# Fiberglass tub cracking sound, fixing with Mortar?



## plumguy (Jun 23, 2005)

markmisky said:


> I just installed a sterling fiberglass tub/ shower surround. It was in an alcove and I was unable to make sure that each foot rested on the floor. The floor was level prior to installing it. I put in a plywood floor with the landscape fabric that came with the tub per the install manual.
> This think sounds like it is cracking anytime you put a lot of weight near the drain or the far end. For example if you shift your weight to one foot instead of two. This is driving me nuts. I read some other posts about this that says it is normal and not to worry but I'd like to minimuze this.
> I was wondering if packing some mortor or thinset under the tub would help. The garage is on the back side of the tub and I could cut an access hole in the sheet rock and pack some morter under the tub. I had thought about using a mortor base but the instructions said it was optional. I was also confused since the manual said not to place mortar under the tub feet? That would be next to impossible to do.
> I'd appreciate any help or thoughts on solving this.


 
Sterling(Kohler) makes a good product. You're right this has been just posted recently. This noise is irritating if happening everytime you use the tub.It isn't putting the tub at risk unless someone is above average in weight(whatever that might be?) or heavy footed. As far as using mortar and you being uncomfortable check with the manufacturer. I have used joint compound in the past(for whirlpools) and it worked great. If you have white tub and use mortar you might see a dark shadow on the bottom as opposed to joint compound being a lot lighter in color. Good luck and let us know how you made out and what the manufacturer said if you call.


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## Duque01 (May 22, 2008)

*Same Problem*

I am having the same p[roblem and am curious if the mortar solution work?


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## stra2d (Jun 2, 2008)

*Kohler Surround Tub - Noise*

The material they provide you is to limit "squeaks" but will not take away the cracking sound. What you need to do is to install a heavy duty rubber mat, you can buy this stuff at Lowes or Home Depot. it's the same stuff the use to install a stand up shower.

Here is a link to what you need.

http://www.oatey.com/Plumber/Shared/ProductGroupDetail/81/PVC+Shower+Pan+Liner.html


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## helpless handyman (Jul 6, 2006)

Hi, try using mortar or thinset under the tub, you can also try Great Stuff insulation as well.

http://greatstuff.dow.com/greatstuff/diy/products/index.htm


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## majakdragon (Sep 16, 2006)

I just love it when manufacturers of acrylic, plastic and fiberglass tubs state that a mortarbed is "optional". To me, optional means, if you don't mind the noise or possible cracking of the material, you don't have to use it. If you have access, use the mortar but make sure you can push it up enough to meet the bottom of the unit or it will not solve the problem. The statement of not placing mortar under the feet is because it could cause twisting or flexing that would damage the unit. The spray-in foam will not solve the problem as it will get crushed down and stay there, defeating the purpose.


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## Termite (Apr 13, 2008)

Majakdragon is right. Packing mortar underneath should really help. I'd also suggest cutting the access hole you described. That way you can do a thorough job. Also, check to make sure that the feet are all tight to the floor. If not, shim them up so they have solid bearing.


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## stra2d (Jun 2, 2008)

*Using Mortar - Vicrel Tub*

Well, the mortar will help with the cracking sound. A couple things you need to be aware of.

1. you need to make sure that you are able to get the mortar under the entire tub area, not just the front or back, otherwise you'll create weak spots where the mortar didn't reach. 
2. I know that there is a product called Structolite that others have used. I'm not sure wher you get it, but I hear that it works well.
3. Rememner that the tubs weight will change dramatically when filled by as much as 200 gallons. Keep this in mind when setting the mortar.

Good Luck!


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## JoshinWV (Dec 17, 2008)

thekctermite said:


> Majakdragon is right. Packing mortar underneath should really help. I'd also suggest cutting the access hole you described. That way you can do a thorough job. Also, check to make sure that the feet are all tight to the floor. If not, shim them up so they have solid bearing.


Ok, I have a question. In the instructions that I received from Sterling, it says that the mortar is optional (uh... NO). It also says that if I use thin set, I need to put a layer of a vapor barrier material between the sub flooring and the mortar. So I have some left over underlayment that was from putting down a Pergo floor in the kitchen. Could I put a layer of this down, then the thinset, then set the tub in it, thus eliminating the squeaks in the tub all together while using the Pergo padding (which has a vapor barrier on it as well) as the barrier?

Thanks in advance, 

Josh


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## majakdragon (Sep 16, 2006)

The vapor barrier is to prevent the moisture from the mortar ruining/rotting the wood flooring out. The wood will suck the moisture out. If the underlayment you have will block moisture from the mortar getting to the wood, go for it.


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## JoshinWV (Dec 17, 2008)

majakdragon said:


> The vapor barrier is to prevent the moisture from the mortar ruining/rotting the wood flooring out. The wood will suck the moisture out. If the underlayment you have will block moisture from the mortar getting to the wood, go for it.


I have to find SOMETHING to do with it. I have an entire unopened roll and some pieces left over to spare. I'll see if I can't use some. Do you know if thin set reacts with the foam on the underlayment?


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## Termite (Apr 13, 2008)

majakdragon said:


> The vapor barrier is to prevent the moisture from the mortar ruining/rotting the wood flooring out. The wood will suck the moisture out. If the underlayment you have will block moisture from the mortar getting to the wood, go for it.


Correcto! If the plywood floor is able to suck the moisture out of the bottom of the blob of thinset then the thinset will be incredibly weak at that location and might crumble. As Majakdragon said, as long as the underlayment is waterproof it will work just fine. _I would caution you, however, that if the membrane can be compressed (foamy material) it wouldn't be a good idea to use it because it will allow movement/flex of the thinset base when someone's standing on it._

You can't go wrong with either plastic sheeting or felt building paper, just to be safe.


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## JoshinWV (Dec 17, 2008)

thekctermite said:


> Correcto! If the plywood floor is able to suck the moisture out of the bottom of the blob of thinset then the thinset will be incredibly weak at that location and might crumble. As Majakdragon said, as long as the underlayment is waterproof it will work just fine. _I would caution you, however, that if the membrane can be compressed (foamy material) it wouldn't be a good idea to use it because it will allow movement/flex of the thinset base when someone's standing on it._
> 
> You can't go wrong with either plastic sheeting or felt building paper, just to be safe.


ah, that was my next question about the foam padding being able to be compressed. Thank you both. I'll put down the plastic sheeting I have then. I have 4 mil thick. Is that thick enough or should I go 6 mil?


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## majakdragon (Sep 16, 2006)

The 4 mil should be fine. No rocks in mortar to tear it and you won't be walking on it.


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## JoshinWV (Dec 17, 2008)

majakdragon said:


> The 4 mil should be fine. No rocks in mortar to tear it and you won't be walking on it.


Thank you kindly sir, I appreciate all the advice.


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## JoshinWV (Dec 17, 2008)

Just a follow up for the tub. I wasn't quite convinced about the plastic sheeting because it would not be directly attached to the flooring itself, so I decided to go to the local Lowe's here and grab a few pieces of 1/4" Hardi-backer (aka concrete board). I installed the concrete board on the plywood subfloor, then the thinset in between the tub and Hardi-backer. Smartest way to go. One, if you have to tear the tub up you don't have to tear your subfloor up; two you can safely secure your tub and reduce any and all flexing and cracking without worrying about subfloor rot.

Thanks for all the insight again!

- Josh


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