Confused about mortar under tubs...

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Reach4

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Thanks Onokai, got it
Don't make big piles that you might tend picture for garbage bags. You want support over a big area, but you want easy expansion sideways during compression. That pretty calls for a pattern of separated piles, or strips.

Now if garbage bags were being used as if the were two sheets of plastic, that would be ok.
 
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Terry

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I use the ledger board. It helps for leveling too. That goes in level, I mark down from that to see if I will need to shim the apron, and then the mortar if used helps to make the tub feel solid.
Sometimes if all conditions are perfect, the tub doesn't need anything. Other times, I might use some adhesive on the floor, and finally there are times when the gap is too large for those ways, and mortar is used.
 

MTy

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Tomorrow I'm going to be setting my 30x60 Kholer underscore acrylic alcove tub. The tub is level but I plan to use mortar for support.

1. How many bags of mortar? I've got one but not sure if I need a second.

2. What consistency am I looking for in the mix?

3. How big should the piles be? A few large ones or a bunch of small ones?

4. Any other advice?
 

Lordoftheflies

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Tomorrow I'm going to be setting my 30x60 Kholer underscore acrylic alcove tub. The tub is level but I plan to use mortar for support.

1. How many bags of mortar? I've got one but not sure if I need a second.

2. What consistency am I looking for in the mix?

3. How big should the piles be? A few large ones or a bunch of small ones?

4. Any other advice?

I feel like everything you asked is in this thread already.

That said, I would get more bags of mortar than you think you need. Ask me how I know this.

Consistency, as others have said I'm sure, is like moist sand, but more sandy than moist. You don't want a soupy consistency, you want it on the dry side.

The more area you have in contact with the mortar, the better. I did a large area on the end opposite of the drain and feeling like it wasn't enough after I set it, I laid down and shoved in more near the drain.
 
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Terry

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I normally use 1/2 bag of mortar.
What size and how many depends on the space you are working with. More spots is always better, but not so much that the tub or shower won't drop down all the way to where you want it.
 

Procarp john

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I worked with a company that set alot of tubs, probably the most in the country. Inside scoop was over time they we're getting callbacks from squeaks or cracking noises. so we stopped using mortar and started using 20 minute hot mud, one bag.
 

Self Learner 16

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I am installing a bathtub for the first time -
American Standard 2425VC-LHO.020 Evolution 5-Feet by 32-Inch Left-Hand Outlet Whirlpool Bath Tub with EverClean, Hydro Massage System and Integral Apron, White.

The instructions say it needs a mortar bed. On the apron side there is 3 inch gap from the ground to the plank and on the other end of the plan there is only a 2 inch gap.

Subfloor is wood plank (not very level) and I put over an Advantech board (very level and cut to size) and I painted it with Varathane poly-urethane (oil-based) clear gloss (according to Advantech instructions) so you can see the screws.

My concern is that 3 inches of MAPEI mud bed mix spread over at least 4x2 feet will be very heavy.

So I was thinking to use the leftover from Advantech and cut 2 pieces 4 x 2 - approximately where the mortar bed will be - paint them with poly-urethane like I did for the floor and then screw them over the existing Advantech floor to raise the bed for about 1.5 inches (23/32 x 2 = 46/32 inches ~= 1.5 inches)

This will cut 1.5 inches from the height of a mortar bed needed- so the total weight of the mortar bed needed will be less than half.

Is this a good idea ?
 

Tuttles Revenge

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I am installing a bathtub for the first time -
American Standard 2425VC-LHO.020 Evolution 5-Feet by 32-Inch Left-Hand Outlet Whirlpool Bath Tub with EverClean, Hydro Massage System and Integral Apron, White.

The instructions say it needs a mortar bed. On the apron side there is 3 inch gap from the ground to the plank and on the other end of the plan there is only a 2 inch gap.

Subfloor is wood plank (not very level) and I put over an Advantech board (very level and cut to size) and I painted it with Varathane poly-urethane (oil-based) clear gloss (according to Advantech instructions) so you can see the screws.

My concern is that 3 inches of MAPEI mud bed mix spread over at least 4x2 feet will be very heavy.

So I was thinking to use the leftover from Advantech and cut 2 pieces 4 x 2 - approximately where the mortar bed will be - paint them with poly-urethane like I did for the floor and then screw them over the existing Advantech floor to raise the bed for about 1.5 inches (23/32 x 2 = 46/32 inches ~= 1.5 inches)

This will cut 1.5 inches from the height of a mortar bed needed- so the total weight of the mortar bed needed will be less than half.

Is this a good idea ?

Way late, but yes. Adding wood or whatever you used to your subfloor to reduce the live load/weight is a good idea.
 

Eagle4x

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The guy who helped me with converting a bedroom to a master bath used drywall mud under the tub and the mud cracked and I removed it and put sand. I don't understand why using mortar better than sand because if tub ever has to be replaced:

1) More difficult to remove.
2) It will be damaged while removing it and therefore not able to resell it.
 

Reach4

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The guy who helped me with converting a bedroom to a master bath used drywall mud under the tub and the mud cracked and I removed it and put sand. I don't understand why using mortar better than sand because if tub ever has to be replaced:

1) More difficult to remove.
2) It will be damaged while removing it and therefore not able to resell it.
0. Sand can shift. Bounce up and down for a while in your plastic tub on sand, the sand piles can move. And if you were thinking of a flat bed of sand, that would be nearly impossible to get the right amount of sand.
1. You can put balls of mortar into sandwich bags, and they would be easily removable if you remove the tub.
2. Really? Have you ever sold a used tub?
 

Onokai

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I used cement but mortar would be the same -I put it in heavy duty trash sacks so its not sticking to floor or tub/shower. sand is no good as it will just work loose. You need firm contact support-mortar or cement enclosed in plastic -let it set off before getting into tub.
all of your points do not hold up
difficult to remove -not its in a bag so pick it up and throw it out
resell it sure the mortar or cement is great for resale since its in a bag you can move it to someone's truck-just do not tell them its went off decades ago
and a bonus is the tub will resell as well as nothing is sticking to it.
 

Eagle4x

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0. Sand can shift. Bounce up and down for a while in your plastic tub on sand, the sand piles can move. And if you were thinking of a flat bed of sand, that would be nearly impossible to get the right amount of sand.
1. You can put balls of mortar into sandwich bags, and they would be easily removable if you remove the tub.
2. Really? Have you ever sold a used tub?

My jacuzzi tub is secure on a frame and has 2" thick styrofoam block in different locations under it and I put sand between them, so there is no significant movement of the tub. My understanding is that the purpose of installing something under the tub to keep floor of tub from cracking. However, putting mortar in ziplok bag and putting under the tub is a good idea but I hate mixing it, so in your opinion would either of the following work ok:

1) Using mastic in ziplok bags?
2) Wedging 2" pieces of rigid insulation under the tub?

As for reselling a used tub, the one I purchased is used...a $1,500 tub I bought for $100 because the seller said it would fit in their bathroom...works great. I sell them for sale frequently on craigslist, etc.
 

Reach4

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I don't know mastic. If it needs air to cure, it would not work in plastic bags.

As for mixing, you buy mortar mix. Thinking about it, I guess you could put a measured amount of mortar mix into a bag and a measured amount of water. Then knead the bag. My comment is not based on experience.

As far as rigid insulation, how do you get the thickness right? With balls of mortar, that self-sizes.

Now if retrofitting from the side, maybe you could put some foam wedges in. But I think you could alternatively stuff bags with balls of mortar in from the side.
 

Onokai

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I don't know mastic. If it needs air to cure, it would not work in plastic bags.

As for mixing, you buy mortar mix. Thinking about it, I guess you could put a measured amount of mortar mix into a bag and a measured amount of water. Then knead the bag. My comment is not based on experience.

As far as rigid insulation, how do you get the thickness right? With balls of mortar, that self-sizes.

Now if retrofitting from the side, maybe you could put some foam wedges in. But I think you could alternatively stuff bags with balls of mortar in from the side.
The idea is to make the tub bottom firm so it does not flex. Any way you get to this is fine. The bagged mortar or cement is the easiest-add water mix and bag and install. all, the other ideas are harder and take more time. Figuring foam thickness is too hard as you cannot measure under the bottom. If you can firm up the floor with your ideas then fine. The standard is mortar or cement in a bag. I have do a few of these in stand up showers and its quick and easy and it works to make the floor a solid mass when its sets off.
 

Tuttles Revenge

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There are a million complicated and dubious ways to install a tub. The best way is one in which it is easily and inexpensively performed and lasts longer than your warranty or your personal use.

As a professional, we have found that that is accomplished by applying Type S mortar either as strips or individual mounds that will contact the tub and slump down only as far as the tub pushed them down. A thin sheet of painters film plastic over the top ensures the mortar doesn't adhere to the tub in case we need to remove the tub for some reason usually only needed on drop in soaking tubs.

There are numerous reasons to place mortar under a tub or shower pan, but the most obvious reason is to keep the tub from flexing which can destroy its structural integrity or damage the seal and cause a leak.
 

FranMC

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There are a million complicated and dubious ways to install a tub. The best way is one in which it is easily and inexpensively performed and lasts longer than your warranty or your personal use.

As a professional, we have found that that is accomplished by applying Type S mortar either as strips or individual mounds that will contact the tub and slump down only as far as the tub pushed them down. A thin sheet of painters film plastic over the top ensures the mortar doesn't adhere to the tub in case we need to remove the tub for some reason usually only needed on drop in soaking tubs.

There are numerous reasons to place mortar under a tub or shower pan, but the most obvious reason is to keep the tub from flexing which can destroy its structural integrity or damage the seal and cause a leak.
Golden words. Due to my practice, sometimes better to call the pros, no matter how shameful it may sound. Once I've faced with installation of it...
 
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