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Charly
08-15-2008, 12:03 PM
I have only recently heard about this and am confused about a couple of things. I am installing a fiberglass tub for a neighbor and when you look at the bottom it has a large piece of what I call Chip board (chips of wood glued and pressed together) and the legs are 4 x 4 wood. When I've stood in the tub, there is no flex whatsoever. I replaced the floor with 3/4" plywood and plan to lay vinyl linoleum.

1. Why would this be necessary?

2. With the majority of the wood not covered by fiberglass wouldn't it soak up moisture from the mortar, thus weakening it to some degree?

3. If it was absolutely necessary to support the bottom, even with the chip board wouldn't using a 4" or so wide board down the center of the tub be enough if anything was needed at all?

No instructions came with the tub or surround (both fiberglass) and not in any boxes either... Gawd I so enjoy remodeling mobile homes! NOT! lol

Master Plumber 101
08-15-2008, 12:13 PM
I just responded to this same question. Use a gypsom plaster, it's soft setting and the end result is great(my opinion). Why is it necessary? It gives the base a more firm setting,not necessarly to the bottom of the tub but at most the supports on the bottom of the tub.

lylec
08-15-2008, 12:20 PM
I will do something to help explain this for everyone, and for future reference. Since I have the side of my tub open, without any mortar bed, it is very easy to see the bottom flex when a person steps in it. I will take a few photos with a tape measure next to the bottom . I will take a photo of the empty tub, and then with a person it it. It is quite easy to see the entire bottom flex. The chipboard provides almost no strength. Go lay a piece of plywood 3/8"(which is stronger than chipboard) out on 2 2x4's spread 5' apart and then stand in the middle. I guarantee that the board will flex. I believe the chipboard is just for shipping/crate purposes, but it is not support for the tub bottom. According to my whirlpool specs, the weight with water is 554 pounds. Without the bottom fully supported, this weight is being held by the rim of the tub, which is not good.

Charly
08-15-2008, 12:38 PM
I can certainly understand with a 5' bottom needing major support, but this tub is only 27" wide, maybe a little less. I get nervous when it's suggested to use anything with moisture, no matter how little, when it's around wood is all. That's why I ask my questions and would prefer using wood if it was absolutely necessary to support the chip board underneath.

Granted I only weigh about 170lbs., but when standing in the tub and flexing my knees I feel no movement at all. I originally was going to put a strip of wood down the center for added support, as I know someone about 300lbs. will be using the shower. Then I heard about using a mortar or the like....

I've never dealt with gypsum plaster, but am presuming it is like what's in sheetrock. If that's the case, it doesn't break down at all over time nor would any moisture get into the chip board, floor or legs of tub?

Thanks!

toolaholic
08-15-2008, 12:57 PM
Charly, You came here because You don't know what Your doing. And that's why the pros help You. Now You 2nd guess the pros. I've been setting plastic in motar for many years without a problem. I first staple down chicken wire
to reinforce the motar. It keeps the motar from breaking up later.

Charly
08-15-2008, 02:30 PM
Charly, You came here because You don't know what Your doing. And that's why the pros help You. Now You 2nd guess the pros. I've been setting plastic in motar for many years without a problem. I first staple down chicken wire
to reinforce the motar. It keeps the motar from breaking up later.


My dad is a retired general contractor and I’ve been building houses and remodeling for over 30 yrs. Of all the tubs I’ve put in, I just never read instructions about using mortar, sand or anything else and this tub came without instructions.

I came here to gain knowledge and ask questions about something I’d never heard of doing on the information highway. No offense was meant or was second guessing implied nor rudeness expected… I cannot apologize for wanting to know all the whys, pros and cons of something I’m unfamiliar with for the good of the customer.

Guess I shouldn’t have come here to ask my questions…. It won’t happen again toolaholic.

Terry
08-15-2008, 03:20 PM
Charly,
Not all tubs need support.
If the tub is on the floor, not needed.

If it's stiff enough, not needed.

Sometimes mortar is used when there is flex.
Most deck mounted tubs need some sort of support.
Mortar, or something that sets up hard works.

I like the chicken wire idea. See, I learned something new today.
I've used steel mesh in driveways, so it makes sense.

I tried a time or two trying to get the exact level on the support below, and somehow got too much in.
I found that small piles or someone said ridges of mortar have worked, the tub squishes the mortar down to size, and there is space between the piles for it to spread, only as much as it needs.

leejosepho
08-15-2008, 03:32 PM
... when you look at the bottom it has a large piece of what I call Chip board (chips of wood glued and pressed together) and the legs are 4 x 4 wood ...


I originally was going to put a strip of wood down the center for added support, as I know someone about 300lbs. will be using the shower. Then I heard about using a mortar or the like....

I have a one-piece fibreglass shower/tub with a flat and solid piece of 3/4" plywood on the bottom, and neither could I feel it flex prior to installation. Nevertheless, I installed it with a tapered-to-fit 2X4 wooden frame (rectangular box) underneath it just to be sure some time ago, and now I can feel the bottom flex whenever I take a shower. I have easy access behind the tub and at its ends at the moment, so now I plan to add the mortar base I should have done in the first place. Foam failed me long ago, and now wood has done the same ... and that leaves us dependent upon mortar even if I do not completely understand why!

jadnashua
08-15-2008, 03:41 PM
Many older tubs were made of cast iron (and many still are). A CI tub is strong enough to not worry about flex, but even one of those can benefit from something under it if the floor is not both flat and level. No tub is designed to be completely supported by hanging from the rim. A few tubs have a structure that is fully supportive and works fine IF the floor is both flat and level. If your tub is not set level, you'll have problems with moisture running where you don't want it.

Any moisture used in mortar or plaster is chemically incorporated into the mix when it cures...there is NO water left. After that, the only way moisture gets under there is if something fails or you play water games in the bathroom. To help keep the wood dry while the stuff cures, a sheet of plastic works fine.

lylec
08-15-2008, 04:30 PM
To follow up Terry's point about how to best place mortar before setting the base, here are some thoughts. If you have ever set tile, you know that you use a notched trowel. The reason for the notches is to allow you to press the tiles down. If you try to press the tiles into a solid even spread of mortar/thinset/adhesive, there is no where for the excess to go. Same idea applies here, with several mounds or rows, or zig-zags, you can start high, and then as you press the tub down to the desired height, the mortar can spread. This is also why you do not put any weight on it for days, as there are voids that the partially cured mortar could still ooze, thus lowering the tub and removing the support.

Master Plumber 101
08-15-2008, 04:50 PM
If you never used gypsom plaster to set a tub(best used on whirlpools and shower bases) you should try,its the cat's you know what. cast iron tubs are probably not necessary to do so but works great with everything else. Try it once it work just as good as mortar and cets up nice and hard.::D

Terry
08-15-2008, 04:51 PM
and that leaves us dependent upon mortar even if I do not completely understand why!

And that is really the reason.
After time goes by, and you have cycle after cycle of people stepping in and out of the tub or shower, you start to break down the fiberglass and the wood.

yoyoma
08-15-2008, 09:05 PM
My plumber's assistant said he was not going to do a mortar bed when I asked him. Said it's not necessary since it's going to be supported by the 2x4s on the long side of the alcove. I checked the installation manual and nowhere did it mention mortar beds. So I called Maax up and they said it's "recommended" and they were going to update their manuals with this information. The guy at Maax also said if people using it are under 300 pounds then a mortar bed isn't really necessary.

I told the plumber's assistant to hold off on the tub installation. Then I called my GC and told him I wanted a mortar bed. Lucky I was there to see what they were doing. My GC said I shouldn't have to be there, and that it doesn't matter because you could tell the difference afterwards and make them do it over the right way with the mortar bed. He said to let them do it their way, don't watch them, and only later make them fix it. I thought it was better to catch them while doing it and save everyone time.

I also told my GC that I wanted the 2x4s on the ends too because that's what the manual states, and he said it's not necessary, just the long side, but if it'll make me happy then he'll do it. I fell bad pushing things but I'm the one who has to live with this, not them.

lylec
08-15-2008, 09:14 PM
This is on Page 2 of the installation instructions for the American Standard Plebe Whirlpool that is in my house, (incorrectly installed by the master plumber that installed it before I bought the house).

"This bath must be supported along its entire bottom in all types of installations. We recommend the use of mortar of plaster as bedding material (sand is not recommended). Apply enough bedding to support the complete bottom of the bath. After the bedding has been poured, and before it sets, lower the bath into place until the rim is leveled against the leveling stringers. The rim of the bath MUST NOT support weight. Allow the bedding material to completely harden before applying weight to the rim or bottom fo the bath. Any finish material such as tile or wall board must be self-supporting if it contacts the deck of the bath."

krow
08-15-2008, 10:04 PM
. I fell bad pushing things but I'm the one who has to live with this, not them. I always tell my clients

"At the end of the day, I get to go home, so you (the client), has to live with the end product."
I often ask if the client has a preference of how they would like a product installed because I don't want to be called back and be accused of not installing it how they want. Most of the time, the client will ask me to do it the "best way possible", so then I will install a mortar/cement pad under the acrylic tubs

yoyoma
08-15-2008, 11:48 PM
The question is how do I know the good plumber from the bad one? This plumber came on the recommendation of my GC so I used him. He's going to be back tomorrow to do the tub install and I won't be there unfortunately. I hope I'll be able to determine whether a mortar pad was installed even though I won't be able to see it. Based on today's experience, I don't trust them at all.

The plumber's assistant also installed a Toto Carlyle incorrectly. He flushed it, and it was making a trickling noise well after it stopped flushing. He was about to calk the base when I said, "What!? No way, fix it please". 10 minutes later he leveled it better and the trickling was gone. Now tell me why did I have to babysit them? I think a professional would get it right from the beginning instead of taking shortcuts hoping I don't notice.

Terry
08-16-2008, 10:01 AM
it was making a trickling noise well after it stopped flushing.


They do that when water is added to the bowl, or at the end of the flush. It takes a little while before the capillary action quits pulling the water down the trapway. It will stop fairly quickly though.

Your tub/shower faucet will drip for 35 to 40 minutes after taking a shower. I've had complaints on those too.

jadnashua
08-16-2008, 08:14 PM
NO tubs are designed to be held up by their rims on the ledgers...the ledgers are to hold the edges in case you sit on them and help hold things in place while the mortar bed sets up. The only tubs that don't need it are those with an engineered flat bottom that is already fully supported, or a cast iron one, and then, only if all of its feet are sitting evenly on the floor. Water weighs about 8#/gallon. Add say 30 gallons (and some can hold more than twice that much) and an average American and you've got easily over 400# hanging on that 1/4" thick lip of plastic...NOT a great idea. The tub WILL flex. They're fairly resilient, but in the process, it will stress the drain line and possibly squeak as it rubs against anything it touches.

I don't see the issue - this is not a corner to cut. Mortar is cheap AND it lets you get the tub perfectly level.

yoyoma
08-16-2008, 11:56 PM
The only tubs that don't need it are those with an engineered flat bottom that is already fully supported

Well, there is a plywood-type bottom plank underneath the bottom of the tub, but maybe that's just done for packaging. Not sure. I think this may be a misunderstanding because the plumber's assistant doesn't speak English well. It's times like these that I wish my GC used native English speaking subs.

leejosepho
08-17-2008, 05:50 AM
Well, there is a plywood-type bottom plank underneath the bottom of the tub, but maybe that's just done for packaging. Not sure.

Probably nobody knows for sure about that in every case, but my guess is that the old standards have been generally forgotten over time.

As far as I know, plastic showers and tubs first began appearing in mobile homes around 50 years ago or so while cast iron and steel were still being used in regular houses. At that time, a plywood bottom with short stilts to support the flexible tub probably seemed (or was deemed) solid enough to match the quality and expense of a trailer house ... and with maunufactured housing now confusing things even more, everybody has forgotten (or has never heard) about the great differences between a rigid cast-iron tub sitting on stubby legs and a flexible plastic tub sitting on short wooden stilts.

Overall, my guess is that the plywood bottom was originally there to simply hold the bottom of the tub in place (flat and sloping toward one end) until the mortar placed under it had set, and that the stubby legs were there so the tub could be pressed down onto the mortar without being pushed too far ... but I doubt that procedure was ever actually followed in very many mobile homes.

jw123
08-19-2008, 06:33 PM
I just installed a kohler acrylic tub that suggested two alternate methods of support. You can either use a mortar bed or put construction adhesive under the "feet" (2x4's on end). For the life of me I can't see where these two methods are comparable, but this is manufacturer's instructions. They also don't recommend any additional framing, i.e. a sill support, although they do suggest screwing through the tub flange into the studs. I can't see any flex when I stand in the tub and the weight of water doesn't concern me since it's evenly distributed over the bottom of the tub, but a point load like a heavy person could cause a problem. That said, it seems to be a strong design with interior armrests and contour that make it more rigid, so maybe this explains their confidence level.

William47
05-15-2009, 10:40 PM
tub has been installed. was going to foam under, but now want mortar. have access from end of tub. how is best way to add mortar after tub has been set into place permanently? this tub is installed perfectly level (right on the bubble all directions!) on a new level double 3/4" plywood floor and the install instructions said additional support was not necessary.

Don Gwinn
05-16-2009, 09:10 AM
Here's what I'm not getting, and maybe I'm overthinking things. I have a Sterling Ensemble tub, which is built with small round "feet" all over underneath. There are probably 15-20 of these small pillars built into the bottom of the tub. I'm well over 300 pounds and I know I want to use the mortar bed (though the instructions call this an "optional" method.) What I'm not sure about is whether I need to make piles around the feet while making sure the feet have no mortar under them. I wouldn't think that would be necessary, but there's that one line that mentions "directly on the subfloor."

On the other hand, it also says each part that would contact the subfloor should "have mortar." Never done this before and I want to do it right.


Install a Mortar Cement Bed (Optional)
Remove the bath and pad from the alcove.
Verify that the bath is level.

Shim if necessary.

Studs

NOTE: Do not use plaster, gypsum cement, or drywall compound for this application, as they will not provide adequate structural support.
NOTE: The bath supports must rest directly on the subfloor.
Spread a 2″ (5.1 cm) layer of mortar cement on the subfloor, spreading it so that each area of the bath that will contact the subfloor has mortar cement. Do not spread the mortar cement around the drain area. Allow room for the mortar cement to expand from the weight of the bath.
Immediately move the bath into position.
Verify that the bath is level and resting on all supports.
Clean the bath to reduce the risk of damaging the surface.
Place a clean drop cloth or other similar material into the bottom and over the
outside edge of the bath. Be careful not to scratch the surface of the unit.

Jetta Whirlpool Baths
05-16-2009, 02:28 PM
Sounds like Sterling wants those feet touching the subfloor. And have the 2" of space filled in with mortar as well for support.

When in doubt, do as the manufacture instructs.

I have had plumbers and installers physically get upset with me when I told them that sand, drywall mud and foam are unaccpetable bedding materials to set our tubs with. I get the usual angry responses of "I have been setting tubs for 20 years..."

The sad thing is a majority of manufacturers will void their structual warranties or sometimes the entire warranty of the tub because of no or improper support. :( not without good reason:

I have seen a plumber raise a whirlpool bath out of the deck 3 inches with foam.(too much)

I have seen someone put their foot thru a lasco tub/shower combo. (well the after effects)

And stress cracking on a Jacuzzi, that leaked from upstairs to downstairs and ruin $10,000 worth of an entertainment center below.

Just my $0.02

jadnashua
05-16-2009, 05:02 PM
Trying to put mortar underneath there now will be nearly impossible, at least and expect full coverage. Mortar (when allowed by the manufacturer) does two things: fully supports the bottom and compensates for any slightly uneven floor allowing you to get it level.

If the tub doesn't have an apron, you could do a good approximation of full coverage, but it will be tough.

Terry
05-16-2009, 05:14 PM
Allow room for the mortar cement to expand from the weight of the bath.



This is why I use piles of mortar.
When you drop the tub down, it will push the piles of mortar down, but it has to have somewhere to go.

If you try to go for a full spread, you are likely to either have too little, or too much.

Allowing the weight of the tub to do the spreading works best for me.

If the tub is in place, you can just push some in there.
It doesn't have to be under every bit.

Setting tile is the same way.
There is a notched spreader, and then the tile is pushed into it.

master plumber mark
05-16-2009, 06:56 PM
Here's what I'm not getting, and maybe I'm overthinking things. I have a Sterling Ensemble tub, which is built with small round "feet" all over underneath. There are probably 15-20 of these small pillars built into the bottom of the tub. I'm well over 300 pounds and I know I want to use the mortar bed (though the instructions call this an "optional" method.) What I'm not sure about is whether I need to make piles around the feet while making sure the feet have no mortar under them. I wouldn't think that would be necessary, but there's that one line that mentions "directly on the subfloor."

On the other hand, it also says each part that would contact the subfloor should "have mortar." Never done this before and I want to do it right.


Dont be intimated by this, its very easy..

in the last month I have had to installl 2 Sterling
48 inch shower bases.....and one whilrpool tub

I have found that a 60 lb bag of rather extra wet concrete (not soupy) works best spread out in a overall bed like fasion under the tub... you can figure where the edjes of the paltform are under the tub and end the bed as close to the end as possible...

when you set the base in the concrete it simply floats down to where is should be and the moarter fills in the gaps,
you might have to shake and shimmey the base to get it to set down, then you basically stand in the shower base and walk around getting the unit to sink in good...

I went back on one of them today and I was rather
impressed on how solid the bottom actually was....

it was like standing on a concrete floor with no give what-so - ever...


http://onsmartpages.com/weilhammerplumbingco/nss-folder/pictures/si_UEw80h80_april%2021%2009%20%20first%20communion %20097.jpg (http://onsmartpages.com/weilhammerplumbingco/pictures/view_alone.nhtml?profile=pictures&UID=10319)

Don Gwinn
05-17-2009, 08:13 AM
I'm going to try it on the piles. My concern was how to locate the piles so I wouldn't set any feet into them, but it sounds like these little pillars (maybe 3/8" across) will find their way down to the subfloor if one or two gets a little mortar underneath.

Thanks!

jadnashua
05-17-2009, 01:31 PM
Unless you mix the mortar up really stiff, the tub should settle into the stuff and don't worry about the feet - the whole thing will settle down if you help it out like Mark indicated. And, if the floor isn't perfectly level, you don't want the foot on the ground - you want mortar under it so it does sit even. Some people then fill the tub with water to help ensure it doesn't float until the mortar sets.

edwardh1
09-29-2009, 05:15 PM
2000 + people have read this topic. The word must not be getting out about what "mortar" to use-
lets see
-plastic on the floor
-plastic under the tub
- 1/2 to 2 in of space between the two plastics
- motor in piles
- but what exact brand mortar is best? something HD, lowes or a lumber yard carries?
- and what about bedding compound - what the heck is that if different from mortar

=========
Izzi tub people say on their web site to NOT USE CONCRETE as it shrinks, but to use wood shims
=========
MTI says that no concrete is needed if you have a foam base under the tub (this is an extra cost option)
=================
Jason says that mortar should be used if the floor is "not level"
+++++++++
None of them say anything about when you set the tub finally with no bedding compound, what the allowed gap betwen the finished deck and the underside of the tub rim is-
what should it be 1/8 inch or less??? I think toto says 1/8 inch
Then you caulk it????

==================

HoracioO
09-30-2009, 12:57 AM
I'm going to throw my 1.5 cents in... only from what I've observed...

I have 50 year house.. it has a fiberglass neo shower that I recently tore out. Original gear so Fiberglass shower bases have been used for at least that long. This one had a poured plaster (lime not gypsum) sub floor to tub support that did not crack and had no reinforcing—chicken or otherwise.
A shower drain set in poured tar like substance that had been poured hot... the shower drain was of course caulked to the pipe with poured hot lead & jute... this system worked for nearly fifty years and did not fail due to cracks.
The shower system failed because of the bad shower wall to plaster/shower glass surround transition; the shower wall's one seam also leaked and the killer issue was that the wall system was chip-board (trade name) covered in a formica like material rotted from sitting on the shower base lip and sponging up the water.
This house also had an outside bathroom with an old metal enamel shower base that was set on a a concrete floor with just straight dirt from outside in the garden... needless to say the bathroom was non functional as someone probably failed to winterize... but the base was there until I demo'd it

Now... a quote from the install instructions for a Sterling shower base...

Install a Mortar or Cement Bed (http://www.sterlingplumbing.com/onlinecatalog/pdf/1049440_2.pdf) (optional)


Remove the receptor from the alcove. Remove the felt pad if present.
NOTE: The receptor supports must rest directly on the subfloor. Build a dam to keep the flooring material clear of the drain area.
NOTE: Do not use gypsum cement or drywall compound for this application, as they will not provide an acceptable, durable bond. Use cement or mortar.
NOTE: Do not spread cement or mortar around the receptor feet.
Spread a 2′′ (5.1 cm) layer of cement or mortar on the subfloor.
Remove the dam.
Position a piece of plastic drop cloth material on top of the cement or mortar bed.
Move the receptor into position.
Verify that the receptor is level and resting on all supports.
Clean the receptor to reduce the risk of surface damage.
Position a clean drop cloth or other similar material into the bottom and over the outside edge of the receptor. Be careful not to scratch the surface of the unit.

Cheers

Gasser
01-01-2010, 04:12 PM
I've been reading through this thread and I am unclear on whether or not it applies to my partcular tub...

I'm installing a Maax Picadilly tub (air jet not whirlpool but similiar construction). It has 2 - 2x4's molded in that run the length of the tub. They are on edge so the tub is raised about 3.5 inches off the floor at it's lowest point.

The instructions...which are somewhat generic and not specifically for my model say that you can use mortar or shims to help level and secure the tub. I get the use of mortar in my case to help level but the discussions about it supporting the tub I am not clear on. Is what's being said in this thread that I should have a layer of mud 3.5" thick under my tub? I'm not disputing it...just seemed like a lot so I thought maybe the tubs you are talking about rest more or less directly on the ground with the feet only serving to support where the tub bottom curves.

Along the same lines...if I use mud for leveling (and possible support) how do I account for the thickness of the mud when building the frame around the edges of the tub?

Thanks!

BimmerRacer
01-26-2010, 07:50 AM
Whats the reason for plastic on top of the mortar bed? Also, can the mortar bed be contructed similar to a shower, i.e. tar paper, lath, mortar?

jadnashua
01-26-2010, 10:01 AM
Some people prefer plastic on top of the mortar to keep it from sticking to the tub. Something on the subfloor to prevent it from wicking the moisture out is a good idea. Generally, you don't need lath as you don't have any point loads, the body of the tub spreads it out. You don't want to pack your mudbed down like in a shower...you leave it loose, then settle the tub down into it until it is at the right level and plumb. In fact, you can use mounds of the stuff so when you do smush it down, it has somewhere to go more easily - the mounds spread out and provide the required support.

BimmerRacer
01-26-2010, 10:08 AM
Jim, thanks!

Terry
01-26-2010, 03:23 PM
If you could drop a tub into place and the bottom of the tub perfectly touched the floor at four points, you wouldn't need shims or addtional support.
However, what a shame if you tiled up the box, and the tub sets up even 1/4" of an inch. Then what?
What do you do with the gap?

I like to plan for about 1" under the tub.
Then I put a few piles of mortar down, and let the tub squish the piles.

If you try to make a perfect bed for the tub, it will not spead and let the tub conform as needed.
You may wind up with a tub setting up 1/4" or more above the deck.

The piles allow for spreading.
It's the same reason that trowels for tile have notches.

Gasser
01-28-2010, 09:50 AM
Thanks Terry that really helps! I am confused on 1 point and want to make sure I have this right...

This is an alcove installation with a tub supported by 2 - 2x4's running the length of the tub...I will use some 1x3's to create a level surface on 3 walls to support the edges of the tub about an inch higher than the tub. Then put mortar down and I'm assuming if I make two rows of motar to match the 2x4's on the tub this would still accomplish the whole squishing thing.

Next I set the tub in place so that the edges rest on the 1x3's around the edge....and this is where I'm confused. The edges are not meant to support the weight of the tub. If I push the tub in until it solidly rests on the edges will the mortar underneath set up and not shrink when it dries? If it does that would put some pressure on the edges to support the tub. Also, I've read where people recommend filling the tub with water to make sure it is pushed down good in the mortar. Wouldn't that put more pressure on the edges by pushing the tub deeper into the mortar?

Also, using the method you describe, as long as I build the frame perfectly level then I don't really need to worry about leveling the tub so to speak do I? If the tub is resting on the edge all the way around it will be level and the mortar will take care of any issues with the base/floor not being level correct?

Thanks for your help!

jadnashua
01-28-2010, 10:19 AM
I'd forget that those stringers attached to the tub are even there and put my mounds of mortar spaced around the bottom of the thing. No need to try to match their position with the mortar. Then, assuming your ledger boards are indeed level, push the tub down so the lip touches all around. Note, the tub might be skewed a little, and could rack or twist or could be already. Unless you use too much water to mix the mortar, it shouldn't shrink as it cures.

Gasser
01-29-2010, 04:41 PM
Thanks! So basically the weight of the tub itself will be resting on the ledger boards correct? Then when I fill the tub with water that weight is taken on by the mortar since of course it won't flex.

This really helps... starting to make some sense now!!

jadnashua
01-29-2010, 04:56 PM
The weight of the tub should be resting on the bottom - that would be the mortar (or the embedded stringers). The more you can spread that load out, the less likely you will have any flex in the tub. The fact the edges are touching the ledger boards is good and they are there to support the edges if, for example, someone were to sit on the edge, not to hold the tub up. There should be no weight on the edges at the ledger board...the weight should be on the bottom. Depending on the person stepping into the tub, you could have a point load of many hundreds of pounds on say the ball of one foot. Flex is not good for plastic materials...eventually, they fatigue and can crack or craze. The support supplied by the mortar spreads that load out and prevents those fatigue issues. It's worse on fiberglass with just a jell coat, but will happen with acrylic as well, but probably take longer to notice.

Gasser
01-29-2010, 05:04 PM
The reason I was thinking the weight of the empty tub would rest on the ledgers is because I'm assuming the tub will sink in the mortar before it cures to the point that the ledgers take on that weight and stop it from sinking. Does the mortar not have that much give to it or should I be propping up the tub until it cures to stop it from sinking too much?

Thanks for all your help Jim!

jadnashua
01-29-2010, 05:20 PM
If you used concrete, it might sink...if you use deck mud, probably not. If you settle the thing down until it just is touching the ledgers all around, you shouldn't need to prop it up while it cures. In reality, think of the tub as a boat. It will 'float' on the mortar...you want to ensure good contact and coverage, so you put enough in so you can mush it down to the proper level. The prepackaged deck mud or sand mix is a 3:1 sand/cement mix (usually). If you were going to be building a shower, you'd probably use closer to a 4-5:1 mix. The higher amount of cement in the package means it will smush more than that used in a shower. Deck mud is much closer to wet beach sand than concrete...you don't pour it, you place it (and it stays!). There's no worry about deck mud running; just mix it well, and not too wet.

johnfrwhipple
12-18-2011, 06:35 PM
Here isa look at a recent tub that was set on a project I'm working on.

The framer set a few 2"x4"'s to help make a dish for the mortar mix.

Like Terry mentions the tub will settle and the mortar mix will spill over.

Myself I prefer to use a little plastic or vapour barrier so you create a bond breaker - this way if the tub is needed to be removed it can be removed with a lot less hassle.

JW

http://i839.photobucket.com/albums/zz314/jfrwhipple/Setting%20a%20tub%20into%20a%20mortar%20bed%20for% 20extra%20strength/Backframingforamortarbedtubinstallations.jpg

http://i839.photobucket.com/albums/zz314/jfrwhipple/Setting%20a%20tub%20into%20a%20mortar%20bed%20for% 20extra%20strength/Makingatubfillsolidunderfoot.jpg

johnfrwhipple
12-18-2011, 06:35 PM
Deck mount tubs and tubs not equip'd with showers still need waterproofing measures. This is often skipped in renovation projects and can lead to costly repairs.

Installing waterproofing to the tub deck before installing the tub is ideal but often it is not practical in new construction. Installing a sheet membrane like Kerdi, Dural, Protegga or Noble can be a challenge and you will find that a liquid membrane and a small brush will work well.

Often these tubs are set on little stand offs or scrap pieces of plywood. I like to leave them in as long as possible and then catch the waterproofing up once most of the tile is installed and the blocks are removed.

Since the water has no place to go once spilled on a tub deck an epoxy or urethane grout makes perfect sense. If that is not practical then building a small lip into the tub deck can help.

Sheet membranes tend to wick water a few inches. All of them. So again if you are using this tub for your kids you might consider a liquid as your best approach.

Red Guard,
Aqua Defence
HPG
Hydro Ban

all good options - pick the one that manufactures the setting material you will be using.

Here is a look at a tub surround we did with Mapei HPG - this tub is not a deck mount and I tied the waterproofing from the tub right to the wall and niche.

http://i839.photobucket.com/albums/zz314/jfrwhipple/Waterproofing%20a%20stand%20alone%20tub/Screenshot2011-08-01at80632PM.png

http://i839.photobucket.com/albums/zz314/jfrwhipple/Waterproofing%20a%20stand%20alone%20tub/Screenshot2011-08-01at80651PM.png

http://i839.photobucket.com/albums/zz314/jfrwhipple/Waterproofing%20a%20stand%20alone%20tub/Screenshot2011-08-01at80703PM.png

ballvalve
12-20-2011, 10:33 AM
If you used concrete, it might sink...if you use deck mud, probably not. If you settle the thing down until it just is touching the ledgers all around, you shouldn't need to prop it up while it cures. In reality, think of the tub as a boat. It will 'float' on the mortar...you want to ensure good contact and coverage, so you put enough in so you can mush it down to the proper level. The prepackaged deck mud or sand mix is a 3:1 sand/cement mix (usually). If you were going to be building a shower, you'd probably use closer to a 4-5:1 mix. The higher amount of cement in the package means it will smush more than that used in a shower. Deck mud is much closer to wet beach sand than concrete...you don't pour it, you place it (and it stays!). There's no worry about deck mud running; just mix it well, and not too wet.

This is the correct way. Wet mortar is futile because of high shrinkage. Must be damp beach sand to stop over shrinkage. The guys that get a bag of plaster really have it right because it EXPANDS when setting.