View Full Version : Evidence of moisture through the back of backer board

04-25-2011, 06:09 PM
Hello... a few years ago as a novice shower builder I remodeled a bathroom in our basement meticulously building a custom base with the appropriate multitiered drain assembly, rubber liner, and respective layers of poured concrete. I then installed a backer-board (recommended by an employee at Menard's) which was not true cement board but advertised as being excellent for tile showers and much lighter weight than traditional cement board. I had the tile professionally installed and it turned out great! After the grout was completely dry I applied two layers of tile/grout sealer. My son moved home about 18 months ago and since has been using that shower daily. Now I am turning my attention to remodeling the rest of the basement. In doing so I pulled off the sheetrock on the back side of that shower and was surprised to see that water had penetrated the backer board and left stains and some mold in the lower quarter of the shower. Ironically where my rubber membrane runs uo part of the wall at the bottom of the shower there is no mold behind it(?). At any rate, the mold cleaned up fine and the backer board has not lost any integrity (still very solid). My first reaction was that I needed to replace the entire shower. Now after cleaning up the mold and validating the integrity of the backer board I'm wondering if it is just my neglect in not routinely sealing the tile that caused this. There is no sign of mold at all inside the shower and all of the tile seems secure and looks as good as new. Do you think I'll be fine closing this wall back up and ensuring I routinely seal the inside of the shower? I thought about using some sort of sealer on the back as well since I have the wall opened up (like an oil-based water penetration paint of possibly even spray on pruning sealer). Does that make any sense at all or should this be left bare in hopes of getting some air circulation in there to keep it dried out? Sorry this got long but I wanted to explain the situation as best I can.

04-25-2011, 07:14 PM
Cement board and hardibacker are not damaged by water, and resistant to mold, but they are NOT in and of themselves waterPROOF. Either should have a moisture barrier ( 6 mil poly or 15 # felt) installed under them

04-26-2011, 08:51 AM
Yes, thanks Jimbo. I've learned that (poly/felt backer) since I did this project. My question now is can I salvage the existing shower by sealing the back of it with something like "Drylok Oil Based Masonry Paint" or possibly even a spray on pruner/sealer which is also oil based and water proof. I would do this coupled with a stringent regiment of sealing the tiles and grout inside of the shower. Would that work?

04-27-2011, 04:30 PM
A sealer is not really going to help you much - the best way to do it is to re-do it.

Sealers do not make grout waterproof - this is a common misunderstanding.

I wish I had better news or could recommend a sealer that would do the job.

Good Luck.


04-27-2011, 07:57 PM
I assume this is backer board nailed to wood studs. No way now to isolate the wood contact, so that will be a problem.

04-27-2011, 09:46 PM
Might be easier to send the son packing..... :) Kidding

04-28-2011, 05:03 AM
Metal studs.
If you see a very clear + specific spot where water is getting into the wood, you could cut it out without damaging the shower (doing that requires tools and skills) and then put metal there. (non rusting).

even if you had metal studs, the H2O that came through would end up somewhere,
and could add to the eventual mold problem somewhere else.
So.... It's not a big fix.

04-28-2011, 06:50 AM
Might be easier to send the son packing..... :) Kidding

...and, then again, :) it might not be.

04-28-2011, 08:07 AM
He did leave all ready once before...


04-28-2011, 02:08 PM
Yeah... sending the son packing is definitely part of the fix! But as cookie said it would be cheaper just to build a new shower rather than pay the tuition. Interestingly enough I do have access to the back of one side of the corner shower. The other side wall has standard poly vapor barrier installed so I'm now thinking maybe I can get a VB between the studs and backerboard on the exposed wall to help correct that misfire. BUT... I now fear the PVC shower pan may be leaking so I am getting ever so close to demoing the whole thing and starting over!! (It's a shame because the bathroom itself looks GREAT.

Do it right or do it over I guess.

04-28-2011, 07:32 PM
It's paying for the food, LOL. I am the mother of 2 sons who know how much they can eat, and eat, and eat. :) With what I have paid for food, I could had built a wing to my house.

...and, if you think they are going to remember you when are old and decrepited think again, they got plans for your old age NOW...

They know where you are going! One day I ripped my tendon running, and needed help getting up from the sofa, so, I said, to young son who was helping me up, "what are you going to do when I am old, ugly, and derepited?" He said, mind you, without a moment's hestitation, " Finest nursing home mom, finest nursing home..." WHICH I said in retort, " the one you can afford eh?"

We had a good laugh, but secretly I am worried!

Fix the bath, :) Save yourself.