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Short Summary
Main recommendation: Before pouring floor leveler on bare concrete, clean and wet the surface thoroughly, prime it with a compatible primer, let the primer dry until at least tacky, then mix and pour a self-leveling compound that matches your flooring type. The speaker, Jeff from Ottawa Design and Build, is working on a basement bathroom subfloor and uses MAPEI products throughout, stressing that improper prep and mixing will lead to cracking, breaking, and noisy steps.
Key Points
- Choose the leveler by floor type: sandable leveler for sheet vinyl, a smooth, thin, workable leveler for tile, and only enough to fill dips and valleys for heated floors. For thick vinyl plank, the goal is to remove ridges and reduce valley effects.
- Buy all products from one supplier, since they are designed to work together. The speaker uses MAPEI's Eco Prime Grip primer and a MAPEI quick-set self-leveling compound.
- Aim for roughly 95 to 100% adhesion, which requires thoroughly cleaning mud and debris before priming (he says he's not looking for 75%, but more like 95 to 100%).
- Mix exactly to the product instructions; the speaker warns this is "like science," as the consistency changes dramatically with small amounts of water.
- Let the leveler set, then address any remaining high spots by chiseling them off rather than reapplying.
Details Worth Noting
- Concrete instructions: Clean the area with a sponge and water to remove mud, keeping the fresh concrete wet, then dab off excess water. Pour the Eco Prime Grip primer directly onto the floor rather than using a tray, and distribute it with a small nap roller, working it into corners and over the patch. Allow the primer to dry for about an hour, or up to two depending on thickness and temperature, using a fan to help; it should be at least tacky before leveling. Read the product label for mixing. For the 50-pound bag, the speaker's MAPEI product requires about 6 liters of water (5.88 exactly), which he says is tough to measure precisely on a job site. Measure water in marked pails, add the bulk of the water, then mix powder in slowly until it starts to come together before increasing speed. For first-time mixers, he suggests mixing the whole 50-pound bag at once in a pail big enough to hold it, rather than trying to mix partial batches, to avoid getting the consistency wrong. Pour the leveler toward the back of the room, spread it to fill low areas, and let it dry. Recheck the next day and chisel off any bumps.
- The speaker notes that the mixed leveler is quick-setting, so it should not be poured down a drain; clean tools promptly.
- Vinyl tile or thick vinyl plank may need only a rough, functional level, but tile jobs may call for sanding the edges. For vinyl, a second thinner layer can be applied without repriming, but he notes the primer must be present somewhere to ensure bonding.
- The speaker's goal in this case is a level base so the toilet does not rock once mounted.
Bottom Line
Proper cleaning, priming, and exact mixing are what determine whether a leveling compound bonds and performs, so the product instructions should be followed closely.
