The problem with low expansion foam is that the foam has excellent adhesion to everything it touches. This eliminates the ability of the floor to "float".
Low expanding foam is also not intended to have any pressure applied to it, and over time the foam will be compressed. Then you will the same problem of having a low spot in the floor all over again.
Also the foam may not spread out evenly, or possibly create a high spot. If it doesn't spread out evenly, or creates a high spot, you will have to take up the floor to fix it.
This would probably work as a very temporary solution; but should be corrected as soon as time allows.
Spongy floor by: Anonymous
What about drilling a hole and spraying low expansion foam under the board? You can then fill the hole with a laminate repair kit in the same color as the board.
Spongy floor? by: Toby
If you have a floor that feels "spongy" in places it's most likely because the subfloor is uneven.
The only way to fix it, I'm sorry to say, is to take the floor back up and fill in the low spots with floor leveling compound.
The great thing about laminate is the fact that it clicks together without glue. Taking it apart is very easy, just remember to label all of the pieces as you take them out. This is to make sure they get replaced in the right order.
If you have any further questions feel free to ask.
