I'm adding a bathroom and intainstalling a new tub-shower. The tub is made of vikrell (?) which seems to be similar to fiberglass. The instructions say to put mortar under it for additional support. I've done some research and the internet suggests doing globs of mortar on the subfloor, kinda like cookie dough on a baking sheet, then pushing the tub down onto it. This is where it gets confusing. Some people say put plastic on top of the mortar, so it doesn' fuse to the tub in case it has to come back out. That makes sense. Other people say to put plastic under the mortar if it's on osb, but no explanation why. It seems to me like with plastic on both sides there is nothing to hold it in place. My subfloor is advantech osb. Can anybody clarify this for me?
I also had an idea. If I do want plastic on both sides, why not put the mortar in sandwich bags? Any thoughts?
Keep in mind I have no real experience with this specific subject, just general construction knowledge from my years of commercial construction experience. I would think that the plastic underneath would be for the same reason, to keep it from bonding to the OSB. If it were to bond with the OSB, you would have to cut out the subfloor and replace, it wouldn't scrape up without taking some of the OSB with it. Yours being Advantech, it probably isn't as critical as the Advantech is much sturdier than regular OSB. Baggies sound like a good idea, but they may bust open when you go to smash down the tub.
I've never seen it done like that, all the plumbers I work around just mix the mortar on the subfloor and squish the tub into it. I think it's assumed that if the tub comes out it's getting replaced.
The goal of the mortar isn’t to adhere anything, it’s to support the tub. OSB sucks up water which is why plastic between it and mortar, though I’ve never seen that done. Your goal is to do it as if this is the last time it’s ever being done, not worry about the guy 20 years down the road who decides to redo it.
It's remotely possible it will be you in 20 years, so nothing wrong with plastic top and bottom, but it won't really stick to the tub anyway. A little experiment with slump (mixture) might be worthwhile.
In reply to gearheadmb :
Just put the mortar down on the subfloor. It will not adhere to the wood at all. Thats why concrete forms are made of wood. When it comes time to pull that tub, that mortar will fall apart any way. Kohler tubs come with a felt cloth to put on top of the mortar, but nobody uses it. Makes a good cover inside the tub to make sure those tile guy slobs dont make a mess of your tub finish.
tr8todd said:
In reply to gearheadmb :
Just put the mortar down on the subfloor. It will not adhere to the wood at all. Thats why concrete forms are made of wood. When it comes time to pull that tub, that mortar will fall apart any way. Kohler tubs come with a felt cloth to put on top of the mortar, but nobody uses it. Makes a good cover inside the tub to make sure those tile guy slobs dont make a mess of your tub finish.
I use it. So somebody does. I probably do 10-12 of the kohler/sterling shower bases or tubs a year
