Best Practices for Successful Surface Prep

By Emily Brunner

Surface preparation is one the most important steps in floor construction profitability. To help control this variable and increase margins, here are five best practices.

Plan Ahead and Communicate
Don’t skip essential planning. Before getting to work, share findings with the project owner and show them the value of well-planned surface prep. Stress that even though proper preparation might increase the initial cost, it will yield a higher quality, longer lasting floor.

Communicate the importance of proper surface prep in two ways. First, if a commercial project, a flooring installation failure could force temporary closure of their business, not to mention additional repair costs. If a residential project, they might have to pay for an entire new floor. Next, show the owner photos of failed flooring installations to emphasize the consequences of improper surface prep.

Firsthand Inspection and Documentation are Essential
Due diligence involves a firsthand inspection of the subfloor and documentation of any potentially problematic conditions. The amount of necessary floor preparation will depend on the flatness and/or levelness of the entire floor.

Conduct a pre-walk inspection of both the subfloor and overall structure. Bumps can be dangerous, especially in healthcare facilities. Look for holes or voids in the subfloor through which newly placed material might leak from above. Check the surface for any contamination by scraping it with a knife blade. A fine powder indicates laitance. Use a hammer or other heavy object to detect weak or hollow areas in the subfloor and note them. Sprinkle water onto the surface. If the water forms droplets without absorbing immediately, the surface is non-porous and may have contaminants that need to be removed. Shot blasting is an effective way to mechanically remove contaminants from the surface of concrete.

Avoid bidding the project before documenting any potential problems and adding them to the estimate. A typical estimate should include subfloor cleaning. This entails grinding, scraping, shot blasting or other methods to remove surface contaminations. Sweeping or vacuuming dust or other contaminants may also be required. Incorporate a clause for cost adjustments for subfloor conditions.

Thoroughly Clean Subfloor for Underlayment
Once the estimate has been approved, determine how much surface prep will be necessary given the new floor’s service requirements and its environment. The subfloor must be properly cleaned, level, dry and structurally sound.

Proper surface prep ensures the subfloor, underlayment and flooring material perform as a well-integrated system. Flooring materials like floating carpet tile and homogeneous sheet vinyl require vastly different surface prep. Follow manufacturers’ recommendations.

Facilities such as hospitals or laboratories likely need more surface prep than retail facilities, for example, to meet floor flatness tolerances. Consider the type of facility and flooring material to be installed, its strength and flatness requirements, smoothness and point loads on the new floor.

Note that old cutback adhesive may contain asbestos, so mechanical removal of this material by sanding, grinding or blasting can be hazardous. If gypsum plaster or joint compound is found, scrub the subfloor with warm water and detergent. Completely rinse off any residue and allow the concrete to dry.

For weak or damaged concrete, shot blasting or other mechanical means are required. Laitance will prevent a bond with the underlayment in these areas. A mechanical removal method, such as sandblasting or shot blasting, will also need to be used for paint that is not easily scraped off. Utilize these methods instead of chemical strippers on subfloors coated with paint.

Always remove surface dirt and dust using an industrial vacuum. Sweeping creates airborne silica that can lead to silicosis, a long-term lung disease caused by inhaling large amounts of crystalline silica dust. Avoid sweeping if possible.

Moisture Control is Paramount
Moisture control is necessary to ensure the long-term structural integrity of the floor. Use a properly calibrated moisture meter and follow the instructions to obtain accurate readings.

Commonly known as the in situ test, ASTM F2170 measures relative humidity within concrete slabs. Although this test has a higher initial cost, it is faster and considered more accurate than ASTM F1869, commonly known as the calcium chloride test. As a result, ASTM F2170 appears to be emerging as the industry standard. It provides results according to the moisture vapour emission rate.

If necessary, photograph job site conditions and record moisture testing results to prove proper steps have been taken to control moisture in the new floor.

Self-levelling Underlayments need Special Attention
Self-levelling underlayments require a few additional surface prep considerations. One is ensuring moisture mitigation takes place prior to installation. Check with the floor covering, self-levelling or adhesive manufacturer to determine if this is necessary.

The majority of self-levelling underlayments require that the subfloor is free of bond-inhibiting contaminants, such as oil, grease, dust and paint.

Remember to plug all floor openings, gaps and cracks and install termination dams to hamper material seepage. To prevent the transference of cracks in the finish, evaluate and isolate areas around walls, columns, penetrations and other building structures subject to movement to protect the adjacent flooring system.

Self-levelling underlayments require the use of a primer prior to installation. Primer retains the moisture within the self-levelling underlayment to facilitate proper curing. It also bonds the self-levelling underlayment to the subfloor properly. Use the primer the manufacturer recommends. Not doing so may result in installation failure.

Most self-levelling underlayment manufacturers recommend determining the substrate porosity for purposes of choosing the appropriate primer. This can be done with the ASTM F3191 water droplet test. If the substrate is porous, dilute the multipurpose primer. However, if it’s non-porous, use the multipurpose primer at full strength.

Emily Brunner is an area technical manager at TEC Installation Systems, which provides floor preparation and installation products for tile, stone, wood, carpet and resilient flooring. TEC products are available throughout Canada.

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