If you are installing a subfloor over concrete, there are several problems that you could run into. This process is commonly done to provide a subfloor to attach hardwood flooring. Consider the following common problems that may arise when you attempt to add a subfloor over concrete.
Choosing the Adhesive
When you attach plywood to a concrete subfloor, you will need to make sure that you get the right type of adhesive. Many people purchase the wrong kind of adhesive for this project, and the plywood ends up coming off the floor.
Spreading the Adhesive
When it comes time to apply the adhesive to the floor, you must take care to do it properly. The adhesive is very thick, so you have to use a trowel to apply it to the floor. Take your time to ensure that the adhesive is adequately spread.
Doors
Another problem that many people have is going through a door with the subfloor. If you have connecting rooms, you will need to cut the plywood to fit in the doorways. This can be difficult for many people, and it takes some patience and skill to cut it properly.
Source: www.DoItYourself.com