mortar under tubs?

Old 11-20-03, 09:21 PM
Jst is offline
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mortar under tubs?

I will be replacing my steel tub with a acrylic one. I've heard that a dry set mortar should be put on the floor under the tub to prevent flexing. Can someone clarify what this is? Is it the same as tiling mortar?

Also, any tips on how this stuff shoud be applied? How much, how thick, etc.?

Thanks, Jst
Old 11-21-03, 02:26 AM
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I think you're right, might want to post this over in the tile section. Here's a link to the page
Old 11-26-03, 05:59 AM
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Talking Mortar bed

Mortar bed is essential because it supports weight of tub, water and people in it altogether. If you don't have a mortar bed, all weight is exerted on outer edges of the tub and it'll crack.

Thinset mortar used for tiling is sufficient enough; just make it very very thick.
It's harder to mix but you won't have to worry about flowing outward and sagging.

Set the tub in place, mix a batch(you'll need to make several of batches, actually; it takes a lot to fill up the cavity between bottom of tub to floor) and shovel it between bottom of tub and floor. No need to trowel, no need to make it neat; just fill up all space between two.

Let it cure for 2-3 days(I usually leave it along for 5 days).
Old 11-26-03, 06:21 AM
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Just to follow up what the guys have suggested, here is another method that I use. Manufacturers may or may not request a support system but when they do, they recommend either a mortar mix or a joint compound mix. Here is a short article I wrote for others to follow,

Following the directions per the manufacture for installation. Lack of support causes squeaks, in some cases leaks at drain pipe fittings and worst of all cracks in the finish material. Most manufacturers recommend or suggest installing a mortar base support under the tub or shower bottom before setting the tub or shower unit in place. You can use either a bag of Quikcrete or a 5 gallon pail of pre-mix joint compound. ( usually I use the pre-mix 5 gallon...lazy and it's less mess) You can lay poly down under the tub or shower prior to doing this to prevent any moisture issues while this is drying.

When this sets up, usually with 24-48 hours, your tub or shower bottom will be rock solid supported. This does 2 things, prevents any possibility of potential cracking within the fiberglass/acrylic and eliminates any movement at the tub/shower drain assembly or potential leaks that could happen.

Ensure that you do not get any around the tub or shower drain assembly should you need to do anything down the line. In most cases, the holes cut for the drain lines will keep any base support away from it.

Hope this helps!

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