Reader question: Hi there. I recently finished grouting my tile surround in my shower. I posted photos on Facebook and somebody questioned whether I had waterproofed the Hardiebacker 500 board. Much to my dismay, I had never even heard of this… Anyway, I went to the James Hardie website and see nothing about waterproofing being required… In my research, and reading forums, it seems quite evident that it is needed. .. I am not somebody that skimps out or cuts corners. I simply have never come across this… VERY FRUSTRATED!!! DAMN YOU HOME DEPOT 🙂
This is a common question. Furthermore, the last thing a contractor needs is for the whole Facebook community to be criticizing how a shower was constructed. However, after researching the manufacturer instructions for each backer board I find the confusion on the matter is understandable.
Is cement board waterproof?
This seems quite clear. Yet it seems like where the confusion comes in is when you look at the different backer board manufacturer’s instructions. Hence the question “Is cement board waterproof?” Well, here’s what some manufacturers have to say about waterproofing:
PermaBase (National Gypsum): PermaBase PLus is not a water barrier. Consult local building code for moisture barrier requirements.”
Wonderboard (Custom Building Products): “WonderBoard® Lite is not a waterproof barrier. If the area behind the backerboard must be kept dry, use RedGard® Waterproofing and Crack Prevention Membrane or Custom® 9240 Waterproofing and Anti-Fracture Membrane”
Durock (USG): “If waterproofing is desired, use USG Durock™ Tile Membrane or USG Durock™ Brand Waterproofing Membrane.”
Consult local building codes. Talk about passing the buck. Additionally, I believe that manufacturers are vague on purpose. Which cement board do you think will sell better: Brand A (waterproofing unnecessary) or Brand B (waterproofing definitely required)?
“If waterproofing is desired…”
Who builds a shower and doesn’t desire waterproofing? Furthermore, the problem is that most people that purchase the backer board from a big box retailer don’t have access to a TCNA Handbook. It sure seems like better instructions are necessary if more waterproof showers are to be achieved.
Now here’s where things get really dicey: if there’s a horizontal surface in a wet area it’s absolutely critical that it gets waterproofing put on it. Because if it doesn’t then failure isn’t just a possibility but rather nearly guaranteed. However, where is that in the cement board instructions?
Whereas a three wall tub surround could possibly survive with no waterproofing, a shower with a bench and a half wall is almost certainly doomed to failure. Certainly, this is no time to be vague on whether cement board is waterproof.