I’m about to start on a bath and I’m puzzled by something. All of the cement board I’m aware of comes in 3×5 ft (36 x 60 in) sheets. How in the world does one use this stuff efficiently in a world where 16″ centered studs are the standard? It makes no sense to me.
Thanks.
Ed
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Replies
what type of cement board?
Are you talking fiber cement board (as in Hardie) or concrete board units (as in Durock)?
Practicality?
I have no 'knowledge' on this topic, but I have wondered the same myself. Here are my guesses
First, the 16" stud spacing hasn't been standard for nearly as long as one might think. A closer look at pre-1960 homes will find studs spaced with far less precision than they are today. By an odd co-incidence, drywall as we know it didn't really become universal until about then.
Even in 1960, there was great controversy within the trades regarding drywall. As a result, the product is often installed by carpenters- rather than the plaster trades. Go figure.
This contrasts to tile, which was typically installed by an entirely different trade; tilesetters are associated with the masons- not the rockers. Tile is often applied to surfaces that are NOT framed walls. Who cares about stud spacing?
Most often, tile - and the backer board- are applied over another surface, rather than directly to framing. It's attached to the wall, not the studs. Apart from already being supported, one does not 'finish' the joints of tile board. No taping here! Instead, the entire surface is covered with thinset. Any difference between adjoining edges is resolved.
Another factor is weight. Why else is tile board not made in greater thicknesses? Even those 3x5 pieces are pretty darn heavy.
Finally, consider where tile is used. Baths and kitchens. Places where the wall has plenty of small openings for pipes. How large of a piece do you want to wrestle in those tight rooms?
I've never seen standard 1/2"
I've never seen standard 1/2" tile board placed over drywall (or plaster). It would seem to be foolish to do so, as the drywall would simply be a sponge for any leakage through the wall.
I suspect that the main reason the odd size has stuck around is that there's been very little motivation to change it. The total area you're covering is pretty small, in most cases, and is pretty chopped up to begin with, so you'd be making nearly as many cuts with some "even" size. Thus any time savings (the biggie for the tile guy) is minimal. And the manufacturer is obviously not motivated to save materials.
Cement backer board is available in various sizes, including 4x8 sheets. What is stocked at the local borg is another issue.
The 32x60 inch or 36x60 inch sheets just happen to be a convienient size for a standard 5 foot tub surround.
why use it at all?
IMO, catmanduex hit the nail on the head as far as the stock size rationalization. However, it's a moot point to discuss why or how it should be manufactured or stocked because in most tile setting scenarios it doesn't matter. I say this because while I've used CBU's quite regularly in the past, I see very limited applications to justify using it today. So the real question is why favor the use of CBU's as a tile backer to begin with? In the limited scenarios where CBU's might be favorable (over say drywall, Kerdiboard, or traditional mud set wall or floor substrate), I would stlll argue that fibercement is a better choice than CBU's..
CBU's vs. Fibercement
Both CBU's and Fibercement board are cement based products which will
wick water into their cores. Denshield is water proof and an excellent tile backer on vertical wet areas, and, it's much
easier to handle and cut than cement backers.
I use Schluter Kerdi for floor applications, especially in wet areas (baths,showers, entryways, mud rooms, etc.)
It's easy to install and provides protection against water intrusion to the subfloor.
just my 2 cents
Geoff
CBU? Fiber Cement? I'm Lost
I have no idea what "CBU" means .... though there are some places that I like to apply Cluster Bomb Units to.
Fiber cement board? Like Hardiboard siding? What has that to do with tiling a bathroom?
While Denshield is a fine product, it is not as water resistant as DuRock. According to the FHB article ("What's the difference?"), only DuRock is rated for continuous exposure to water.
Just because something is cement based it does not follow that it is porous. Doubt me? Fair enough .... now, go out and look at the local town's swimming pool. Sure looks like a cement product was used there (Shotcrete). Now, look at the stucco covering many houses; also a cement product.
CBU's...and other relevant info
CBU is an acronym for are Cementitious Backer Units. James Hardie makes fiber cement sheet goods as well as siding. That's what it has to do with underlayment for tile .
DensShield is acrylic coated drywall. Using it is the same concept as surface waterproofing. IMO, if you’re going for a surface waterproofing system, than Schluter System can’t be beat. I think the seams are treated more easily and reliably than Densesheild. It's also lighter and can give you an additional insulation value if used on an exterior wall. IMO, the perm rating is also one of the lowest available on the market and most consistently installed in the field.
Here an excerpt of Technical Data from the manufacturer, Georgia Pacific, that addresses the moisture resistance characteristics of DensShield:
“DensShield Tile Backer panels are mold-resistant, and have scored a 10, the highest level of erformance for mold resistance under the ASTM D3273 test method.When tested in conformance with ASTM E96, DensShield Tile Backer panels achieved a perm rating of less than 1.5 (42.9 ng/Pa•s•m2) alone, 1.0 (28.6) with dry set mortars. In a test by an independent testing laboratory, DensShield Tile Backer was subjected to a shower of water at 110° F (43.3° C), 12 minutes per hour, 24 hours a day, 7 days a week for six months. The installation had no grout between the tiles. No deterioration occurred to either the DensShield Tile Backer board, the framing members or the wall cavity.”
So DensShield is, technically speaking, on the cusp of being considered a moisture barrier. It’s not a bad material to choose in some situations, but I am not aware of any seam system for this material provided or specified by the manufacturer. I wouldn’t use it for shower walls. Any joint is very questionable in terms of being considered a moisture barrier. Kerdi, on the other hand, does qualify as a moisture barrier. All of its seam conditions are addressed by the manufacturer and are considered to be moisture barriers as well-- when properly installed: This technical bulletin excerpt is from the manufacturer, Schluter Systems:
“KERDI features a polyethylene core with a polypropylene fleece laminated to both sides. The material is physiologically safe and does not require special disposal. KERDI is 8-mil thick and has a water vapor permeance of 0.90 perms, when tested according to ASTM E96, using Procedure E at 90% relative humidity. KERDI-DS is 20-mil thick and features additives to produce a water vapor permeance of 0.18 perms.”