Concrete Skim Coat
Boys will be boys, right? Well, not so much for this irate Irving, TX homeowner. Seems like some of the neighborhood kids snuck into his backyard right after a contractor had poured the pool deck and decided to “personalize” it in several spots with their initials.
Not the smartest move on their part; they were quickly caught and reprimanded, but the damage was done.
The last thing on our homeowner’s mind was to tear out the pad, and we agreed; all we had to do was apply our concrete skim coat and bury the problem under a new, thin coating of concrete.
This thin coating of concrete, also called a skim coat, is especially suited for this type of work. In this case, as the concrete was new, we power washed it to remove the muddy footprints and then applied two coats of the skim coat material.
We wrapped it up by staining the floor to create a more variegated, marbleized look throughout. Once our material dried, we sealed it to protect it from the elements. All traces of their mischief were wiped away.
Proper surface preparation is very important during this process. Taking shortcuts here will almost inevitably lead to problems down the road.
Our skim coat material is robust; it will stick to almost anything (believe me, I’ve scraped the stuff off elbows and fingers up to a week later) but what we are looking for is long term durability.
If the floor is freshly poured and has a broom finish (thin lines running down its length that were made by passing a broom over the still drying concrete) then often power washing will be enough to properly prepare the surface, especially for areas that will only see foot traffic.
If the floor was painted or sealed, we almost always grind it to “open it up” so that the overlay will stick tightly to the floor, even after years of use.
One last point, by freshly poured we mean no less than 28 days but no more than one year. If we try to apply a concrete skim coat to a newly poured concrete slab (less than 28 days) we are asking for trouble.
As concrete cures it pushes out a lot of water that was part of the mix, if we put an overlay on top of that it’s like trying to put the cap back on a shaken up bottle of soda. That liquid just wants to get out and it will push on that overlay and try to pop it off. After 28 days, assuming it’s not in freezing conditions, enough water has pushed out that it won’t weaken the bond between our concrete skim coat and the original slab.
Sometimes a floor will have a previous coating on it like “cool deck” or an equivalent. What we do with this depends on how well adhered it is to the floor.
If it’s loose, then it has to come up. If it’s still stuck on tightly, we can apply the new skim coat overlay directly on it (after cleaning), saving our clients the cost of grinding it off. The one caveat is that our material is only as strong as what we are going over, so if the original coating were to peel off for some reason, then ours will.
To date (knock on wood) this has never happened, but it’s something we can’t guarantee won’t happen unless we take the additional step of grinding it all off.