Are screws required with Hardibacker over a cement slab? I used just thinset and the panels are coming loose.

Question

I have a large room that was laid with Hardibacker under an engineered wood floor about six years ago. Over the years the hardibacker has come loose from the slab, due in part to moisture under the slab. The slab leak was recently corrected and now I need to put the floor back. Everything I read on Hardibacker says to use screws, but most of the time it is referring to a wood subfloor. No where can I find the specific instructions for Hardibacker used to level a cement slab.

Answer 1

Why would you need a concrete board over a concrete floor??  This is why you can't find anything about attaching it.

If there are problems in the concrete, just skim them out with floor patch. Then use standard methods for the floor covering to be used.

Hardibacker is used to make a wood floor more rigid so you can cover it with ceramic tile.  **JD

Answer 2

Seal the slab with an Epoxy sealer- if that was not already done. Then put down a membrane and a floating hardwood floor. When you s***w or nail through the water proofing you potentially create a leak again- other option is sleepers, and plywood-beyond that floor will always be at risk depending on the hydrostatic pressure from beneath the slab.

Answer 3

I agree with fireman 4.  Why put Hardiboard over a concrete slab?  You may want to contact the tech support line for Hardibacker about the moisture problem warping the wood floor.

Dave

Answer 4

Who ever laid the wood flooring to begin with should not have used hardibacker to prevent moisture from coming up from the slab. A sealer such as Bostik MVP should have been used to prevent moisture from seeping through the sub-floor. Once the sealer is laid, then the installation of the flooring can continue.

Edit:

If a moisture test was performed at the onset it may have discovered the moisture problem to start with. With that being said, the tile company should have grounded down any high spots in the flooring. They also should have never used the hardibacker as an underlayment. As you said the leveler should have been the way to go. The process for using it is somewhat simple. First make sure the slab is clean and free of debris, and nail a strip of wood across any door openings to keep the compound in the room. Secondly, apply a thin mixture of the compound with a brush, you may need to apply 2 coats. Finally after an hour between each coat, mix the self-leveling compound according to the instructions on the bag, and apply by pouring onto the floor, starting from one end of the room to another.

The Bostik MVP would be a great product to seal the floor once it is leveled.

Answer 5

there is no need for hardy backer on a slab floor you can patch and level with a latex under-layment  mix then I would seal the concrete foor with a good sealer, then continue with the flooring