Howdy everyone
I’m installing a Mansfield alcove tub, acrylic whirlpool tub encased in fiberglass.
I have laid 3 mortar beds and I get a “spot” in the middle of the tub that has give. Each time I lay enough to compact, I set the tub in place and allow it to dry, I always wait 2 days for full cure. It get what feels like a soft spot in the exact same place every time. I took a pic of the inside of the tub, I initially outlined the area that gives when I walk/push on it so I could add extra mortar the other two times. Each time the same issue. I get mortar down, verify level and wait.
Today I pulled the tub and placed a level on the underside and lo-and-behold, the osb that is fiberglassed to the acrylic is cupped outward. The gap on the outsides are visible when I hold a level in the center of the osb. W/ the osb having a cup, the plastic will always have a little give on the tub side.
I got the tub last summer but the tear out and several other projects, family emergencies and now the gov shut down has put me behind.Thus i’m beyond the warranty period.
Any thoughts or ideas?
Replies
I will expand further that I did "piles" last time. I made a grid from 1x1's so the mortar could fully bed and shape.
The mortar is shaped to the underside of the tub BUT there is an air gap between the acrylic and the osb so everytime you walk in the tub it has give, it is the acrylic that is flexing, not the osb. The osb is fully supported by mortar.
I've tried to fix the same problem on an acrylic tub without much success. I drill through the OSB base very carefully into the void. I inserted a spray foam nozzle in the gap, filled the tub with water then squirted as much foam as I could in there. It partially worked but I'd say bite the bullet, toss the tub and go get a cast iron one.
I finally got a reply from Mansfield. Their tech is supposed to call me back on monday. A suggestion was made to do similar to yours from the underside, go through the OSB w/o breaching the acrylic. Use fiberglass resin, so it won't case delamination, inject into the cavity and let it sit. It is waterproof and will fill the void w/o any squishing.
At first they said, "Oh these things happen sometimes", This morning they were like "That is unusual". We'll see what Mansfield says on Monday.
Did you fill the tub two-thirds after putting the mortar bed in place? The acrylic tub needs the weight of the water to press into the mortar.
Did you use a true Mortar Bedding product or something else? My local Home Depot has only recently started to carry a mortar bedding product and so I have had to buy it from the nearest Lowe's store in the past. I would also be generous with the amount of bedding mortar used as "too much" is not going to cause any problems.