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We have an upstairs 9x5 bathroom in wooden construction. Ceiling height is 8 feet. Our contractor used a combination of "GoBoard" (concrete-type board) for the shower area, and "blueboard" for the remaining part of the bathroom.

We purchased porcelain tile that is 12x24", 5/16" thickness, and this tile is heavy. Each piece of tile weighs about 8.5lb (so about 4.25 per sq ft).

We'd like to tile from floor to ceiling to achieve a modern look, but don't want backerboard/tile to fail someday down the road, and come crashing down.

The current dilemma is whether to:

A. Scale down the plan and tile only a portion of the wall, perhaps the lower 4 feet.

B. Ask the contractor to replace the "blueboard" with something stronger.

C. Go ahead and tile over the blueboard.

Was hoping someone could suggest ballpark figures of safe/unsafe load and if we're thinking correctly here. Many thanks.

backerboard

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What you have is done all the time. In some cases it is set on regular drywall, a little weaker than the blueboard. The loading tests the shear strength of the screws and glue that holds the drywall in place, if it has it. If it was done like that on the ceiling, it would be a different matter.

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    @isherwood and Jack, does this answer mean that the loading is near the probable shear strength of the blueboard as currently attached? At this point the only thing that could be done is to drive more screws. Do you think that should that be done? – Jim Stewart Jul 9 '17 at 15:39
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    Ordinary drywall is quite strong in shear. It looks adequately fastened from here, but a few extra won't hurt. – isherwood Jul 9 '17 at 15:48
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    What is the spacing of the screws on the GoBoard? If the blue board outside the tub/shower surround is to be tiled, then wouldn't one want the same screw spacing there? One problem with tiling to the ceiling is that this increases the difficulty of fastening towel racks, toilet paper dispenser, clothes hooks, but the fastenings would be more secure. – Jim Stewart Jul 9 '17 at 17:07
  • Thank you Jack and others for your thoughts. If the blue board is secured sufficiently to the studs, would the outer paper layer be a concern (the bond of the board's paper layer to the inner contents of the board being the weakest link?) Would presence of grout in final installation reduce the stress, with lower tiles somewhat supporting the weight of upper tiles? – user7374453 Jul 9 '17 at 21:23
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    Regarding the comment about the paper layer, no the shear strength is tremendous as mentioned by isherwood. If it was a ceiling install, then those layers are stressed in a way they were not designed to be stressed. On the loading of the floor system, yes the load is transferred to the floor by the adhesive/thinset to the wallboard, whatever it may be and the grout picking up loading between the tiles, still transferring everything to the floor system. Now the question lies, what can the floor framing handle? IRC has minimums of construction, the builder may have followed or added to it. – Jack Jul 9 '17 at 21:52

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