I have an older (15+yrs) fiberglass tub, the floor is flexing like you would not believe. It's fine for the kids I guess however when adults get in they can feel the flexing. My only access is from the access panel at the drain end. I don't see any support under the tub at all. I realize the tub needs to be replaced however that is not an option at this point in time. How can I add additional support to the tub floor, spray foam?

Hi...

If there is NO support under that tub then you may be able to open up the ceiling from below and strengthen the floor from underneath. Foam will not work if there is no support to support the foam... right?

Otherwise, I'd rip that tub out. I have seen the result of a person falling through a tub with no support underneath... lucky she wasn't killed.

Let me know if that makes sense?

MARK

" I dont see any support under the tub at all." well what do you see, is there floorboards under the tub or just open to the ceiling cavity below?

The tub is a three sided enclosure type all one unit, I do have a solid plywwod floor under the entire tub with the exception of the drain area. . The tub part of the unit is not touching the floor at all, in the area of the drain it is about 1 1/4 inches off the floor, near the center or as far as I can reach the tub is about 1 1/2 - 1 3/4 off the floor. The tub's front (as if getting in it) is touching the floor the entire length.

I have read several postings of people using the spray foam however other have indicated that it will fill the gap however compress as soon as it is used, so I am thinging it is a waste of time.

You are correct. Foam consists of air bubbles that will compress over time. Supporting the tub floor in called "bedding the shower/tub floor" and we accomplish this by puddling cement or mortor into a ball and placing around various spots under the tub. Let it set up and cure before you put any weight back into it. Several problems can develop if a fiberglass or plastic shower or tub isn't bedded.
1) over time cracks will develop in the floor due to the flexing **and**
2) if it flexes around the drain, eventually it will rupture the drain seal and develop a leak.
I would bed the tub as soon as possible to avoid any future problems. Good luck, Tom

Tom is correct, do not use foam, great for insulation but not as a bed for fixtures. By now you are probably realizing that the installer knew little about installing a fiber glass tub, this was a critical and foolish mistake. Balls of mortar or modified thinset will be pretty messy trying to shove them under the tub but nobody will ever see the mess. Although I have never done this I think I have an idea worth considering. Make basebal sized globs of either mortar or modified thinset and wrap in a 6x6 sheet of cheese cloth. The cloth will help keep the ball intact while you shove it in with a stick made like a shuffle board pusher. I'd try to get atl least 30+ balls in under the tub and then do not put any weight in the tub for a week to let the mortar completely set up.

Tom is correct, do not use foam, great for insulation but not as a bed for fixtures. By now you are probably realizing that the installer knew little about installing a fiber glass tub, this was a critical and foolish mistake. Balls of mortar or modified thinset will be pretty messy trying to shove them under the tub but nobody will ever see the mess. Although I have never done this I think I have an idea worth considering. Make basebal sized globs of either mortar or modified thinset and wrap in a 6x6 sheet of cheese cloth. The cloth will help keep the ball intact while you shove it in with a stick made like a shuffle board pusher. I'd try to get atl least 30+ balls in under the tub and then do not put any weight in the tub for a week to let the mortar completely set up.


Thanks to all of your responses, I like the idea of using cheese cloth I would think it would assist in forming and filling the entire voild under the tub floor. I should also attempt to cover the subfloor area under the tub with plastic as well.

I would advise to NOT use plastic under the tub. It will prevent any possible bonding of the thinset with the floor. I think enough thinset will weep through the cheese cloth to make a bond to the floor and the tub.

We have faced same problem several times before. We managed to insert, and wedge in, a 2' long pieces of 2"x 4" under the tub, one on each side of drain. We kind of gently hammered it it. It solved the problem.

When I have run into that problem we expose the end of the tub and use structo lite not mortar or and thinest. The cheese cloth is a good idea bal. Very creative.

Structo lite is what I always use to set a tub or shower. Just don't jam up access to the drain.

Never had a cracked tub yet using it. It sets up faster then reg mortar and isn't heavy for the floor

STRUCTO-LITE® Basecoat - USG Corporation (http://www.usg.com/navigate.do?resource=/USG_Marketing_Content/usg.com/web_files/products/prod_details/USG_Structo-Lite_Plaster.htm)

Needgameplan. If you can get under it and pack in some structo lite, the tub bottom will be solid as a rock.

Call your real masonry supply house and they should have it.

Signed 21 Boat

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The problem with packing in wet cementous mix of any kind is that he will not be able to push it all the way against the bottom of the tub. There will always be a gap. At least, that's what I've learnt over the years...

Hi all..

Funny that boat21 mentioned the structolite gypsum... also all I ever use to set my tubs and showers in... usually found at home depot today, a plaster supply company OR a masonry supply store.

Milo, this material grabs things unlike any cementous product on the market... it is actually a PERLITED GYPSUM PLASTER... has a tendency to grab and stick. I actually use a trowel or a shingle and pull excess up the sides of the shower or whirlpool tub to just lock them in place forever.

Bob's idea of the cheescloth would really add structural strength!

Another great point raised is that this stuff dries overnight. Hope you all try it someday... :)

MARK

Mark you point out one big difference I did not know. Modified thniset tales days to cure, I mat start trying your structolite gypsum on my next project. I use thinset because it is the same stuff I then use to set the tiles.

The cheese cloth would not be necessary at all for a new install. It's a great Idea for getting it under a tub to be able to Push it in.

For new install structo smashes well to set a tub or shower base. I set them the night before and nail flanges the next day. The perlite makes it such a Lite material to work the base units down. Next day its like concrete. 48hrs can jump on it and won't crack.

Bal1 Also I use Structo lite for plaster repair or drywall repair. Mix tsome structo lite in your drywall compound in the tray. You can now apply in a deep hole or on a brick wall where the platers has fallen out. It sets overnight and no shrink cracks. Now it ready for a finish coat of reg compound. Even with fast sets Depth becomes an issue. Not to mention expense as opposed how far a bag of Structo goes.

Little Re hap secret


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Hi all..

Funny that boat21 mentioned the structolite gypsum...also all I ever use to set my tubs and showers in...usually found at home depot today, a plaster supply company OR a masonry supply store.

Milo, this material grabs things unlike any cementous product on the market...it is actually a PERLITED GYPSUM PLASTER...has a tendency to grab and stick. I actually use a trowel or a shingle and pull excess up the sides of the shower or whirlpool tub to just lock them in place forever.

Bob's idea of the cheescloth would really add structural strength!

Another great point raised is that this stuff dries overnight. Hope you all try it someday...:)

MARK

Hmmm... did you say "grab and stick".. Those are the two best qualities my wife has ! :D:D:D

Tom is correct, do not use foam, great for insulation but not as a bed for fixtures. By now you are probably realizing that the installer knew little about installing a fiber glass tub, this was a critical and foolish mistake. Balls of mortar or modified thinset will be pretty messy trying to shove them under the tub but nobody will ever see the mess. Although I have never done this I think I have an idea worth considering. Make basebal sized globs of either mortar or modified thinset and wrap in a 6x6 sheet of cheese cloth. The cloth will help keep the ball intact while you shove it in with a stick made like a shuffle board pusher. I'd try to get atl least 30+ balls in under the tub and then do not put any weight in the tub for a week to let the mortar completely set up.


Update, What a great idea of using the cheese cloth.

I think the flexing issue will be a thing of the past thanks to your advise.
I was not able to do this from the drain end of the tub. Thankfully I have another bathroom on the other side of the wall and the vanity was at the other end of the tub. I removed the vanity and cut open the wall. I actually cut the cheese cloth so that it was just as wide as the tub bottom and trowed in the cement and wrapped it in the cheese cloth the first two went with out a problem the remaining started to unwrap as I pushed them in. However it worked much better then trying to push in the mortar by itself. I also used a quick drying and non shrinking type of mortar which dries in an hour. It has been two hours and I tapped on the tub floor and I think I may have gotten 95% of it supported.

Thanks again for you advise.

Glad things are working out for you. Come bacl anytime

Have you thought about using low exansion foam insulation which is sprayed out of a nozzle from a can? The same type used to insulate around windows during the install process? This material dries rock hard and forms naturally to the bottom of the tub.

Hi Scoooter...

Any expansion foam, including low expansion foam, is not advised for use as a bedding substrate for tubs/showers as the foam has a tendency to compress over time and can eventually lead to voids/pockets underneath the unit.

In fact, many manufacturers state very clearly in product installation instructions that any expanding foams used will void product warranty.

As always, it is best to follow the instructions of the particular tub/shower being installed.

Thanks...

Mark

Scooter,
You're responding to a year old thread and your advice was faulty. Mark explained why. Tom