Liquid floor leveller is a very thin, watery form of cement that's used to fill in cracks, holes, dips and uneven surfaces on underlayment before you lay flooring materials. It's good for patching up both cracked cement and the seams between plywood underlayment, in preparation for either clay, stone or vinyl tiles. Since liquid finds its own level, the leveller naturally evens itself out when it's poured, filling in the low spots. It has a very fast initial drying time (10 to 15 minutes), so it's important to do small sections at a time.
Get the floor clean and dry. Go over it with a vacuum to ensure that all loose dust and debris is extracted from the surface.
Mix your floor levelling compound in a bucket with water at the ratio recommended on the packaging. Generally, the leveller should end up with a very thin, soupy consistency, almost but not quite liquid.
Pour the leveller over the floor starting in a far corner from the doorway and working your way out. Do areas of about 3 by 3 feet at a time. Guide the levellers into the cracks or valleys as you pour it, using a trowel. Scrape a 2 by 4 over it, to get it smooth and level with the surrounding floor.
Do the whole floor, in sections. Let it set overnight.
Lightly sand the surface of the floor with a vibrating sander and 100-grit sandpaper. Vacuum up the dust.
Wear a dust mask when sanding the dried leveller.