A customer called wanting information on subfloor repair. When I arrived, he took me up the stairs to a bare floor. The other contractor he had hired scribbled some stuff on the floor, like “too high” with a circle or “low spot” with a circle, and I noticed a lot of scribblings on the floor. We went from the living room to the dining room, down the hall (which seemed to be the only flat spot of the house), to the three bedrooms. All throughout, there were notes on the subfloor. Through the tour of the hilly valley of a subfloor, he mentioned that the other contractor wanted to correct the issues with the use of concrete. I replied, “You mean floor leveling compound?” He replied, “They said concrete.” Even if the other contractor wanted to use floor leveling compound, I told the customer that this would not work for his plywood subfloor with all the issues he had. I explained how we would remove the plywood decking and cut back the high spots or sister up the floor joist to raise the low spots, and then glue and screw the plywood back down to make a flat subfloor. He liked the plan better than concrete and hired our company to do the work.
Our showroom floor was one of the most expansive subfloor jobs I’ve done. 2,700 sq. ft. of concrete needed to be shimmed every 12” to accommodate a floating subfloor. The shims ranged in thicknesses upwards of 21/8” at the lowest point. We didn’t want to pay
for that much self-level. It is now laser level and flat from one end of the room 71 feet across to the other side.
Another one is when we had a job to install a new 4” wide hickory floor. When we went to install it, we found out there was a 1/2” hump down the middle of the room. So, we pulled the plywood subfloor off and shaved the floor joists down to get us to a flat surface.
Finally, we have worked multiple jobs in older houses with a car deck subfloor. There are variances upwards of 1” across the floor. We find it easiest to place shims every 12” and lay new ¾” plywood on top. This gives us a solid, flat, and level base to work with, which leads to a nicer end-product. It is a trick I learned from Lenny Hall of Endurance Floor Company.
We had a lake house being remodeled to have an open concept. It had a mixture of pier and beam, and concrete slab construction from many remodels over the years. What a can of worms! When all the walls were removed, we had to remove existing tile, then pour up to ½” SLU in low areas and grind down ½”of concrete slab in high areas, while also building up the pier and beam areas with ¾” plywood to achieve one level surface for new wood flooring.