Spalling – What it is and what to do

June 13, 2011

Have you ever seen this on a foundation before?

foundation repair services in Austin, TX

The rebar showing in this Austin home is called a “concrete spall” Basically this situation happened because the rebar in this concrete slab was too close to the surface of the slab edge and it started to rust because it was getting moisture and oxygen.

The rust is a growth on the surface of the steel and because of this growth, the rebar is getting fatter and the rebar requires more room to expand. The expanding steel causes the concrete to crack, break and delaminate the area around the rusting steel. Many times just a little rust can cause the first cracks in the concrete surface, but then the rust growth can really pick up speed as water and air enters the small cracks and feeds the rust, which I call “cancer” to the steel.

In Austin, the climate is fairly dry, and there is no salt air from the ocean so the rebar can take a long time to cause spalling to happen. In this case, the slab edge was getting wet from years of sprinklers feeding the problem.

The solution to a spall, is to review if the steel is needed to structurally support the foundation or if it is not. In this case, the steel is multiple layers of overlapping rebar and the bar close to the surface is redundant and can be cut out. The other bars are going to have to be cleaned to bare metal. All rust has to be removed.

To remove the rust, first chip away all loose concrete around the rebar and chip the solid concrete to expose the entire rebar as best as possible. Grind, wire brush or hammer off all the rust on the rebar. The rebar will need to be coated with an epoxy paint to seal the steel from any moisture or oxygen. At that time, the concrete can be patched with a quality mortar patch with vinyl adhesive added for strength and adhesion to the existing slab. Care should be taken to keep all sprinklers from watering the sides of our concrete slabs as the water causes damage to siding, bricks, stones and concrete.

Do you have questions about your Austin Foundation – Slab on Grade or Pier & Beam? Douglas Foundation Repair of Austin is your home’s foundation doctor. Call today! 512-291-0709.