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I am installing a mortar bed shower & need to know the details about using cement board for the walls. How is the joint between the cement board and the shower pan “finished”? How much space between board & pan?
Does board extend down into the mortar bed? Anyone know a good website that answers theses questions? Or have experience w/ this problem?
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"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.
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Ally,
1. vinyl shower pan liner.
2. cement board.
3. mortar bed.
4. tile walls.
5. tile floor.
2&3 can be reversed, so can 4&5, different people do it different ways. You don't need to do anything between the joint. Water moves into any concrete, that's why you use the vinyl liner, (attached to the proper drain assembly). If you really want to do it right, put some mortar down before the liner. Just enough to make the liner slope towards the drain.
*Ally, you should remove all those multiple posts too.
*A topic often discussed here. Search archives. As you ought to have before posting. (Why not check before AND after posting a question ... seven times?)
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Andrew,
I apologize about the multipe posts. It was my first visit to the site. When I noticed all of those posts of one single message, I thought, "What the hell happened!" As I was about 90 seconds into trying to figure out how to remove them, the kids started screaming about water in the basement. The water turned out not to be serious, but did require shutting off valves & a mopping operation.
I checked archives, but not thoroughly. I had installed the sloped mortar bed that morning (yesterday); I start back to classes soon, the bathroom is a mess; I hate using the tub, & I was getting impatient.
I assure you that as I have time, I will be a walking encyclopedia of the archives section. This is a wonderful site...wish I had visited it earlier...but then the computer has been down because lightning got the modem...then there was the car wreck June 26 that totalled my car.
And my ten-year old son's best friend was hit by a car...in ICU for three weeks...his funeral was Monday. Still, I am embarrassed by all those multiple posts...WAS NOT my intention to trash up the site.
Thanx for understanding & "NO, I did not make all of that stuff up."
I did receive an email from a person who referred me to another website which had precisely the PRECISE info that I needed.
Ally Dodds
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Gee, Ally, I don't know but your post reminds me of when Joliet Jake and Ellwood are cornered by Carrie Fisher in the tunnel and he starts in with, "IT'S NOT MY FAULT! I ran out of gas, the car had a flat tire, I got lost, there was a hurricane, a tornado, locusts..."
*I'd recommend holding the cement board off the mortar bed to minimize the possibility of moisture wicking up from the pan and into the board.Figure the top of your mortar bed, add on the proposed thickness of thinset and floor tile, and keep the bottom of the wall board above that. Realize that your wall tile can hang a bit below your wall cement backer board. When everything is tiled, seal the 1/8" to 1/4" gap between the floor tile and the wall tile with a backer rod and a high quality sealant.If you grout that joint instead of using a flexible caulk, the grout will most likely eventually crack and leak.There used to be a nice article on-line over at JLC...I'll see if the link is still viable.Here you go...Knowledge is good.
*Mongo,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
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Rich,
I "would" think that you & "glue boy" had been inhaling the same fumes, EXCEPT that I forgot to mention that "at the get-go" this was supposed to be a cosmetic job...i.e., a simple matter of pulling up the basic urine saturated bathroom carpet & replacing it w/ something more hygenic. That is "Chlorox-able".
As I uncovered layer upon layer of disintegrating "scum", I "discovered" the rot went down to the floor joists. I had not prepared a recent research paper on the intricacies of mortar bed showers, nor had I anticipated the need to do so. i.e., I was somewhat unprepared...other than my "archives" of FH, which go back to numero uno.
In other words, it was a case of "Oh F..., what do I do NOW?"
WHICH was WHY I turned to this website.
I sought good solid advice...& I received it, but NOT from you OR "glue boy"...
"Al" Dodds
& I don't need the spell checker.
*Mongo,Thanx for your info...Another reader had pointed me to the same article...only by e-mail. I am delighted that you put the link up so it will become part of "Archives" for other people who have the similar probs to link into.Also, you made a good point about the moisture wicking up the cement board...I was worrying about that...but I put a poly membrane behind the cement board & decided I had worried about the probs a heckuva' lot more than the previous installer had...And I plan to live here!Al Dodds
*I saw this, this week on "HOMETIME" discovery or TLC not sure. The cement board is a waterproof board that will not wick, the space between the board is grouted with a cement/mortar style grout. I think they ran the board into the pan.
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Now see hear, Al. I'm not about to feel guilty one bit because I posted something which you found to be not very helpful or in any way offensive. A thread very like this one regarding the very same questions was posted sometime in the past. So, please do check the archives again.
Too, that you turned to BT for your answers and got something more than what you sought is not too much skin off my nose. And that skin you're wearing, you best be looking for another because that one's getting kind of thin. As for me and "GlueBoy", we'll just continue to rattle along.
*Michael Byrne also has a forum for Q&A as well. You might want to post your questions there. The link is http://www.jlconline.com/forums/tile/
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Careful putting poly behind cementboard and tile. CB and tile together make a vapour barrier, so adding another is generally not reccomended by mfrs. due to the problems involved with trapping moisture between vb's. There's some stuff in the archives about this.
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How do you guys form your shower curbs? Tile backer screwed to wood framing? Metal lathe and mortar? In any case fasteners will be penetrating the shower pan. Aren't you worried about leaks there? Am I missing something?
David
*David, I think you are assuming backerboard would go on the curb and fasteners are how you hold it place. First, no penetrations in the pan membrane. Second, regardless of what some mfgs claim, some tpes of backerboard WILL wick moisture.To get around all this you simply float the curb with mud over expanded wire lath. The lath is fastened only at the outside and folded tight over the curb. Your mud base for the shower floor will help hold it all in place, although is should be solid on it's own. The float should extend up the walls a minimum 3" above the finished height of the curb.
*Thanks Rich for clarifying that. I'm guessing the mortar/lathe will be about 3/4" thick? So the backer board at wall/pan surfaces will have to be shimmed out to match.Setting the wall backerboard (almost) down to the shower floor and filling with backer rod and caulk might work, but I hate caulk. Mildew gets under it too easily. Bringing the mortar base up the walls, 3" above the curb sounds like the way to go.David
*David, the mud float can be flush with the backerboard. The metal lath is 1/4" T, so the mud float, including the key, is as thin as 1/2".I float everything in a wet area. If I were to use a backerboard on the walls, this is what I'd do:Backerboard screwed and glued to walls down to approx. 10" AFF. Pan membrane installed up to backerboard. Membrane nailed or stapled to walls min. 3" above curb. Nail off metal lath to walls, nails not below 3" above curb. Float walls flush to backerboard. Backerboard/ mud joint--as well as backerboard joints at corners--filled with foam backer and caulked with butyl. Tile as usual with thinset mortar as adhesive. Screws are coated concrete screws, mastic is backerboard adhesive. Nails are 1 3/4" hot dipped roofing nails.To me, this is way to much work compared with a full float on all walls, curb, and floor. Such a float will guarantee plumb and square walls. Square is important because when the floor tile is cut in against the walls, it's nice to not see a tapered cut floor along the walls. The thing about using backerboard is it will mirror whatever the wall is doing. Wavy or out of plumb walls will result in the tile installation showing these imperfections. The best way to eliminate this is to furr out the backerboard. Another way is to plane or furr the studs. This takes alot of guess work out of trying to furr just the right amount under the backerboard. A straight edge comes in real handy.Alot of work, but this is FINE HB.
*Rich,My walls are flat and square to each other and I already bought the Durock, so I'm going with the "hybrid" method. Next time I'll pluck up a little more courage and go the "full mortar". You're probably right about the extra work I've created. Once you start mixing mortar why stop...and the tools are simple.It's good to hear 1/2" floats are ok. I imagine a richer mix, like 3:1, would be in order?You said backer rod and caulk at the corners and at the mortar/board junction. Don't tell me you'd do the same with the tile? I'm thinking Durock filler and fiberglass tape at junctions and nothin' but grout in the tile.David
*David, what is the "hybrid" method? I wouldn't do with a 3:1 mix, it's too much material and will probably result in cracking because the cure is too hot. I use 5:1:1 (sand, common, lime) for walls and 4:1 dry pack(sand, common) for floors. Sand is #16 mesh or less and lime is Type S.Backer and caulk is for substrate only. Before grouting, I caulk inside corners, then grout over. This means the grout is not full joint depth, but the joint is nonetheless fully packed. Less cracking over time this way.You won't find it in the TCA Handbook, but the proper way to prepare the substrate for tiling is to isolate each wall, or panel, from one another. In mud, this means scoring the inside corner. With backerboard I take it to mean the corner joint is filled with a flexible joint compound. Is the Durock filler flexible?
*Rich,Mud base and curbs with cement board walls is what I called "hybrid".Thanks for pointing out the problem with a rich mortar mix. I'll do the floor and curbs with the 4:1 dry pack.By isolating each wall and providing a flexible boundary between walls, a controlled crack in the grout is encouraged. I'm not sure I'd like this in my shower. Forming a rigid shell within the building seems more appropriate. Since the tile and grout finished surface does not give without cracking, shouldn't the substrate be reinforced to prevent movement at crucial junctures. (In some cases this may be easier said than done.) Maybe roofing nails would be better than screws, since the framing might find relief from the substrate at that point.Rich, this is all theory for me, since this is only my second shower construction. I've never pulled apart failed installations to find out what doesn't work and hope I never have to. In any case I'm going for the "solid shell" approach, no caulk. Next time it will be all mud, no cement board, no caulk.David
*i By isolating each wall and providing a flexible boundary between i walls, a controlled crack in the grout is i encouraged. I'm not sure I'd like this in my shower. Forming a i rigid shell within the building seems more appropriate.David, what do you suppose would happen to a material like a portland based grout when subjected to strain which exceeds it's elasticity? If your supposition is correct, how would you fix this?The answer is the grout will relieve the strain through stress. This we see as cracking. Most notably, this cracking is seen at the intersection of two planes. (also seen at butt joints in single plane, but different subject) The solution is to substitute a material which has a greater elasticity. This is the easiest and most economical fix. Try as you may, you will not be able to add enough rigidity to overcome the expansion/contraction inherent in and of various building materials. All structures "breathe". This minute movement to and fro over time will cause fatigue in any material. Now add green wood, inadequate soil compaction, installer defects, or a host of other factors and see what happens to your rigid building. In fact, ask any bridge engineer or look at the Tacoma Narrows bridge catastrophe and you see the true answer is increased flexabilty. Ergo, caulk.Perform a test in your shower stall. One inside corner you proceed as you have described, one inside corner you caulk as I have described. You can even pick the corner nearest the exterior house wall to caulk. In due time, let us know the results.
*Rich,If the building moves enough, then the tile grout will crack whether there's solid bridging in the substrate corners or caulk. If the building moves very little then the solid bridging may be enough to keep the substrate and surface grout intact. In my first shower construction, I used the fibreglass tape and filler over all seams. That was a second floor shower. The framing had only shear strapping, no panels. That was six years ago. There's no cracking except at the ceiling/outside wall junction. This next shower is simpler in that there are only two walls, (both shear paneled and anchored to the foundation) and the pan with two curbs. Not the Tacoma Narrows. We'll see what happens.I really appreciate the discussion and advice.David
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I am installing a mortar bed shower & need to know the details about using cement board for the walls. How is the joint between the cement board and the shower pan "finished"? How much space between board & pan?
Does board extend down into the mortar bed? Anyone know a good website that answers theses questions? Or have experience w/ this problem?