Bathtub leveling with mortar - Minimum thickness?

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Bmusgrove

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I am installing a Bootzcast tub as part a remodel. This tub has the self leveling foam pad attached to the bottom.

When the tub is installed in the alcove on a level ledger board, and the tub level front to back and side to side (measured at the front, middle and back) there is a gap on the back right corner where the foam pad does not sit on the floor, If measured the gap at the corner is 1/4 of a inch and extends towards the front of the tub about 6 inches gradually narrowing to zero. . Side to side across the back it extends about 4 inches before the gap narrows to zero. Its off something squished the foam on a diagonal across that back corner.

My Options -
1: Leave as is until my OCD forgets about it,
2: Use mortar to fill that gap, as suggested by the manufacturer. Would a bed of mortar that thin in the corner support it? Seems a mortar base that thin wouldn't support enough weight to keep from crumbling
3: ??????

Edit: The floor is level. Part of the remodel was fixing rotted subfloor, and fixing a ridge caused by a sub floor joint. The section was cutout, leveled by sistering 2x10's to the joists as needed, and then a single piece of 3/4 OSB was installed.
 
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Reach4

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2: Use mortar to fill that gap, as suggested by the manufacturer. Would a bed of mortar that thin in the corner support it? Seems a mortar base that thin wouldn't support enough weight to keep from crumbling
Mortar in compression is a lot stronger than in tension etc. Manufacturer recommends this action. No reason not to. Don't try to fill the gap with a layer. Instead make piles of stiff mortar that gets squished. Fill the tub with water and leave the water while the mortar sets. Put a pile of leftover mortar in a plastic bag so that you can gauge the hardening. My comments are not based on my experience.

Search this forum for mortar piles.
 

Jadnashua

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IF you take a straightedge, are the places where there's a gap the result of the subfloor making a dip, or is it that the bottom of the tub isn't consistent or the floor's not level?

If you can see dips in the subflooring, what is the size of the area that needs to be filled? That thin, if they're dips, I'd consider using something like Ardex's Liquid Backerboard to fill them in.

Does the tub sit level otherwise?
 

Bmusgrove

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IF you take a straightedge, are the places where there's a gap the result of the subfloor making a dip, or is it that the bottom of the tub isn't consistent or the floor's not level?

If you can see dips in the subflooring, what is the size of the area that needs to be filled? That thin, if they're dips, I'd consider using something like Ardex's Liquid Backerboard to fill them in.

Does the tub sit level otherwise?

The foam pad on the Bottom of the top is not consistent. The floor is level front to back side to side and diagonally. No dips checking withh a 4 foot level for a straight edge, Either visually, using a wooden shim, or by turning off the lights and shining a flash light along the edge.
 

Bmusgrove

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The foam pad on the Bottom of the top is not consistent. The floor is level front to back side to side and diagonally. No dips checking withh a 4 foot level for a straight edge, Either visually, using a wooden shim, or by turning off the lights and shining a flash light along the edge.

Using a Empire True Blue 4 foot digital level, the tub is level side to side at the front, middle and back, and level front to back on the right side. By level it is 0-0.05 degree, and that is only at the front measuring side to side. All other measurements are zero degrees. Yes I did calibrate the level per the manufacturers instructions.
 

Bmusgrove

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Mortar in compression is a lot stronger than in tension etc. Manufacturer recommends this action. No reason not to. Don't try to fill the gap with a layer. Instead make piles of stiff mortar that gets squished. Fill the tub with water and leave the water while the mortar sets. Put a pile of leftover mortar in a plastic bag so that you can gauge the hardening. My comments are not based on my experience.

Search this forum for mortar piles.


I should have clarified that.. The manufacturer support line says "lift the tub a little and shovel some mortar in that spot". my concern is at that thickness the mortar will not hold after repeated use. That it will eventually crumble.

Additional clarification: The section in question would be triangle with roughly 6 x 6 legs. starting gap thickness is a hair smaller than a plain jane 13x13 porcelain wall tile gradually tapering in a wedge shape as you go further under the tub.I estimate you have to go about 6 inches under the tub before the pad on that corner makes full contact.
 
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Jadnashua

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It sounds like that area is low, but if it were high, the rigid foam might be able to be sanded so it was flat. I think I might try to use some filler if it's a small area to make the surface flat and not deal with the floor since it is already flat and level.

Some of the floor patching materials are designed to be installed thin and to be able to go to a feather edge. Regular mortar, generally has not got much strength that thin. Deck mud is more like wet beach sand, and doesn't really flow, and needs some thickness over a wooden subfloor for strength. I might consider some thinset, and screed it off. This goes against the industry standards, but with it being maybe 1/4" thick, most of them can support that without shrinking and cracking. It would stick to the foam, too. It does not sound like there's a huge area that doesn't make proper contact, and you might even just be able to layer something like some roofing felt, cut sort of like layers of a topographic map's contour lines to fill it in.
 

Jadnashua

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It sounds like that area is low, but if it were high, the rigid foam might be able to be sanded so it was flat. I think I might try to use some filler if it's a small area to make the surface flat and not deal with the floor since it is already flat and level.

Some of the floor patching materials are designed to be installed thin and to be able to go to a feather edge. Regular mortar, generally has not got much strength that thin. Deck mud is more like wet beach sand, and doesn't really flow, and needs some thickness over a wooden subfloor for strength. I might consider some thinset, and screed it off. This goes against the industry standards, but with it being maybe 1/4" thick, most of them can support that without shrinking and cracking. It would stick to the foam, too. It does not sound like there's a huge area that doesn't make proper contact, and you might even just be able to layer something like some roofing felt, cut sort of like layers of a topographic map's contour lines to fill it in.
 

Bmusgrove

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It sounds like that area is low, but if it were high, the rigid foam might be able to be sanded so it was flat. I think I might try to use some filler if it's a small area to make the surface flat and not deal with the floor since it is already flat and level.

Some of the floor patching materials are designed to be installed thin and to be able to go to a feather edge. Regular mortar, generally has not got much strength that thin. Deck mud is more like wet beach sand, and doesn't really flow, and needs some thickness over a wooden subfloor for strength. I might consider some thinset, and screed it off. This goes against the industry standards, but with it being maybe 1/4" thick, most of them can support that without shrinking and cracking. It would stick to the foam, too. It does not sound like there's a huge area that doesn't make proper contact, and you might even just be able to layer something like some roofing felt, cut sort of like layers of a topographic map's contour lines to fill it in.


Unfortunately the floor does not have a low spot. Checked it 12 ways from sundown with straight edges and levels. A flat edge on the foam shows a definite curve up on the foam in that corner.
Yes its not a huge area. I would estimate if you took a 8x8 to 10x10 tile and cut them in half to form a triangle
Featheredge - Thank you . I could not remember that word for the life of me. Thats exactly what i would need to do if I filled just that corner.

Roofing felt. I did not think of that. I will explore that option.
 
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