View Full Version : Do we set the tub and then put up wall?

03-05-2007, 09:49 PM
We are taking out the tub completely and going to install another. Do we need to put it on some type of mortar?

Also, do we put up whatever vapor barrier and wall before setting the tub or after? I am thinking after but want to make sure. Thanks!

Dunbar Plumbing
03-05-2007, 09:57 PM
Yes. Set it in a bed of mortar, sort of a slurry that is compressible when you set the tub.

Make sure it squeezes out good, have the bare studs marked level for the tub to know when you've gotten the tub down far enough.

Once that tub is set, stay away from it and don't disturb it for 24 hours.

The walls can wait for another day. Otherwise the mortar you set the tub in will start to slag and leave voids under the tub.

03-06-2007, 04:10 AM
After tub is set tight and hard, wall material goes up on studs.

What do you have planned? Tiled walls? If so, the backer material hangs over the tub's flange (the edge that you don't see when the walls are finished) without touching the tub. If wall material butts down onto the tub, water will soak into it whenever water gets there. That air space is necessary.


03-06-2007, 08:38 AM
Thanks for the info.

Yes, we are planning on using tiles. So no backer board is between the tub and studs? Good thing I asked.

What can we do for creaking floor boards in the bathroom? We're wanting to put tiles down also. I have read a little about Kerdi, is it a good thing for me to use as far as a vapor barrier?

03-06-2007, 11:38 AM
The tub goes snug against the studs, and then backerboard goes on the bare studs but doesn't touch the tub's inside. If you "fur" it out slightly, it can hang inside the tub, over the lip, but that is not absolutely necessary. Later, tiles get cemented onto this and they overlap enough to close the gap.

A sheet of plastic can be stapled to the studs first and that can hang down into the tub, since plastic is flexible it can wrap around the edge of the backboard. That is the original vapor barrier, the way it was done for years before more modern and more expensive alternatives were available. Kerdi is good too. Wedi is good too. This last one, Wedi, is both a backerboard and a vapor barrier all in one; made of hard foam with a fiberglass and cement coating; far far easier and faster to work with than any cement-based product like backerboard or Kerdi.

.... So no backer board is between the tub and studs? Good thing I asked.

What can we do for creaking floor boards in the bathroom? We're wanting to put tiles down also. ....

Do you mean tile the floor, not just the shower? You have to tell us a lot about the joists holding the subfloor up.


03-06-2007, 01:11 PM
You might want to take your questions over to the John Bridge Tile forum...


They're very DIY-friendly and the info is top-notch.

I assume this is a tub/shower combination, and so a vapor barrier of some kind is needed. You can read up on the different methods and requirements, including Kerdi, on John Bridge or just ask them.

Good luck!

03-06-2007, 01:35 PM
What can we do for creaking floor boards in the bathroom?

I believe one of the tile sites has a load calculator (but I cannot locate it at the moment), and you need to begin there to determine whether your floor system can bear the additional weight of a tiled surface. In my own case, I doubled my floor joists for strength and renailed my decking to both old and new joists before using concrete board to begin building the tile covering.

03-06-2007, 02:43 PM
Yes, you need to check the floor structure to see if it would support tile. Sounds like the floor is planks. If that is true, you need to buy some deck screws and re-anchor it well, then you'll need a minimum of 1/2" plywood (all sides C-rated or better, i.e., no D sides) attached to the planks. Then, you can put down cbu or a membrane (Ditra is one) and tile. The planks may have plenty of acutal strength, but they change size too much between seasons - you need the more stable plywood on top to provide that stability. There's a deflection calculator over on www.johnbridge.com (http://www.johnbridge.com). Use that to determine if the joists are okay for tile.

03-06-2007, 05:06 PM
the deflection is a slight sag, and THAT is what can put hairline cracks in your tiles. Deflection happens when people walk on the floor. To be precise about it, deflection is not because of the weight of the tile itself.


03-07-2007, 04:04 PM
We have linolieum on the bathroom floor which is a medium sized bathroom, about 7 1/2' x 7 1/2' and has 8' ceiling I believe.

The creaking drives us nuts at night. Before we put down tiles on the floor we would need to take care of the creaking but since the area with tiles won't be so big would the weight be an issue? There is a 54" vanity and a toilet then the tub which is Americast by A.S.

We need to use Ditra on the floor?

03-07-2007, 06:19 PM

What is a joist? Find out everything you can about the joists under this particular creaky floor.

Whatever sections of all the above posts you don't quite understand, discuss here. :)


03-07-2007, 09:09 PM
The size of the floor you are going to tile is nearly irrelevant, it is the support under it that determines how far it can deflect, and whether it is strong enough to survive without cracking things..

03-09-2007, 10:12 PM
Hello. If you are putting the tub against an exterior wall, make sure you insulate and vapor barrier before you install the tub including using acoustic sealer between the floor and the vapor barrier. After that, install your tub with your mortor and let it sit at least 24 hours as someone else suggested. When you do your walls, it's better to use a concrete board rather than drywall everywhere you want to tile. This is because the drywall may absorb some of the moisture from the dry-set mortor that you will be using for your tiles and leave you with a less than adequate bond. Bring the concrete board down to where it just touches the rim of the tub, but not on the metal edge that you use to fasten it to the wall. When you tile, fill the space with dry-set morter, which is water resistant, and tile right down to the tub except for a normal space for silicon. Some people like to use grout to finish right down to the tub but I prefer silicon for that last edge as it is flexable and with people getting in and out of the tub, water load, etc, some flexability is always a good idea. As far as the floor goes, you can use 1/2 inch to 5/8 inch plywood to stiffen things up, but again I'd prefer to use the concrete board and a product like Ditra because the plywood would tend to absorb moisture from your dry-set and weaken your tile bond.

03-10-2007, 11:20 AM
Thinset on ply, drywall, or cbu can all be done without problems. In fact, cbu can suck moisture out of the thinset giving you a poor bond worse than ply or drywall. Each has their place, and using the proper thinset and mixing it accordingly will produce a fine, long-lasting result.

Do NOT use drywall where it can regularly absorb moisture. It will NOT be damaged by the moisture in thinset during the install process, but will if it sits in moisture on a continual basis. This makes drywall unacceptable in a tub shower surround below the height of the showerhead (the area considered wet). Drywall in a dry area can have tile installed without problems.

Plywood can accept a highly modified thinset and produce an acceptable tiled surface, but most people don't do the prep right, and it often fails. It won't if you follow ALL of the steps EXACTLY. There is more leaway if you use cbu or a membrane on top of the plywood, so most people do it that way. Both methods are approved by the Tile Council of America (TCA) which is the basis of most local codes.

Except in locales where they haven't updated their code, greenboard is no longer acceptable. There are better products.

Bob NH
03-10-2007, 12:17 PM
Thanks for the info.
What can we do for creaking floor boards in the bathroom? We're wanting to put tiles down also. I have read a little about Kerdi, is it a good thing for me to use as far as a vapor barrier?

Creaking floor boards are not a satisfactory base for ceramic tile. You usually need a double layer of plywood. If it moves enough to creak, then it may not be stiff enough to support ceramic tile without moving and cracking the tile.

Smaller tiles will survive better than large ones.

Go to www.johnbridge.com (http://www.johnbridge.com) , read it a bit, and then ask some questions.

03-10-2007, 02:36 PM
mold grows on the paper.

Drywall has paper holding it together. Greenboard is the same; it is more rigid when wet, but it still grows ("harbors, fosters") mold.

Better drywall products may not turn out to be better, since their big new claim has yet to be tested. They claim to inhibit mold growth.

Hmm. I'll believe that in 30 years from now.


03-14-2007, 10:02 PM
I wonder why they used two layers of drywall? We were very lucky in that there is no moisture damage after all these years.

Will be checking those joists and reporting back. I looked on John Bridge's site but some of the explanations there are way over my head, sorry:( Thinking you all are going slow enough for me to understand so here I will stay for a bit.

03-15-2007, 09:15 AM
two layers of drywall? Well, 99.9% of builders don't care about giving you an inch more space to move around in; they have far more important concerns.

A second layer enabled them to fill space (volume) to get the wall positioning exactly as necessary. Another "advantage" that they could use to explain it to the customer who might happen to walk by as it was being built and ask about it, is that the wall sounds more solid when bumped into.

The cost of building materials is not the big factor. It's all in the measuring and cutting, time spent discussing and deciding where to place things (within an eighth of an inch) and time spent doing (and redoing), and then finishing and making it look good. Time spent on operations, not cost of materials.

I'm glad you are going to tile your bathroom, and do it yourself too. You decide how you optimize your space as you wish, and don't have to give in to a professional whose interest is in making every hour count enough that you won't complain later that you paid hundreds just for talk and no action. Construction oriented people don't feel comfortable charging for talk, not like architects or interior designers. My experience. From what I have seen.


03-20-2007, 11:38 AM
David, I was reading about Kerdi and wondering if we should use that in the shower area where we are tiling. My understanding is that you put this barrier up on the studs and then put Hardi backer board?

03-20-2007, 01:33 PM
it's an option. It goes on top of drywall.


03-20-2007, 04:15 PM
Kerdi has some unique properties. It is hygroscopic (water repelling) which keeps the seams from allowing water to penetrate, and you can attach it to a surface, and then tile directly to it. You use thinset on both sides. It requires that you also use their drain (it's slick) and the material on the floor, curb, and walls. Watch the video on www.schluter.com (http://www.schluter.com) and check it out yourself.

I did a shower over Christmas for my mother with it...neat stuff.

03-20-2007, 08:49 PM
But do I need Kerdi if there is something like Hardibacker board? Isn't Hardi similar to greenboard or durock? Are these any different?:confused:

03-20-2007, 08:52 PM
Another question. Do I use Ditra on plywood for the flooring once we figure out why the floor under out linolieum is so noisy?

03-21-2007, 06:29 AM
no and no.

Hardi, Durock and greenboard are all different in several ways.

If you use Hardi board, in a shower, the recommended installation is to put a plastic sheet between it and the studs. The plastic is then a "vapor barrier" preventing moisture from migrating into the studs, the wall cavity and the rest of the house. Many people have not had vapor barriers installed in their tub-shower, and have had no problems. The degree of risk is not determinable in advance. Construction methods cannot rely on indescribably perfect installation which also depends on a little dose of dumb luck to succeed. It is not a recommended practice to follow. Hardi looks and feels like it's waterproof, but it isn't. Check their web site. Hardi is not waterproof; it can let moisture migrate, it can hold water.

Why a vapor barrier? Nobody should ever rely on grout alone to block water, since grout is not waterproof itself (it can hold a lot of water) and it may be insufficiently applied in one or two places; although it can look continuous on the surface, it may cover big air spaces behind or between tiles that grab water and hold it. Pure water doesn't enable mold to grow, but soap and construction materials are food for mold. Once conditions are ripe for mold to grow, it can grow fast and give off mycotoxin gases and liquids, which might remain largely trapped behind the tiles. This explains why some showers "smell" and why powerful smells are released when showers get demolished. These mycotoxins are true excrement designed to eliminate molds' very own fecal matter; they are so powerful that they even act as chemical warfare among microorganisms, preventing other microorganisms from growing in their vicinity. That is how insulin was discovered, and that property is what makes insulin work for us. Most other molds give off excrement that hurts us; it weakens our immune system by forcing it to work very hard all the time.

The plastic sheet directs the flow of moisture down to the inside of the tub's tiling flange. This is good. Now, invisible water vapor has a direction to follow. Either it evaporates back out through the grout, or it slips down (percolates down) and collects into drips that go down into the tub or evaporate at that bottom edge where the collected water would have dripped off if it had been big enough to drop. Although a plastic sheet gets perforated when nailed to studs, this is not deemed to be a serious problem; people have not reported that studs have suffered at nail holes nor harboured mold there.

If you use Kerdi, the continuous layer of vaporproofing is now Kerdi, and not the plastic sheet. Kerdi needs support, so it goes on top of your wall surface, not underneath. Being waterproof, Kerdi ensures that the wall surface won't get wet; this explains why you can install Kerdi on top of any drywall. You don't need Hardi. You can still use Hardi, or Durock, but it is not required.

Squeaky floor:
you have a problem that Ditra may not fix. Squeaks are movement. Movement is bad. Study this first before choosing the under-tile membrane to use.


03-28-2007, 04:25 PM
Thanks David. I had two people come in to discuss my bathroom woes and I got conflicting advice and ways they would handle it. Are you surprised?:D

First one said Hari is not as good as Durock - he will only use Durock. Kerdi is not required with Durock use. As to the squeaking floors. He advised ripping out the flooring and check the joists, maybe even adding more support there then use some type of construction glue to put plywood down and then use cement board nailed down on the plywood. Sounds like a good idea?:confused:

Second guy said two sets of sheetrock, no barrier necessary if we use something he paints on, put some good nails down on the floor and squeaking will be gone:eek: I sent him packing:D

03-28-2007, 05:13 PM
There are paintable waterproofing systems, but they should be used on cbu. As to which cbu is better - that is mostly a user's preference. Each one has its advantages and its deficiencies. Some are not allowed outside where it can freeze. basically, as long as it is installed properly, it doesn't matter which one.

Until you know the joist structure (the part that holds up your floor), you won't know if it is stiff enough for any tile to survive. If the planks are in good shape, you would need to screw them down enough so that they are tight to the joists. If they are all dry and split, you might want to consider replacing them. You need four things for a tiled floor to survive: a strong enough joist structure, no loose or sqeaky subflooring, strong enough subfloor, and proper installation of all materials. As already noted, on a wood floor, you MUST have some plywood down since the planks (while maybe strong enough) move too much. Tile doesn't like movement, either vertical or horizontal.

03-28-2007, 05:56 PM
one more thing: according to the manufacturer, Kerdi goes on sheetrock (drywall), not on Durock cbu, not on Hardibacker cbu. Durock is not prescribed. :)


03-28-2007, 06:36 PM
You can put it on cbu, but it is harder, costs, more, and doesn't buy you anything! Now, if this is going to be a tub/shower (don't remember, didn't look), I'd consider it, since you never know about the bottom edges. They shouldn't get wet, but if anything did, that would be where problems would happen.