Q. I am going to glue some fiber reinforced polymer on a concrete beam, but I'm concerned that some oil spilled on the beam may prevent the epoxy glue from adhering well. How can I remove oil that has been spilled on the concrete?
A. One of the easiest things to try first is brushing some dry portland cement into the surface, but that can go slowly. You can make a poultice by mixing mineral spirits with any of several fine powders—kitty litter, Portland cement, talc, or diatomaceous earth—and apply that to the stained area. Allow it to dry; then remove and repeat as necessary.
You could also try the products offered by Practical Environmental Solutions (www.pes51.com). The company's hydrocarbon bioremediation products include microbes to actively remove the oil that has gotten into porous surfaces such as concrete. A citrus-based cleaner/degreaser or even a laundry detergent that includes a degreasing agent are some other alternatives.
Once you have removed a sufficient amount of the oil, remember to prepare the surface for the adhesive by mechanical roughening or by using a little muriatic acid.
Q. I am the lead of a building committee at a school where we are building a new 6000-square-foot gym that will have vinyl tile floor covering. We are installing ?-inch PEX tubing for hydronic heating in the 5-inch-thick, 3000-psi concrete slab. My major concern is surface cracking that will affect floor quality. There appear to be many opinions on a lot of different aspects of such a project. What should we focus on?
A. Surface cracking and moisture are both valid concerns when installing a slab on grade that will be covered with vinyl flooring. Fortunately, experienced professionals can deal effectively with these issues.
While installation techniques are important, one key ingredient is a good concrete mix design. The mix should have well-graded aggregate and a low water content to minimize shrinkage cracks, which means that some superplasticizer may need to be added to enhance workability. Beyond that, two other factors relating to moisture are also very important. Because you will be covering the slab with vinyl flooring, you should place a vapor barrier (minimum of 10 mils thick) immediately below the slab—on top of the granular base material. Make sure you use a low-permeance vapor barrier rather than a vapor retarder; it's worth the extra money.
You should also make sure that the concrete has dried sufficiently before the flooring is put in place. Don't rely on waiting a certain predetermined time. Insist that moisture tests are done on the concrete slab and that your flooring contractor agrees that the moisture level is sufficiently low before proceeding with the flooring installation. Wagner Electronics and CTLGroup introduced a new relative humidity meter at this year's World of Concrete that you might find helpful. You can get details at www.wagnermeters.com.
Including hydronic heating in concrete slabs is becoming more widespread. It should not have any adverse effect on the finished slab, and should provide you with good comfort in the future. For more information on that aspect of the project, visit www.radiantpanelassociation.org.
Regarding the vinyl tile, we passed your question on to Dennis Bradway, manager of technical support for Mannington Mills, a manufacturer of resilient floor coverings. He says that from the manufacturer's perspective there are three items to watch. First, the surface temperature of the floor should not exceed 90° F. Before the floor covering is installed, the slab and cementitious topping should have dried to the level recommended by the floor covering manufacturer, and any surface cracks should have been properly patched, level and smooth, using a quality cementitious patch.
We also talked with Howard Kanare, of CTL Group, who has done a lot of work on moisture issues with floor coverings on concrete slabs. Kanare says, “I would add only that the floor system should be placed as early as possible during construction so that the concrete will have time to cure, dry, and shrink. Then, cracks can be patched and the flooring installed. The concrete mix should be designed to have ‘minimum shrinkage' using a moderate cement factor, moderately low water-cement ratio, and well-graded, large, coarse aggregate (not exceeding one-third the thickness of the floor slab), or even a shrinkage-compensating mix. The ready-mix concrete supplier can offer choices of mixes.”
Be willing to pay for good material, and then make sure tests are done (test cylinders, measuring air content) to ensure that you've gotten what you paid for.
Aggregate Research Industries
Aggregate Research Industries' Web site (www.aggregateresearch.com) includes topic-specific forums where forum members can pose questions and respond, creating an interactive discussion group. The first question and answer in this Problem Clinic and the one on p. 48 are based on ARI concrete construction forum postings.