A self-leveling underlayment is a good solution to resolve issues with an uneven concrete subfloor. As the name implies, it levels itself. Underlayment products come in plaster of Paris or cement-based powder formulas, which you mix with water or latex, depending on the brand. The mixture is poured on top of the subfloor and allowed to cure and harden. Curing time will vary from brand to brand. These types of products can only be applied to a floor with a concrete floor or subfloor.
Rapid-setting floor leveling compounds will take care of that problem floor in little time. However, this is another product that only works on concrete. Rapid-setting compounds live up to their name. Some will start to set up within five minutes, meaning that you will need to be prepared to get to work right away. Most rapid sets can be walked on in as little as two to three hours, which is another benefit because you will also be able to replace the top flooring material, such as tile, carpeting or wood the same day. You can find self-leveling underlayment powders in stores that sell carpeting and flooring and in hardware and home improvement stores.
If your problem is with a tile or hardwood floor, you can add strips of moisture barrier and foam underlayment to add height and level the floor. Like leveling compounds, these materials are also sold in flooring stores and are easy to work with. Purchase the thinnest material you can find so you can build it up to just the right height. You can cut the foam with scissors or a utility knife to get the shape and length you need for the uneven area and stack layers of foam, if necessary, to again make the tiled or wood floor area level. You can use a moisture barrier or foam underlayment on any type of subfloor — wood or concrete.
If you have hardwood floors, try two fixes that professional installers use — shims or roofing shingles. Take a long straightedge and place it at the highest spot on the floor. Then, get on your knees and glide the straightedge in a 360-degree circle. You will be able to see exactly where the floor is sagging and needs leveling. Mark the sagging area with chalk and pry up the wood boards. Then, you can insert shims to level out a sagging spot. Roofing shingles can be cut up to fill in dips or depressions. You can even stack them, if necessary, to get the right height you need under the wood floorboards. This technique is a quick and inexpensive fix andyou can use it to resolve problems with floors on a second level where the subfloor is not made of concrete and you can’t use a leveling compound.