I live in north Atlanta, GA. The boards behind the tile at my bathtub are wet and need replacement. The old construction used a green board on top of the drywall (both are wet and in bad condition).

I'm going to remove both and use only one level of boards.

Is it OK to use a green board with Redgard (as a water proofing membrane) instead of cement backer board?

What kind of Adhesive/cement should I use. At Lowes, they gave me MAPEI Type 1 to use but the Floor and Decor department told me not to use it as it will allow the tile drop after a while because of the water.

I'm not looking for a life time solution.

My reasons for using green board:

  1. Easier to use,to cut and handle for me.
  2. I already have the mesh drywall tape and the dry wall screws.
  3. cheaper.
  4. the James Hardi backer is 0.42" which will not level with drywall in the sides (0.5")


Your reasons for using green board are valid. They are along the same lines of reasons for not going to the gym and staying in shape.

  1. Driving to the gym takes time.
  2. I have more fun on the couch.
  3. I sweat and have to do more laundry.

These are lies we tell ourselves so that we feel better doing the wrong thing.

I understand that you don't want to take care of the issue correctly. I get it. You don't care about your shower, most don't. But it isn't about doing this perfectly, it is about how much time you are going to spend doing something wrong multiple times.

Put the green board up, coat it with redgard, stick on your tiles. The water will just wick to the other areas not covered in redgard or get behind the green board and leak somewhere else. You will be doing versions of the same thing over and over, you will have mold issues, tiles will fall off.

First there really is no difference between greenboard and drywall. They are basically the same material and both should not be used in wet areas. Your question infers that you are using green board (mold resistant) drywall as some sort logical precautionary material. When in fact it is just a marketing ploy.

The biggest issues that your tub surround has are - it has no moisture barrier and the tiles were not the right fit to go over drywall (you have to basically have to do a perfect job for this to last, grout has to be thin, and grout/tiles waterproof).

You are going to saving yourself a TON of time just ripping these out and starting over. I have a good answer on here that shows different tub wall installations. The one I would suggest for you is 1/4" drywall, plastic sheet, 1/4" hardieboard. It really is that easy and the thinner hardieboard is super easy to work with. You can do your demo and have your new wall up in about 3 hours. The tiles depends on the install method and type of tiles.

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  • Lol,Frankly I watched famouse youtube channel- home renivision DIY,he said this will last 20 years,I liked your idea,but may I know 1. Why using 1/4" drywall and 1/4" cement board (why not 1/2" from the ceiling to the shower area and then 1/2" cement board to the tub . 2. I didn't understand the plastic sheet thing,how to apply it. 3.if I used your way, would it be ok to put the drywall and then redgard, then the cement board and redgard again (instead of the plastic sheet) 4. Shall i use 1/4" regular drywall or green drywall..hope to get answers for my questions and thank you for your help – Chad May 22 at 22:14
  • The plastic sheething is just stapled on the drywall and is super easy to install - live 5 minutes, You can buy thick gauge plastic at any big box. Redgard is fine too - you will redgard the HB - drywall cannot be redgarded (read manufacturer instructions) and you do not want a redgard sandwich. The reason I suggest plastic to "newbies" is that it is pretty fool proof. You don't redgard right and water can get through (think corners and seams). But redgarding the outside is great and acceptable if done right - makes install time longer. – DMoore May 22 at 22:47
  • Also you can just use 1/2 HB but it is harder to install and harder to get flush - very stiff and can pull from studs. I have a really good answer on here with options - there is a ton of ways to install a tub surround. I just gave you perhaps the easiest. – DMoore May 22 at 22:49
  • The plastic sheet is very smart,you made it so easy for me,I have one more question,what cement to use over the seems and behind the tile (is the ready adhesive in the picture attached good) or to use the grey cement, the one you mix with water,please advise me a specific name to buy from Home depot or lowes,and just to know if I understood the steps correctly,I will remove the tile and work on the area behind it: 1. Screw into the stud a 1/4" green mold board 2. Staple a plastic sheet all over the area from the side of the tub to the other side 3. – Chad May 22 at 23:33
  • 3. Screw the James Hardie HardieBacker 1/4 in. Cement Backerboard(from homedepot) into the stud with backer on cement screws 4. Apply two coats of redgard on top of the HB 5. Apply cement on top of the redgarded HB and apply the tile 6.apply 100 waterproof silicon – Chad May 22 at 23:38

Do it right so you do not have to do it again.

I use Denshield for tiling bathroom surrounds. It is the same thickness as the drywall this means that there is no transition disparity between the drywall and the DenShield. ( assuming you have a single layer of 1/2" drywall in the rest of your bathroom ) It comes with a waterproof membrane already installed on it.

You use a fiber mesh tape and a liquid waterproof membrane, like red guard, over the seams, corner seams and also cover any of the screw heads with the waterproof membrane, the rest of the field is already waterproof and textured to except tile.

It is easier to use than cement board, you score it and snap just like drywall.

Place your transition from denshield to drywall so the final row of tile is over the transition joint ( meshed with membrane ) of the Denshield to drywall. This insures the last row of tile will cover the transition.

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  • Thanks for the reply Alaska man, travis have have a single layer of 1/2" drywall in the rest of my bathroom. I never heard of this product, I knew shluter-Kerdi boards but very expensive,I'm assuming densheild is something similar, I didnt find a place to sell near me, can you tell me please how much is the densheild board cost? Thanks for your help – Chad May 22 at 22:17

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