I was given an article from the pages of Fine Homebuilding magazine entitled Installing a Leakproof Shower Pan. I enjoyed the article. It seemed very thorough. But in it it stated that unless the bottom course of backer board was installed 1-1/2 in. from the pan floor, moisture would wick up the board and create a variety of problems. I have 2 questions: 1) What are some examples of problems that could occur if the backer board were installed too low? and #2)When the author states 1- 1/2 in. from the pan floor, does that mean under the mud? In other words, is the measurement taken from atop the vinyle pan? Is there any backer board behind the mud floor?
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story

There are lots of ways to minimize air leakage and improve energy efficiency, even in an older home.
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Suz,
You will get much more informed answers over on Breaktime, which corresponds to the Fine Homebuilding magazine. There is also this site:
http://johnbridge.com/vbulletin/index.php
which is devoted to tile and may have already answered your question. If not, ask it there and get advice from experts.
I found nothing on that website. But I posted my question anyway. ANYBODY out there who has experienced any problems from wicking backer board in a shower? I need to hear from you.
You might also ask at Breaktime. (Click on the Breaktime button in the second row of buttons near the top of the window.) People there will also tell you to ask at John Bridge if you don't mention that you already have.
You might also search the Breaktime archives. I'm fairly sure I've seen discussions there about wicking backer board. Click on the Advance Search button near the top of the index frame, the one on the left that shows the list of threads. I would first try a search for wicking and shower or wicking and backer.
The main reason you've only gotten one response here is that this forum is aimed at discussions of design as in esthetics rather than design as in engineering and choice of materials. We're happy you're here, but for this question, it's kind of like asking barbecue questions at the ice cream store. :)
I built a shower pan in accordance with the article. It worked great. The backerboard is 1 1/2" above the subfloor. In my case, I added another 3/4" floor over the original subfloor to give a sturdier platform for the shower.
You may have noticed that a slope is placed on the subfloor with a mud mixture and then a liner is installed. This liner is fastened to the studs above the highest possible water level. There is also a 2X10 blocking area around the rim of the shower between the studs to support the liner. The backer board is placed over the liner, but well above the lowest part of the liner. Once the actual pan is formed with mud on top of the liner, it will join with the backer board at the higher level. If you think of the 2-3" thick pan as being relatively impervious to water, you can still imagine a leak in the grout at the bottom of the wall or around the drain. This potential result of a small leak over time will allow the water to migrate to the liner. If the backerboard is well above the water which may collect in the pan, it is less likely to wick up and over time destroy your framework, assuming you have installed the pan correctly with the weep holes uncovered.
One thing that the article failed to mention is that you will need a sealant from the noble company, as well as the liner. Go to their web site. You will find the sealant there and you can buy from them over the internet. DO NOT use any other sealant with the Chloraloy membrane.
Good luck. If you post a reply, I will probably not see it as I don't usually come to this forum. E-mail me if you have further questions.Les Barrett Quality Construction