Flooring and Carpeting Subfloor preparation for Marble Tiles, cement backer, hardibacker board

Flooring and Carpeting Subfloor preparation for Marble Tiles, cement backer, hardibacker board

Flooring and Carpeting /Subfloor preparation for Marble Tiles



QUESTION: Hello, I’m re-finishing my bathroom and I have removed the old 4×4 ceremic tiles and the 5/8″ plywood layer on which they were set. I now have a 3/4″ plywood subfloor and I was wondering what I should do. My choices are:

1) Apply thinset and 1/2″ thick hardibacker board. Screw it in. Install thinset and the 12×12 Marble tiles.

2) Install another layer of plywood 1/2″ thick? over thinset to make sure there is no air pockets? And then add another layer of thinset and then 1/4″ thich hardibacker board, screw it in. Install marble tiles has on a another layer of thinset.

What would be your recommendation. I have seen both wonderboard and hardibacker at Home Depot, and the Hardibacker seems easier to work with. I am also tiling the shower and was wondering if I need to put a moisture barier (ruber sheet) before putting the hardibacker.

Thank You

ANSWER: Thank you for your question Tristan,

Well to be honest with you Tristan I am not a fan of Hardybacker board. While the «Wonderboard» and «Durock» are true cement backer boards they do require extra effort to handle the stuff. My personal favorite is to use «Denshield» backer board. It’s made by Georgia Pacific and is priced pretty much the same as all the others are. The material is lightweight and has a fiberglass batt back to it so a vapor barrier is not necessary when hanging this product. It is also approved to use as a subfloor material. The material cuts like drywall but is a high performance wallboard that has Silicone additives mixed right into the gypsum compound that makes up the internal support structure of the board. That means that water will not «wick» or transfer through the material as it also has a «vinyl» face layer that is water proof. I have used this product in both floor and wall applications. Use this with a construction adhesive like PL-400 and screws long enough to reach the down into the floor joists not just the plywood ok? The Denshield can be cut using a straight edge and a razor knife, very easy and can be shaped or profiled using a drywall «rasp» that you can get for about $8.00. It makes everything fit together better. This product is also found @ Home Depot but it will be found in the «drywall section» not in the flooring section ok? I do not know why. Once the Denshield is installed you will have an extra 1/8″ of elevation to use a larger size notch trowel when installing the 12×12 Marble. I use a 1/2″x 1/2″ square notch for all Stone installs. Now Tristan be sure to flat skim completely the back side of each and every piece of Marble with thinset, (use a white thinset) so that moisture marks or comb moisture marks won’t show through when everything is set. Ok Tristan, I hope this helps you with your project, feel free to return anytime you need to.

Perry V.

Flooring and Carpeting Subfloor preparation for Marble Tiles, cement backer, hardibacker board

QUESTION: Thanks for the answer. Could you tell me if I need to add another layer of plywood before putting down the Denshield. Or is the base 3/4″ plywood subfloor enough.

Also, with regard to tiling the shower, do you know if I need to put cement board over the shower tub lib so it covers it, or do I rest it on the top of it (ie not overlapping it).


Hey Tristan,

In the tile Industry the minimum standard for sub-floor structure assembly is 1 1/4″ thickness so with the 3/4″ layer and 1/2″ layer you are within tolerances and as I mentioned earlier the 1/8″ difference will allow you to have more control of how your new floor will lay. So just the two layers will be just fine. one thing I would add to when you are installing the Denshield is to use a degree of care when running the screws down into the floor joists, you only want to set the screws to a «flush» depth and not break through the layer of vinyl facing ok? Just snug it up so that a positive depression is met. If you run one completely through the facing never fear just run another about an 1″ away. understand? Now Tristan your second question is a good one and a frequent place where homeowners get tripped up during the board installation. Very seldom are the walls properly framed and with the advent of drywall and more recently the «pre-cast» cement boards popular today while covering the walls with these materials while easier have this little problem when it comes to the tub lip. In the early days we mudd float all the walls/floors so that they were perfectly plumb and or level. not many builders are willing to do it the «old fashioned way» so using these ready made wall boards if you don’t have great framing when the board is installed resting on the tub it typically will «kick out» the board and when you put tile over that the tile kicks out as well to match. not good, to eliminate this problem just let the board come to rest on top of the tub lip being careful not to let it drop down on either corner in front of one side or the other and this will make for the best possible option. It’s not a good thing anyway to allow any of the boards to come in contact with the tub deck because should water get through the joint it will «wick» right up the wall and transfer moisture to the framing if no moisture barrier is used ok? With the size tile you are using it will easily span the space and remember to use a Silicone caulk at that joint along the tub and in the corners from the tub to the ceiling. Thats it Tristan, take your time and drop in anytime.

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