How to conduct pre-installation inspections to prevent future failure
When Benjamin Franklin famously said, “An ounce of prevention is worth a pound of cure,” he certainly wasn’t describing the process of installing tile over concrete. But he could have been, because properly evaluating and preparing your concrete substrate prior to laying tile will prevent countless – and costly –post-installation problems. Here are two tips on how to evaluate and address a few common conditions pre-installation.
1. Check for surface coatings and/or contamination
First, check the surface for any surface contamination. Scrape off any lumps and loose material. Then use an appropriate cleaning method for that particular type of contamination.
If you encounter gypsum plaster or joint compound, scrub the substrate with warm water and detergent to remove. Thoroughly rinse off any residue and allow the concrete to dry prior to the application of any TEC® materials.
Paint that is not easily scraped off should be removed by a mechanical preparation method such as sand blasting or shot blasting, which is one of the most effective methods of removing a wide variety of contaminants from concrete. If the substrate is coated with paint, then chemical strippers should not be used. They may leave a residue or be absorbed into the concrete and later migrate to the surface, causing a bond failure.
To remove an adhesive from a surface, first scrape it off. Then remove the layer of adhesive-contaminated concrete by a mechanical method such as shot blasting. Be careful; mechanical removal of cutback adhesive by sanding, grinding or blasting can be hazardous since old cutback adhesive may contain asbestos.
2. Address a weak top layer
First, scrape the surface with a knife blade. If this produces a fine powder, then laitance is present. Next, use a hammer or other heavy object to sound out weak or hollow areas. Note the areas that are weak or damaged.
Weak or damaged concrete must be removed by mechanical method such as shot blasting. If this step is not taken, the laitance will prevent a strong bond from forming – resulting in possible bond failure.
3. Ensure that your substrate does not suffer from invisible contamination
Sprinkle water onto the surface. If the water forms droplets without absorbing immediately, the surface is likely contaminated. Contaminated concrete must be removed by shot blasting.
Solvents should be avoided. They can drive oil, grease and other contaminants further into the concrete, only to release back to the surface at a later time. Oil-contaminated concrete must be removed to ensure a clean substrate and a proper bond.
Acid washing or etching is not recommended because it is difficult to fully remove contaminants and properly neutralize. The acid can penetrate into the porous concrete and chemically undermine it, weakening the concrete. Acid washing will not remove grease or oil.
4. Check for surface dirt and dust
Wipe the surface with a clean, dark cloth. If powder is visible on the cloth, the surface is not clean enough.
Always use a two-step method to remove surface dirt and dust. First, use a dry clean broom and sweep the entire surface. Do not use sweeping compounds as they can leave an oily or waxy film on the concrete surface that will prevent a proper bond. The second step should consist of one of the following:
- Vacuuming—use a heavy-duty industrial type vacuum to provide a dust-free surface.
- Water cleaning—use a stream of potable water with sufficient pressure to remove dust and dirt. When necessary, also scrub with a stiff bristled brush. Thoroughly remove all wash water and allow concrete to dry prior to application of any TEC® materials.
- Detergent water cleaning—Using a stiff bristled brush or broom, scrub the entire concrete surface with a cleaning product intended for concrete or a solution of at least 4 ounces of trisodium phosphate per gallon of warm water. Before the surface dries, thoroughly flush the concrete with clean potable water to remove all wash water and residue. Allow concrete to dry prior to application of TEC® materials.
Time is a precious commodity. But taking extra time to carefully inspect the substrate will prevent frustration and delays during installation. Ensuring the surface is properly conditioned will help prevent future issues such as bond failures.
If you need assistance determining which product is right for your job, contact our Technical Support team by here or by calling 1-800-832-9023, Mon-Fri 8 a.m. - 6 p.m. CST.