No subfloor is perfectly level, but any signs of unevenness and high or low points must be corrected. Subfloors should not slope more than ½ inch per 6 feet (25 mm by 1.8 m). If your floor is concrete, use a concrete grinder for large, open areas or a 4- or 8-inch angle grinder with a wedge-shaped attachment made for use on concrete. When I arrived at the mezzanine, I saw that all the floor beams on the living room side of the house had been assembled and that 4 x 4 beams had been installed, with 2 x 4 posts supporting wood and soil.
It's worth repeating that floors are rarely level, and it's generally accepted that a slope of one inch in twenty feet is acceptable. To prepare a concrete subfloor for installing tiles, you will have to do another type of preparation. To level a subfloor to install the laminate, follow the instructions above to eliminate high and low spots. Use a subfloor product, floor levelers, or floor patches to repair low spots in a wooden subfloor the concrete.
To prepare a wooden subfloor for installing tiles, install a cement-based backboard following the manufacturer's instructions. No house has perfectly flat and level floors, but many have floors where the changes are so small that you don't notice them. If recommended by the manufacturer, go over the subfloor with a damp sponge before applying a floor leveler. I spoke to an inspector this week, who is hoping to file a lawsuit after revisiting a construction site to see a crowned floor.
Before installing a wood floor, follow the instructions above to fix the high and low spots in a wood or concrete subfloor. I would like to go back to that mezzanine and dig up to the foundation wall to see if the beams are supported on the foundation and if the ground and the wall structure are connected, all I think is that the floor is supported by a 4x4 beam that has been installed along the foundation wall and not on the base itself, which should be a little higher. Before installing a vinyl floor, follow the instructions above to fix the high and low points on a wood or concrete subfloor. Laminated planks stick together and “float” above the subfloor, meaning that small imperfections in the subfloor are fine; however, a level subfloor will help prevent damage.
Some people use a marble or ball bearing to determine if a floor is level, if that doesn't work on a carpet, if the marble is a specialized instrument.
