Perfect subfloor, perfect end result

Pretreatment of floors

The quality of the floor finish stands or falls with the quality of the substrate. Especially when installing flexible and delicate floor coverings such as vinyl, carpet, PVC or marmoleum, a level base floor is a must. Indeed, "The screed cannot be perfect enough," believes Luc Wouters, Technical Account Manager Flooring at Bostik. "To achieve this, the right technical pre-treatment is essential. Is the subfloor sufficiently clean, dry, normally porous, firm, crack-free and flat?" In order to achieve a quality, mirror-smooth subfloor in every project and in every circumstance, Bostik is happy to conduct a comprehensive site survey. For example, to arrive at a step-by-step plan and extensive advice.

Floorers who install a finishing floor already take over responsibility for the subfloor when the first square meter is installed, Wouters knows. "To eliminate risks, it is important that they go through a number of steps, which Bostik is happy to support them in."

1. A clean floor

To ensure good adhesion, it is important that the substrate be free of impurities, he knows. "Paint residue, plaster residue, sinter skin, glue and varnish can be removed from the substrate by sanding, for example. Then it is important to brush and vacuum the substrate thoroughly."

2. A permanently dry surface

In order to estimate whether a substrate is sufficiently dry, the residual moisture content must be determined. "Bostik uses a digital moisture meter (indicative moisture measurement) and a Carbide Measurement for this purpose," Wouters says. "In the latter, a sample/sample of the substrate is taken at least 5 cm deep and mixed with an ampule of calcium carbide in a carbide meter. The pressure created by the gas formation is displayed as a moisture percentage on the meter." For a cementitious screed, the maximum residual moisture content is 2% without underfloor heating, he adds. "With underfloor heating, the residual moisture content should be a maximum of 1.8%. Should a cementitious screed contain too much residual moisture, a two-component epoxy moisture barrier such as Bostik HYTEC E336 XTREM should be applied."

Particularly in buildings on full ground and without a crawl space or in the case of tile floors, rising damp can occur. "Especially in old houses, where there is no plastic sheeting under the floor. Therefore, such buildings should always have a moisture barrier that can resist compressive moisture."

3. Understanding porosity.

To test the porosity of a substrate, a drop test can be performed. This involves applying a few drops of moisture and then measuring how quickly the drops soak into the substrate. "If the penetration is shorter than one minute, then the substrate is (too) porous," Wouters said. "In this case, a special adhesion primer such as Bostik GRIP A500 MULTI can eliminate the suction of the screed." For closed substrates, a primer such as Bostik GRIP A936 XPRESS is more suitable.

4. Good surface strength

Good surface strength (compressive and tensile strength) of the screed is also a requirement. "For tensile strength, it should be at least 0.5 N/mm2 (preferably 1 N/mm2 for parquet floors)," Wouters says. "The compressive strength of the substrate must be higher than 8 N/mm2. If the floor is not strong enough, a special screed stiffener can be applied. In addition, the substrate must not be (too) granular, powdery, pliable or flexible." If the substrate does not meet the requirements, then it is important to reinforce the substrate with Bostik HYTEC P510 RENORAPID, for example.

5. Tear-free base

Existing cracks and cracks in the substrate must also be repaired. This can be done by grinding out the cracks, applying staples and filling the cracks with a two-component silicate resin, such as Bostik RENO P520 EASY or by applying two-component epoxy resin Bostik RENO E742 STRUCTURE.

The right leveler for every situation

Once the above steps are completed properly, it's time for the primer and leveler. "The leveling compound is used to make the floor nice and flat," Wouters said. "Which leveling agent is best to use for this purpose depends mainly on the use of the room, the type of screed, the desired pressure resistance, the maximum layer thickness and the drying time. Following on from the standard levelers, floor finishers can contact Bostik for fiber-reinforced levelers, such as Bostik SL C740 FIBER MAXI for flexible (wooden) floors. But also for quick-drying levelers such as Bostik SL C990 SPRINTER, which can be worked on as early as 2 to 4 hours after application. If high compressive strength is desired, we recommend Bostik SL C980 XPS, with a compressive strength rating of C40. Also very popular is our Bostik SL C940 XL smoothing compound, with which a height difference of 50 mm can be bridged. The selection of the right products is a standard part of our advice. On request, we also provide product and application training. Both at our own location and on site, ensuring proper application."