Published on March 26th, 2018 | by Henri


Repairing and leveling old flooring

Q.  My wife and I bought a duplex in January.  It may have been built as storage for a greenhouse/florist, which would explain why it is built with a shed roof (single slope roof I’ve heard referred to as a “flounder house”).  The two units are upstairs/downstairs and about 500 sq. ft. each with a full basement.  Our upstairs tenant moved out in February and we had to have a contractor screw down the floor boards, as there were two layers of 3” planks on top of one another and set down parallel to one another.

Now the downstairs tenant has moved out and we need to replace the carpet, as they said it wasn’t new when they moved in 17 years ago!  When I took up a piece of carpet to see what was underneath I found an old foam pad and (Omalon system 350), and underneath that, something that looks like cement.  Our contractor speculated that it could be cement mixed with gypsum.  To me, it looks like maybe someone tried to smooth it out with plaster!

The reason I say that is that it’s white and when I knock on it, in places it has that hollow sound that plaster can have (which I don’t think is a good sign!).  Looking at the back of this floor from the basement, it looks like wood, so it seems that whatever this is was poured/added over wood.

Hopefully that gives you enough background information.  Here are a couple pictures so you can see the materials.

Subfloor pix

Reader-submitted photo

Reader-submitted photo

Reader-submitted photo

Now my questions.

First, the Omalon foam pad seems to have been glued down for about a foot around the edges of the room and at the seems.  It wasn’t until after I took up the pad with a plastic scraper that I thought about asbestos in the glue/mastic used to hold the foam down.  I know you can’t guarantee one way or another, but I just wondered if you might have an idea of what might have been used as an adhesive.  Or perhaps you’d recommend I find someone like an environmental engineer to come and check it out?

My other questions are about the subfloor.  As you can see from the attached pictures, it looks like cement and “plaster”.  I believe the trowel marks are from the glue for the carpet pad.  The cement is pitted in places, and in other (second picture) there is some crumbling.  The plan is to put down a pad and carpet, but I’m not sure how important it is for the surface to be smooth.  If so, should I scrape the loose stuff and fill with something?  The floor isn’t very level and I’m sure the pad will mitigate small divots.  Finally, in some places where the floor meets the wall, there is a gap.  I think that should be filled in, but I’m not sure with what.

Many thanks!

A. The whitish compound you see is a gypsum-based filler used to fill in the gaps between the wood boards you see from the basement and to level the surface before laying the pad and carpet. It needs to be scraped off, as it is not a sound material and it disintegrates easily as you have found out. It does not contain asbestos from what my flooring expert friend told me.

The adhesive used to glue the Omalon pad should come up with the removal of the leveling  material if, as I assume, it was applied over it. But if not, you can soften it with a hair dryer or heat gun and scrape it off with a broad-blade putty knife. If the hair dryer does not take care of the adhesive removal, you may want to try pouring boiling water on a small area at a time, scrape the softened adhesive and move to the next spot – a couple of square feet at a time.

But, with a wood base underneath, you would have to be very careful not to use too much water in order not to damage the wood subfloor and to wipe as much of it as you can as soon as the adhesive is scraped off.

It is probably best to avoid this method unless the wood base is as sturdy as the one you found on the second floor.

Once the adhesive and the leveling compound have been successfully removed, have a cement-based product such as Ardex or equivalent applied to level the floor surface and fill in the gaps on the perimeter.

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