What kind of failures? So many that we have separate subject pages for each condition. More links can be found at the bottom of the page.

Terms and Recommendations

Too often many confuse level with subfloor condition. We want FLAT. Flat is what you want for a suitable subfloor. For now we'll have to use the term level because many use it and don't understand the difference. What better way of showing how to find if your subfloor is flat with pictures(shown below). By using the straightest board you can find, preferably in the eight to ten foot range, move it around on the subfloor in all directions looking for high and low spots.

In our picture above, one end of the straightedge is on the concrete subfloor while an area of about six foot is actually lower. For successful installations, hardwood manufacturers recommend your subfloor be flat with any tolerances greater than 3/16" in ten feet be corrected.

For concrete subfloors a fast drying compound is used to screed (shown bottom left) over the low spots. High areas may require actual grinding of the concrete. Grinding can be extremely messy unless a wet grinder us used. Our only problem with this procedure is the moisture that is dumped onto the subfloor. For any successful hardwood installation moisture content should be monitored. In this case grinding well ahead of the actual installation should be considered to allow the subfloor to dry properly.

Wood subfloors require different methods with the primary method of sanding down higher areas. Most professionals use a hardwood flooring edger that can be rented at most home centers. Edgers have more power and can take down high spots much quicker than a standard belt sander. Ask for the coarsest grit possible and set any nails that may be in the way. Otherwise you will wasting many sanding disks.  We suggest visiting the links shown below for more information about flat subfloors and how to correct them.

Screeding low areas	Sanding high spots