Diagnosing Concrete Problems

Levco has been  asked to diagnose concrete problems with regularity. Whether it is foundations, slabs, or other, concrete,we are seeing the same issues  consistently.  I have researched the issues and  gathered the information needed to understand the more common ones. We also have extremely knowledgeable resources to assist on the less common issues.

First of all there is a clear difference clear between cement and concrete. Cement is the material that is considered the binder that causes concrete to form “Concrete is the hardened version of Cement.” Portland cement also known as a hydraulic cement, is made from mined materials that are combined and baked at high temperatures. It is then dried and ground into a fine grey powder. The reaction  occurs when water is added. The reaction is exothermic, in other words it dries by way of chemical reaction and can actually dry underwater. The list of problems is long but  group nicely into several categories.

Cracking: Often caused by poor sub structure preparation. This could be from shifting soils, improper reinforcement, or other unknown forces. It is often said that there are only two types of concrete…”That which is cracked, and that which will be cracked”

Surface Blemishes: This includes damages by salt deicing applications, over finishing when installed, and damage caused by cold weather during installation (over hydration of the mix). Efflorescence is another surface blemish caused when water passes through the concrete and carries dissolved salts and minerals that evaporate on the surface leaving unsightly mineral deposits.

Disintegration or failure: Too much pressure causing crushing or over stressed materials. This could be caused bu poorly mixed materials or a weak batch. (Often seen in home mixed materials)

At Levco, we have learned that it is rarely worth it to pour our own cement. For one, the large suppliers only like to serve the subcontractors. Secondly, the subcontractors with experience do a better job, I feel that it is one of those things that needs to be done frequently to be great.

Once a problem has been identified we occasionally need to do a destructive analysis to determine the severity of the problem.

Case Study: This issue arose during preparing a concrete slab in an old one car garage that we were evaluating for tile overlayment. Our installer was grinding things flat when he noticed that the concrete was disintegrating below his grinder. Worried he called a pow pow with his mastic sales representative myself and Diane the project manager. It just so happened the owner arrived in time to meet with us. After tapping on the slab we noticed a distinctly hollow sound over much of the slab. It became obvious that there was substantial deterioration and that no substance would make up for a proper slab. Surgical removal of portions of the slab was not practical so the decision was made to remove and replace the slab.

Carefully cutting 4″ away from the edges we removed the remains of the slab and discovered that it had no substructure in other words it was built without reinforcement on the dirt. It also crumbled onto sand and stone as we hit it with the jack hammer.

My suspicion is that the freeze thaw cycles of the past 80 years ruined it along with the suspicion that a light mixture of cement was used.

In replacing the slab we dug down an additional 4″ added drain rock then a layer of 3/4″ road mix and compacted it then a layer of moisture barrier and doweled in 3/8″ re-bar supported to dwell in the 4″slab as described in building science.com. We used a cool product called Schluter Ditra mat as a substructure to the floor tiles as a isolation membrane for an installation we can stand behind.