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I have put many of them on 3" slabs. For whatever reason, a "4 inch slab" seems to only be just over 3" around here. I guess they figure if a "2x4" can be 1 5/8 x 3 5/8 then anything goes. I would be concerned about the joint between the two - be sure that it doesn't have a raise or bump next to it, which is common. Also be sure the two surfaces are parallel to one another - that they don't slope away from each other.
If the two slabs are as flat as one, I wouldn't worry about it.I don't know if a rubber pad would do anything for you. The plastic pads - I'm assuming you are referring to would help if there was a noticeable gap, change in grade, or bump next to the joint. Otherwise I don't know if it would be worth the trouble and money. If there is one or more of the things I mentioned above, you can also build a simple deck over it and shim and/or level that deck to give the tub a good flat surface. This doesn't have to be anything more than a simple set of boards glued down to the slab with shims as needed. I tend to call this 'building a pallet' to make it seem less intimidating. It does help with uneven gaps or slabs with more 'run' than you would like for your tub. They can be 2x6 laid flat, spaced 2 or 3 inches apart. Screw a 2x2 on the ends to hold them in place and make them look finished - glue them to the slab so they don't move during installation, and so the shims/blocks don't shift. Cut to the exact bottom of the tub, or leave enough hanging out as you desire.HTH
Quote from: Chas on July 29, 2011, 01:04:54 pmI have put many of them on 3" slabs. For whatever reason, a "4 inch slab" seems to only be just over 3" around here. I guess they figure if a "2x4" can be 1 5/8 x 3 5/8 then anything goes. I would be concerned about the joint between the two - be sure that it doesn't have a raise or bump next to it, which is common. Also be sure the two surfaces are parallel to one another - that they don't slope away from each other.Thanks Chas...The two pad do slope a tiny bit obviously for drainage. Not much I would think. Where the pads meet they are level. I plan on having HS dealer come out and evaluating...so I do not run into issues in future with warranty. If I need to do something I'd like to be prepared. Would a rubber/plastic pad help a situation like this at all?