets in the dish are weighed and compared to their weight before the test. The results will be the pounds per thousand per 24 hours of moisture pressure in the slab.
If over a three to a four reading on the slab it is likely a moisture vapor barrier will be required. In other cases a cement urethane comes into play. These systems withstand anywhere between 12 and 14 pounds.
The calcium chloride test is only a snapshot in time or what’s happening on the slab at the time of the test. Further evaluation may be required at different times or even seasons. This is where an experienced coating contractor can provide guidance to the building owner.
Crack and joint repair is essential for a smooth coated surface
After proper surface preparation of the aircraft hangar floor, the next step is to take a look at fixing the cracks on the floor. Fixing cracks is a bit misleading since there is no way really to fix cracks in concrete. It’s only to fill them. You can never fix a crack.
So, the proper term we use when treating cracks is “bridging the crack”. So what we are trying to do is bridge the cracks, those hairline cracks that you see all over the floor, in some cases, not in every case. Prepare cracks for repair by using a crack chaser with a diamond blade.
A crack chaser is going to remove any loose concrete that’s in the crevices. It’s going to strengthen the crack as much as possible. And then you have to select the proper repair material to fill the crack.
The material has to bond tenaciously to the concrete surface. And you are going to feather it about two inches away from the crack itself, right on the surface.
Always put a little bit more material on the crack crown. After application, the crown will be sanded down. The crack filling material must be compatible with the top coat and ideally 100% solids material in the medium viscosity range, about 800 to 900 centipoises.
Proceed to patch all remaining bug holes and shallow depressions and level out the floor as much as possible. The coating will not accomplish this so the best surface prep prior to coating is vitally important to achieve a uniform and visually appealing flooring surface.
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