Steps for Building on an Unlevel Floor

Self-Leveling Compounds

• One step you can take if you are working with wooden or concrete subfloors that are out of level is to use a self-leveling compound. Cementitious in nature, these compounds are mixed together with water to create a soupy liquid that is poured into the low spots in a floor and then allowed to level themselves as the water within the mixture does what gravity always does with liquids: self-level. Once things are hardened, you can then build on top of the now-level floor.

Grinding

• Grinding down the high spots is another step you can take to building on an unlevel surface. For concrete floors, you need a floor chipper that has carbide or diamond-tipped grinding blades in the worst cases, or an 8-inch cup wheel angle grinder for small areas. For wood floors, you can use a belt sander in small areas or a floor grinding machine with heavy-duty sanding pads for large areas that need to be sanded down to make the entire floor level.

Shimming the Floor

• If you are dealing with a wooden subfloor that is excessively out of level, such as in an existing home that has sunk into the ground over time, one of the best methods is to shim a new subfloor section. Basically, you trim down 2-by-4 material into long shims that stretch across the low spot on top of the old floor joists, going from nothing to the height you need them to be for the new subfloor, and then the new plywood floor is installed on top, creating a level base. Essentially, the shims are ramps that help build up the existing joists to level.

Floating Up

• Another method to fix a subfloor that is excessively out of level is to use what is known as a "mud float." Essentially, this is a concrete-and-sand mixture that is packed into a damp-sand format and then floated level across the surface. Generally these mud beds are 2 to 3 inches thick and are most common with ceramic tile and natural stone installations, but they can also be used to create a base for floating wood floors or even carpet floors.