WHAT CAUSES FAILURE WHEN PAINTING A CONCRETE SLAB

Source:www.stonediamondtool.com Date:2019/12/20 Read:306

Paints can do an excellent job of protecting and beautifying concrete slabs, but only if the concrete has been properly prepared prior to painting. Unpainted outdoor slabs have likely been exposed to dirt from foot traffic, acidic rain deposits, residue from trees, tire marks and other contaminants. Indoors, the concrete's pores may contain dirt, grease and even mold. Unless properly dealt with before painting, all of these conditions can lead to premature failure of a new coat of paint.

Time to Cure

It may seem like a smart idea to paint a new concrete slab before it has any chance to get dirty, but coatings experts have learned that concrete needs up to four weeks to cure before it can be successfully coated. While the new slab may be hard enough to walk across, it still contains a high level of moisture that must be allowed to escape. If you apply paint before that happens, the moisture's only method of escape is through blistering and cracking the paint -- which means the coating has failed, and must be removed before trying again.

Clean Before Painting

Many coatings manufacturers recommend etching a concrete slab with muriatic acid before painting. A concrete paint needs to bond within the porous surface of the concrete itself in order to form a hard, protective film across the top. That bonding cannot occur if the pores are clogged with efflorescence, dirt or grease. When the paint lacks a firm grip under the surface, it can flake off rather easily when it is subject to foot traffic. If the slab is in the garage, the paint may adhere to hot tire treads and be pulled off when the car drives away -- which means the coating has failed. The paint then must be removed, and the concrete should be thoroughly cleaned before repainting.

Dry Before Painting

If you scrub a concrete slab or use a low-pressure power washer before painting, it's important to let the concrete dry thoroughly before painting. It's also wise to schedule painting on days where rain is not expected. In spring and early fall, the concrete may get damp in the early morning or early evening, so ideal application times would coincide with full daylight hours. You can rent a moisture meter to confirm the concrete's moisture level is within the paint manufacturer's recommendations. If paint is applied when the concrete is too wet, the paint is not likely to bond well, and the coating will fail. The paint must be removed, and repainting should be scheduled for a drier day.

Paint Must Be Applied During Temperate Weather

If the mercury drops below 40 degrees Fahrenheit or rises above 90, the paint will not adhere well to concrete. But it's not simply the air temperature that matters; it's the temperature of the concrete itself. While you could use a precision thermometer to monitor the temperature of the concrete, common sense provides a pretty good measurement as well. Simply keep in mind that concrete under direct sunlight likely is a bit warmer to the touch than the air temperature. Read the paint label for ideal application temperature, and don't apply paint when it's too hot or cold.

Choose the Right Paint

For the best results, choose a concrete/masonry paint designed for use underfoot rather than an all-purpose house paint. A masonry paint is specifically formulated to bond below the concrete's surface, and a floor or garage paint contains additives that accommodate the continued rubbing and scraping of foot or vehicular traffic. It should also hold up better to spills, tire or furniture marks, and routine cleaning fluids. When applied to properly prepared concrete slabs, a concrete/masonry paint is much less likely to fail prematurely.