Soft Spot In Wood Floor On Concrete Slab


I have a soft spot in my new wood floor. It’s a real wood floor glued on cement slab. They are 3 inch planks. What should we do about it?



Dear John

If you have SOLID wood strips glued directly to the concrete slab, this sadly, is the type of installation that will give continuous problems over the years. I made that really clear in my “Wood Floor on Concrete” article. If this is so, this is just about the worst method for installing hardwood floors on concrete, and is difficult and dangerous to repair. I’ll get to this later.

What I am hoping is that you have a real wood laminated (also called engineered) hardwood floor. These are 3-5 plys of real hardwood, with the top ply being the finished and sometimes thick layer. These are the really great light duty floors (50 years of life) which you should find easy to repair. The soft spot was probably caused by a dip in the concrete subfloor, which the installer failed to fix before the wood floor installation.

Go to and find out who has their “Professional Wood Floor Repair Kit” in your area. If there is no dealer for DriTac where you live, you may need to convince DriTac to send you one by mail. Here’s what in it. The glue is a diluted version of the famous DriTac 6200, which stays tacky ALL it’s life (50 years and counting). This is really important in this sort of repair because for various reasons the wood might pop loose again if the wood expands (yes even laminated wood expands), and this glue will re-grab the wood when conditions normalize.

You will drill two holes in either side of the repair area (drill bits provided) and inject the glue (syringe provided) into one hole until you fill it, or see it come up the other hole. The void will be filled up now. Cut the dowel (also provided) and fit in each hole and cut it off with a fine flush cutting hand saw (not provided but available at Punch the dowel slightly below the surface, and fill with a colored latex wood filler. Clean up any excess filler and adhesive right away with a wet cloth and then a dry cloth.

This glue works well with most old adhesives, and because the adhesive is thin it meets it own level in the dip (don’t put weight on the repair or walk on it for a day), the soft spot is gone forever.

Now then, if you have a solid wood floor, you CANNOT use the DriTac easy solution. And I should say that gluing solid wood strip to concrete is a poor installation method indeed. But in this case you will need to remove some boards. This usually involves removing a series of boards that span across the dip. If the boards are short (short 1/2″ by 2 foot flat bottomed wood is used normally in this installation) you can simply split them in thirds and remove the middle section and the rest can be pried off the good glue. Clean all the adhesive off the concrete with a old chisel and Goof Off Adhesive remover. You will now have to fill the void or dip in the concrete with a non shrinking cement based mortar. There is a limit on the thickness of some of the floor leveling compounds so make sure you find a suitable one for the depth of this hole. Give the concrete patch a few days to dry.

Follow my free article for the list of removal tools. Installing new boards though is a bit tricky. Being random sizes the new wood (hopefully provided by the building contractor, the same stuff) means they will all have to be cut to size on at least one end. You will have to re-bevel all the cut ends to match your floor, and touch up these ends with some floor finish (water based usually looks best on prefinished). Follow the directions in the free article, about cutting, but no nailing here. Use a good urethane adhesive DriTac 7500 or Bostik’s Best and once all the pieces are cut to size (allowing for some bottom grooves to be removed on the last few pieces) “dry fit” the floor boards to make sure you can quickly and easily assemble them before the glue sets up. Read the glue can label to determine this “open time”. Be sure to follow the recommend trowel size, too thick a glue spread will never cure.

The last few rows that had to have their bottom grooves removed will need to be held in place with a heavy object overnight. What ever you do don’t get even a speck of this urethane adhesive on the face of the board. Be sure to order a can of special urethane glue remover, to get this stuff off your hands or while wet, on the wood face. Good luck, a tough job, but do-able.