Mold resistant drywall for basement necessary?
Hello again;
As I move ahead with my basement finishing project, I’m estimating drywall needs. Is it preferable to use mold resistant drywall below grade? Is it only necessary in the area around the bathroom and walls against foundation (just in case)?
Planning to use non wood baseboard finish pieces.
I’m planning to get a good bathroom exhaust fan to be sure that we’re venting the bathroom well, as well as sealing around that room’s envelope as best we can to contain the higher humidity
We have a walkout basement to the north already drywalled by previous owner at construction in 2011-2012. The walkout portion is ~2/3 of the total wall length.
There is also a partial above grade section of the west wall that has been drywalled.
The basement is very dry, copious crushed stone under foundation and exterior perimeter drain.
Below grade walls have 2.5″ Thermax (west and south walls), with 1.5″ on a portion of the east to accommodate stair way. We’ve sealed around the Thermax edges and after much research we installed fir strips over the Thermax with tapcons into the foundation walls that will have drywall installed over it.
Mechanical room is located in NE corner.
Attached print of the basement. North is up.
I pretty much guarantee I’m missing something here.
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Replies
Hi Wayne.
I'm not sure why, but I don't see builders using much moisture-resistant drywall, even in areas where it may be beneficial like bathrooms, basements, and garages. In fact there are a number of different types of drywall for different purposes/areas of the house (impact-resistant, sound-reducing, etc.), yet all I see installed is standard paper-faced drywall. Not sure why, but probably inertia and cost, like many other things in the building industry.
Thx Brian. I watched one video of a contractor in Canada going through different ways to waterproof a shower for tiling and he indicated that code requirements are lax (in his opinion) for showers, and I'm wondering if that's one of the reasons as well. I'm freakin' overwhelmed by all the decisions we have to make, and information out there is spotty. GBA has been so worth the subscription!
In the past, I have used mold/moisture resistant drywall for bathrooms and regular drywall for other locations. This was what is called “standard weight” drywall. Since then, they have come out with “lightweight” drywall, and it seems to have completely replaced standard weight drywall because lightweight is lighter to handle and install.
But I do not want products that have been made lighter for convenience if they compromise performance in other areas. I have never used lightweight drywall, but research indicates there are downsides to the performance that are the cost of being lightweight.
No retailers in my location carry standard weight drywall, and apparently most manufacturers no longer produce it. So I drove 208 miles round trip to buy 6 sheets of standard weight. This also happens to be mold and moisture resistant drywall, which I did not need for this project, but it was the only type I could find that is standard weight. It happens to be made by Georgia Pacific, and is even slightly heavier than standard weight. It is also glass filled and is extremely durable, which allows for precision cutting and trimming for best fit.
So for all future drywall projects, I will use this brand of mold/moisture resistant drywall in all applications. Even if you don’t need mold and moisture resistant, I believe it is the best drywall for durability, sound deadening, and resistance of fasteners to fracture the sheet if studs twist after installation.
That “glass filled” drywall is probably their Densglass product. That stuff is rated for exterior use. You can use it inside too, but it is a little trickier to finish due to the rougher surface. I’m planning to use it in some troublesome skylight wells soon, and will just do a quick skim coat to get it ready for paint.
I use 5/8” for everything else. “Light weight” doesn’t compromise as much in the 5/8” stuff in my opinion, although it doesn’t seem to actually save all that much weight. All the 5/8” drywall I’ve seen has been fire rated, which I think limits how “light” they can make it before it can no longer stay together well enough to pass as fire rated.
Bill
> That “glass filled” drywall is probably their Densglass product.
There's also DensArmor (https://www.buildgp.com/product/densarmor-plus-interior-panels/) which is an interior version of DensGlass, and there are similar products (canonically known as paperless drywall) from other manufacturers.
I have some DensArmor in my basement and plan to install a bunch more. It's a nice product. The fiber face means that, depending on the finish level required, it might require a bit more work to get to a finished surface.
I'm a commercial architect in Atlanta and in one of our lunch and learns the rep from USG told us that all their GWB is now fire-rated. This is for manufacturing simplification. No need to produce two product lines. Makes sense.
> No retailers in my location carry standard weight drywall, and apparently most manufacturers no longer produce it.
What do you mean by retailer? If you're only dealing with big box (e.g. Home Depot/Lowes), it may be beneficial to talk to real building supply companies.
Hey Ron.
What are the downsides of lightweight drywall? Is it a durability issue?
Ron,
Lightweight drywall has been around for about a decade now, and apart from the initial skepticism that greets almost every new product, I've never heard a contractor or homeowner complain about it.
I expect that it's far more important that you use a dehumidifier to keep the drywall (and everything else) dry.
I don't know about basements, but I agree with that for spaces like bathrooms and kitchens. The surface of the drywall should already be protected by a good paint finish, and if the drywall regularly receives water, it shouldn't have been used there. Relying on mold-resistant drywall to deal with excessive humidity is sort of avoiding the problem.
I agree on all counts. As the one doing the work, and the one that'll deal with screw ups, I'm willing to spend some extra $$$ on better quality.
Luckily, we're starting from a good place with recent construction, a well built foundation with good drainage and decent site work. I'm having a hardscape contractor come check out shifting retaining walls around the foundation. The builder did kind of cheap out on this.
BTW, if tile/grout doesn't really shed water, how did it end up being used in areas where there's a boat load of water? Does it date back to Romans using it in their baths (or so I've been told)? Is it all aesthetics?
Wayne "Curious Homeowner and Recovering Engineer" Maceyka
Wayne,
Glazed tile sheds water, but historically all tiles were set on masonry substrates, so it really didn't matter that much how much water got by as long as it could dry fairly quickly. Setting tile on drywall is a very recent idea, and a bad one, except for areas where it is only there decoratively.
We unusually never use anything but cement board in lieu of drywall under tile in shower areas....hardibacker is one brand...we do use Kerdi Board also on occasion.
Green board in the basement area and cement board as Hugh suggest for the tiled shower area should suffice. Otherwise go with blueboard and plaster. The lime based plaster will be pretty much water proof and a bit more effective dealing with mold.
The drywall that I used is 1/2" TOUGHROCK MOLD-GUARD GYPSUM BOARD made by Georgia Pacific. It is light green color. I am not using it for moisture or mold resistance, but only because it is of the standard density rather than Lightweight. It has glass fiber in the core, but also has the paper on both sides. It is actually slightly heavier than standard weight.
When I said that standard weight drywall is not available at retailers in my area, I mean all retailers including five lumber yards. I found the type that I bought at Menards which is 105 miles away.