I bought a new acrylic & fiberglass reinforced American Standard tub. The bottom of the tub has a piece of OSB moulded to it. The instruction say to use mortar to set the tub. How will this work with the OSB? It is not packing material. Need some clarity.
Many tubs have OSB or wood on the bottom. I set several piles of mortar down and allow the tub to squish out the piles as it drops into place. The mortar as it drys tends to pull away a bit anyway. You can also lay a sheet of plastic down between the mortar and the tub.
The goal of installing any tub is to get it level and have full contact with the subflooring. If you are really lucky, you may not need anything underneath it. For the vast majority of installations, though, it works out best if you use some mortar to get that full support and make things nice and level. Make sure it is level both L-R and F-B, as doing so makes finishing it up and performance easier/better.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014
I was thinking that the mortar would need to flow into an area with ridges/gaps to provide some stability.
Probably want to use some plastic underneathg the mortar as well as between the mortar and the OSB/tub right?
It appears to. Do I need to change the location of the ledger boards to allow for mortar?
Use the small piles as Terry suggested. Make the mud loose, just enough body to allow it to stand up a little, no so stiff that is will not spread out. About ten piles under the base will do it.
John Bridge, Ceramic Tile Setter :-)