Preparation of Concrete for Applying Floor Coatings

Date posted: November 6, 2014

Proper preparation of concrete surfaces is essential before applying any coating system. Excessive moisture is one of two major pitfalls that cause the delamination in a concrete coating application. The other is, of course, inadequate surface preparation. Below is a step by step procedure for the ultimate preparation of your concrete floor:

Testing

1. Moisture control

The source of moisture can be found within the concrete, or it can enter from an external source. Newly poured concrete should cure for 30 days before coating application. This allows the moisture to fall to an acceptable level. A plastic sheet taped on the surface for 24 hours is a simple, but effective method of testing for moisture in the concrete. Any excess moisture in the concrete will condense under the plastic.

A moisture meter also can be used, and the best is one that measures not only the moisture percentage deep in the concrete, but has also a humidity box. It is placed on the concrete for a period and the hydrostatic humidity is measured, that is the moisture that may also be coming out of the concrete from underneath.

Moisture content should be lower than 5.5%.

The next step is to test for any contamination, sealants or previous treatment in the concrete.

2. Test for Contamination, Sealants or Previous Treatment

“The Water Droplet Test”

This test is where a few drops of water are placed on the concrete and if the water soaks into the concrete then the concrete should be fine for coating. If the water droplets “bead” on the surface of the concrete, then the concrete needs to be treated further. If oil is present in the concrete, preparation should be especially thorough, and A&I Coatings technical staff are available to advise in this situation. They have access to products that will force the oil out of the concrete.

Preparing

Diamond Grinding

We at A&I Coaitings recommend diamond grinding as the number one method of preparation. Diamond grinding is the most basic method of removing grime, contaminants and grease, at the same time opening the pores of the concrete so it is receptive to the first priming coat you intend to apply. For the ultimate adhesion of a concrete coating system, the primer coats penetration into the substrate is imperative.

See the Visual Standard for Grinding and other methods of surface preparation, below. Grinding should give a profile of CSP 2-3.

Cleaning, degreasing and acid etching

If a floor grinder is not at your disposal, the most important thing is that the concrete is clean, dry and etched. We advise that all concrete surfaces should at least be acid etched.

Concrete needs proper cleaning. Acid etching does roughen the concrete surface, but does not remove laitance or other loose material. When dealing with oil and grease marks, a degreasing agent can sometimes assist with its removal. Acid etching at one time was considered a completely reliable method of concrete preparation but now is considered only an alternate to mechanical methods, and is used only when no other methods are possible.

When acid etching, mix a solution of commercial grade hydrochloric acid 10%-20% in clean water. Phosphoric, sulfonic or citric acid can also be used. While hydrochloric acid is the most economical to use, and can be found at most hardware stores, it can leave a residue of chloride salts that, once formed, is hard to remove and can cause failure of the coating. Hydrochloric acid is also a potential health hazard. Acid etching works fairly well on non-surface-hardened floors and other horizontal surfaces but is very difficult to use on vertical surfaces.

Hose down the concrete, and allow to dry. Apply the etching solution liberally over the concrete, and brush over, ensuring any oil spots, stains or chemical spills are especially given a hard scrub

Immediately after scrubbing, hose down the concrete flushing it completely clean of any acid and chemicals.

Do not allow the acid etch to dry. Residual acid or chemicals will result in reduced performance of your floor coating. After thoroughly rinsing, allow 1 day for drying.  Give the concrete one last sweep to remove any dust and debris.

Lastly, ensure that the floor surface is clear, dust-free, clean and dry before mixing the basecoat for priming.

Water blasting

Water blasting is only a last resort. If water blasting is the only option we recommend the water droplet test to be done once the concrete has dried from water blasting. This test is where a few drops of water are placed on the concrete and if the water soaks into the concrete then the concrete should be fine for coating but if the water droplets bead on the surface of the concrete then the concrete needs to be treated further. If oil is present in the concrete, preparation should be especially thorough, and A&I Coatings technical staff are available to advise in this situation. They have access to products that will force the oil out of the concrete.

Repairing

Concrete will crack due to a variety of factors, including moisture content, lack of reinforcement, no expansion joints, excessive heat, movement in foundations/unstable ground, and excessive weight or force. Flexible polyurethane sealants such as “Sikaflex”, can be used to seal and conceal joints, as well as compensating for the natural expansion and contraction of the concrete.

Crack repairing compounds can mixed up using a high build 100% solids epoxy “Envirothane 4111” (view the E4111 product data sheet here) mixed with sand, and trowelled on.

A&I Coatings understands the importance of proper concrete preparation, and our helpdesk team offer expert advice on request. We also have many types of high-performance coating systems suitable for a variety of substrates. Contact us today with your requirements.