Designing Kitchens and Bathrooms - prepping tub/shower walls for tile

We're preparing to tile our shower/tub surround. I'll be removing existing cultured marble wall panels and removing the existing lathboard/plaster walls to a height of 5 feet above the tub flange. The plaster walls are about 3/4 inch or slightly more in thickness.

I want to set the cement board at a height so that the last course of tile goes over the edge of the cement board/plaster joint above. Any drawbacks and pitfalls to sandwiching a sheet of 1/2 inch cement board on top of 1/4 inch cement board? I'll use the 1 5/8 inch screws for adequate penetration. Would you tack the 1/4 inch cement board to the studs with a screw in each corner and the lay the 1/2 inch on top and run the screws every 8 inches through the two sheets? One alternative would be 1/4 inch lath strips on the stud faces but at 64 cents a running foot, it would be cheaper to just use 1/4 inch cement board under the 1/2 inch cement board and I am sure it would be stiffer as well.

To achieve a height I need to match the cement board to the plaster in the vertical plane I may need to shim another 1/16 or 1/8 inch at the stud facings. I haven't seen wood lattice that thin so I may be forced to resort to cardboard drywall shims for that purpose.

All suggestions and observations are welcomed. Thanks in advance.

You can double up as you wish, but I would prefer shimming. One thing however, are you installing a plastic vapor barrier against the studs? It is highly recommended you do so to prevent moisture from getting in your walls.

Be sure to tape and mud (thinset) your board seams.

i have to ask.

why would you only go up 5' ? why not just remove it all the way to the ceiling ? that way, there would be no thickness issues.

condo...
Just an opinion...they probably just want the tile to about the top of the shower doors, and you can't get a good paint finish on cement board w/o a lot of work. Plus the way they want, no trying to retape corners. Oh, and cement board is commonly available only in 5' sheets IIRC.
Just my thoughts.

Material cost and labor. You really only need cbu from the shower head to the pan seeing the walls above this will not see much water.

Thanks for the input. I will definetly apply a vapor barrier to the stud faces, is 6ml plastic or building paper a better choice?

I was leaning toward layering the cement board to make the 3/4 inch deficit over using furring strips because cement board is cheap and the added stiffness might be a plus. Using furring materal would be simpler and more fool proof though.

The only reason I wanted to avoid going to the ceiling with the new cement board is that then I would be faced with finishing off three very visible joints where the plaster ceiling meets the tile and no way to conceal the junction by overlapping the tile a few inches.

Plastic or tar paper, it don't matter. You should be good to go, just remember to drap the barrier over the tub flange first, then trim it when the board is up.

thanx guys. learn something new each day.

I would have went with furring as well. Furring will be so much easier, why cut all that cement board if you do not have to? Furring will go up very quickly and 1/2 will be strong enough for any residential job.

Regardless of which way you go just remember to cement and tape all of your seams. I have seen disasters where guys skipped this step and tried to cut corners.

1/2" cement board over 1/4" cement board won't make the wall any stiffer, all it will do is add more weight than is necessary. Use firring strips, it'll be a lot less work and a lot less weight.:)

Very interesting discussion, you make me think. So I did some internet research and googled up a few facts of interest.

From James Hardie Backerboard (http://www.hardiebacker.com:) 1/4" Hardibacker weighs in at 1.9 pounds per square foot (psf) and 1/2" at 2.6 psf for a total of 4.5 psf in my application

From USG.com - Manufacturers of building materials for construction and remodeling, including SHEETROCK brand gypsum products, drywall, and ceiling systems - USG Corporation (http://www.usg.com:) 1/4" drywall registers 1.2 psf and 1/2" is 1.7 psf. So for comparison, 3/4 inch of drywall would load the wall at 2.9 psf.

Now as for the rock lath and plaster I'm removing, while I couldn't find a reference for weight, I can assure you it exceeds 3/4" of Hardibacker or drywall by a wide margin. For example, according to USG again, a square foot of applied 3-coat stucco of 7/8 inch thickness weighs an amazing 13.7 psf, if the lath and plaster doesn't weigh at least 7 psf I'll be amazed. Additionally, the long wall in my tub surround is composed of 2x6 studs, with no covering on the back side. Factor in the 3/8" cultured marble panels I'll be replacing with porclain tile (even running the tile an additional 3 feet up the wall) and I'll have plenty of unutilized load capacity.

As for 3/4 inches of Hardibacker not having a strength advantage over 1/2 inch, how could that be? Isn't a 6 inch concrete slab stronger than a 4 inch? Isn't a 2x6 able to carry a greater load than a 4x4?

Don't take this the wrong way. I'm learning and thought others might be interested.

Geez, I forgot, USG lists Durock 1/2" cement board at approx. 3 psf which they describe as "one fourth the weight of a conventional 1" thick metal lath and portland cement plaster system"----or 12 psi. So while I'm extrapolating a little, I'm guesstimating my 3/4 inch rock lath and plaster might come in at 9 psi, or twice the weight of the materials I'll be replacing it with.

Foot

My point is simply this. You don't need to add that weight to the wall. The 1/4" wood strips will be lighter and easier to work with. Cement board is a pia to cut and work with. Additionally, 1/2" is rated for walls and all you will need.

I'm not saying that the 1/2" over 1/4" won't work, just that its heavier and a lot more work than you need to do.:)

Good to see that this stimulated some research on your part though.:D

HeresJohnny,

I do get your point and I'm sure you're right. Thanks for making me think hard, that's always a good exercise.

At this point, seeing as how I've already bought the material, I'll probably just double up the 1/4 and 1/2 rather than lugging it back to Home Depot and hunting for some suitable furring material. At 64 cents a running foot the 1/4 inch pine lath wouldn't have been much cheaper than the extra cement board. Being as how I'm an amateur I often do things the hard way:)

HersJohnny, HotinOKC, onlinehandyman, et. al,

I won't be getting started on the surround until the 15th of this month.

What are good options for furring material? I've used lattice strips and cardboard drywall shims on other applications. Would asphalt shingles or vinyl peel and stick tiles cut into 1.5 inch strips work? What do you suggest? Also, do I need to run the furring material the full length of the studs or just be sure it backs up the screw locations?

Thanks for sharing you expertise. Happy 4th!

Got another issue......

I cut out peepholes in the wall behind the long side of the shower and in the wet wall. On the long shower side and on the side opposite the wet wall, the studs are flush with the tub flange. On the wet wall they are set back 3/4 inch from the flange.

My assumption is that since I plan on replacing the plaster all the way to the ceiling, once I've verified the studs are plumb and level, I can use the 1/2 inch (really 7/16, I've learned) Hardibacker on the 2 walls with flush studs. That leaves the wet wall to be shimmed. It looks to me as though the existing plaster is 1 inch in thickness which spans the 3/4 inch gap from stud to flange andanother 1/4 inch to extend past the tug flange. If I duplicate that layout, would that be satisfactory? If I want to make my 1 inch thickness by sistering the studs to 9/16 before screwing on the 7/16 cbu, are there any pitfalls I should be aware of? I would need to notch one stud for an electric cable and possibly one or two for the plumbing lines, although I haven't seen how they are routed yet.

Thanks in advance.

Maybe what I need to do is nail up 1x2's on the face of the wet wall studs, bringing it flush to the flange and then screw on my 1/2" Hardibacker, leaving that wall 7/16" proud. I'm thinking I can then trim out the sides with bullnose to cover the sides of the elevation, I don't know the term for that kind of tile. This would also simplify my challenge of making the cbu flush with the adjoining plaster outside the wet area.

If the 1 by strips are a good option, would you nail or screw them? How far apart and how deep? I already have the 1 5/8" Hardibacker screws so they will still go all the way to the studs.

It is perfectly fine to sister studs to bring them in line with the rest. I would use a typical 2x4 stud to do this.

My assumption is that, once I've verified the studs are plumb and level, I can use 1/2 inch (really 7/16, I've learned) Hardibacker on the 2 walls with flush studs. That leaves the wet wall to be shimmed out. My working plan is to nail up 1x2's on the face of the plumbed wall studs, bringing it flush to the flange and then screw on my 1/2" Hardibacker, leaving that wall 7/16" proud. I'm thinking when I set the tile I can then trim out the sides with radius bullnose to cover the sides of the elevation. Anyone see any pitfalls with this?

If the 1 by strips are a good option, would you nail or screw them? How far apart and how deep?

Thanks in advance for sharing your know-how.

On second thought, why not install 1x3's or 1x4's horizontally on say 16 inch centers to fir out the wall before putting up the cement board? Am I on the right track? Should I also sister a few studs to the height of the flange to stabilize the tub? As I said earlier, until I strip the walls to the studs, I won't know for sure what I'm up against.

Don't forget to raise your comode collar if your doing the floor.
I did and not my comode is it high. Hope addding a wax ring solves it

A followup question, if you don't mind.

On one wall (the plumbed wall) the cement backer board will be 1/2 inch proud. On the outer edge where it will meet the existing plaster, I'm thinking I'll overlap the plaster by an inch and either caulk the edge with silicone or lay a shallow bed of silicone/with adhesive under the edge. I'm assuming that laying thinset and adhering the two dissimilar materials would be a mistake in the long run due to different expansion rates.

I do have doubled studs at that junction and so the cement backer and plaster would be screwed into seperate studs.

Seem like a good plan?

Different expansion rates? I think one could almost get a head ache from trying to over-think everything, trying to outsmart every possible scenario. It's about at that time that something else comes up and bites you.

On the recent one I did, I too had the finished wall about 1/2 inch proud, as you say. And at the vertical plumb edge at the entry edge of the tub, and along the top, I trimmed it out with 'outside corner' trim, with silicone caulk imbedded under it. And on the outside of it, I used paintable acrylic -siliconized-latex caulk at the joint. And since I used glassboard on the head wall, butted in the inside coirner up against existing long wall plastic, I used inside corner trim imbedded in silicone caulk there.

Whenver I have used an adhesive and silicone caulk to accomplish adhesion and sealing, I have used the adhesive to way within an inch of a seam, then imbedded under the seam itself with silicone caulk under the belief that gives the best absolute water-proof protection, in case water were to 'work on' that joint.