Concrete spalling is often caused by improperly placing the rebar or wire mesh when pouring the concrete. If the rebar is to close to the top of the concrete slab, as water soaks into the concrete it will start to corrode the rebar. This will cause the rebar to expand, weakening the concrete above the piece of rebar.
If you look left of the blue line, you will notice there is a crack starting to form, this crack is right above a piece of rebar corroding. When we tap the concrete with a hammer we hear a hollow sound. To repair this we have to break out all the loose concrete, cut 90 degree edges, pressure wash & clean the rebar, and apply a non-shrink repair mortar.
Spalling Concrete Cause By Corroding Rebar
Right after we start to chip out the bad concrete a piece of rebar started to stick out. This was the main cause of the damaged concrete. It is very important to place rebar and wire mesh at the proper place when pouring concrete.
Spalled Concrete Area Chiseled Out
Concrete Resurfaced & Stained
After the concrete was chiseled out we applied Miracote RM 2 and then finished of the spalled concrete repair by resurfacing the area with Miracote MPC, and then applied a grey stain to match the bricks.
When concrete is in very bad condition cosmetically, the easiest way to repair the concrete is by resurfacing it. Concrete resurfacing involves: grinding the concrete to acheive a proper surface profile so the material will bond to the existing concrete, we then apply a base coat, and then a smooth coat or another base coat (depending if you want it rough or smooth).
The patio we worked on this week had a lot of things wrong with it. The first thing was it was very rough with a lot of pits that had to be repaired. We then ground the concrete to prepare it for the resurfacing material and to even out the construction joint where the two slabs butted up to each other. After resurfacing the concrete, we applied a stain and sealed the concrete. Once the patio was sealed we came back and re-scored the construction joint and filled with a self-leveling polyurethane.
There isn’t just the option of tearing out and replacing old worn down concrete. You have the option to use a modified-polymer cement to resurface the concrete, just as long as the concrete is structurally suitable.
Typical concrete resurfacing applications are used for restoring concrete that has been eroded, coated with a paint that is peeling off, concrete with a bad surface finish, concrete with shrinkage cracks, and spalled concrete. After the concrete has been resurfaced it can then be either sealed the way it is or the concrete can be stained using an acid stain or dye.
The proper steps for resurfacing concrete to insure a good bond are:
Grind concrete to produce a profile
Resurface concrete with a rough coat
Resurface concrete with a smooth coat or rough coat for a second time
After resurfacing cement has dried sand area smooth
Acid stain or dye the resurfacing cement
Seal resurfacing cement
Concrete resurfacing can be done inside and outside and the product we use is very durable for heavy traffic applications such as retail stores and parking garages. It can be applied with ether a smooth finish, skipped troweled finish, or a sand finish for exterior applications.
Pitted concrete is being resurfaced before acid staining.