Decorative Concrete – Dealing With Cracks
I was always told that there are five things you can count on when dealing with concrete. It will always get hard; it will change color; it won’t burn; nobody will steal it, and it will always crack. So, how do we deal with cracks before installing a decorative overlay?
Cracks in concrete can have several causes, and if left untreated they can get worse and possibly lead to significant structural damage. If they are not remediated properly before installing a decorative overlay, they will always look unsightly and cause problems later on.
There are two types of cracks that we should be concerned with: minor surface cracks, usually caused by shrinkage, and deeper structural cracks, often caused by movement in the sub-grade.
Surface cracks are easy to treat. Ignore the hairline ones and chase out the larger ones with a crack chasing wheel. The resulting groove can be filled with pretty much any rapid setting epoxy or cement product. We use QuickMender by VersaFlex. This is a two-part rapid setting epoxy that can be poured into the groove and left to set. After 20 minutes or so, the surface can be ground down level. QuickMender can be mixed with coloring pigments; it self-levels and has immense strength. It is unlikely that surface cracks will reappear.
Deeper structural cracks, on the other hand, can often reappear because they are the result of a structural weakness. They are often called cracks that want to be control joints. If we repair a deep, structural crack, it will often reappear unless we cut a control joint next to, or close to, it. Random control joints can often be disguised by integrating them with a pattern.
To fix larger cracks, we first of all clean up the edges with a crack chasing wheel and then fill the crack with silica sand. We then pour QuickMender into the crack until it is overflowing. As the QuickMender sets up, we work it into the crack with a scraper until it stops flowing through. After 30 minutes or so, it can be ground level with the surface.
Once the cracks have been repaired, we will discuss with our clients the likelihood of them reappearing and let them decide whether we should cut control joints in the finished surface.
There are many epoxy crack filling products on the market, and we have used quite a few of them. One problem we experienced was the bubbling up of the surface days after we had finished the project. This is caused by moisture in the bottom of the crack reacting with the epoxy. We tried drying the cracks out with a torch, but it would still happen occasionally.
Epoxy fillers are great if you are covering the crack with an opaque surface such as thinset or epoxy flake. They do not look good if you are just doing a grind and seal application. In this case, we will use Ardex SD-M which is a rapid setting cementitious product. This looks a little more natural when using a clear coating or sealer.