Need some advice. Second floor of an office bldg, lightweight concrete floor in most places, still in good condition. Renovating for a new tenant. Bldg about 25 yrs old. At some point, a tenant had up & down for a disco, with cutouts in the floor to look down on the dancers and also inside stairs. Cutouts are irregular shaped, about 8 ft square. When that folded, holes were filled in and it became a regular 2 floor office bldg. The carpet and tile are stripped and the botched repairs are visible. They used 3/4 ply to fill in the holes, and didn’t always end on a joist, resulting in springy areas. Sometimes didn’t shim well at all, resulting in as much as 1/2″ steps, which were floated with a white floor fill that is heavy and brittle. Half of the new space will be carpet, half will be vct.
First step will be to get all the plywood joints supported on joists. Don’t really want to pull up all the ply and shim it level. Owner has mentioned overlaying the entire vct area with Hardie-backer. If we do that, would it be proper to use floor fill to bridge the uneven areas, then square-notch trowel on some thinset to bed the Hardie (screwed down, of course)? Would another layer of 3/4 ply work as well?
Do it right, or do it twice.
Replies
Oookaaay! Looks like we have a unanimous opinion.
Let me re-state the question, a little more briefly. Would Hardiebacker work for an underlayment, with floor fill under that? Or should I just add a layer of ply?
Do it right, or do it twice.
HardiBacker makes an excellent underlayment material. I am not familiar with vct. The major advantages of HardiBacker (vs 3/4" plywood) are similar stiffness in a thinner layer (3/8" HardiBacker will approximate the stiffness of 3/4" plywood), and a greater moisture resistance (better for tile or other moisture porous coverings). HardiBacker is also less flexible and harder than plywood. It doesn't have structural characteristics as dependable as those found in plywood, by which I mean to say that I would not use it to create a structure where peoples lives depended upon its strength, it should be supported by other structure, whereas I have no such reservations about plywood. HardiBacker is much harder to cut than plywood, you can score and break it or cut with a diamond saw ... it makes a lotta dust. I hope this helps. I guess most everyone is watching the war.