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Unread 06-09-2015, 05:50 PM   #19
...unrepentant, detail focused, over-analyzer.
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Join Date: Jan 2013
Location: Virginia
Posts: 2,832
Originally Posted by AM
why does the plywood have to be AC grade if it is just being used for structural/non-visual reasons? Can I get this cheaper plywood that is D-D grade:
That link is technically not plywood, it is rate as sheathing and has a much lower structural rating.

Your alternate choice for a lower cost underlayment would be CBU ($10 for 3'x5' piece). However, it's not structural and you'll need to to call the various CBU manufacturers (Durock, Wonderboard, etc.) technical support lines to see if they recommend their product for installation over concrete under mud floor. PS: I can see CX shaking his head already.

Originally Posted by AM
May I ask why you feel the Kerdi drain system is better than the regular tile-in-drain system? It does seem popular right now. However I believe the Kerdi drain system can be used on a regular/conventional mortar bed application...
My experience is limited to the Kerdi drain but that's certainly not the only solution. The standard pre-slope / liner / final mud bed is a fine solution and would be very cost effective. I'm sure it would work fine in combination with the CBU/ Redguard water proofing you described. There are a lot of Pro's on the site that will be help you install one too.

You'd still need to install some type of underlayment over concrete to cover that big hole. Davy is a whiz at the mud work, maybe he has a better idea how to deal with it.

Last edited by PC7060; 06-09-2015 at 05:55 PM.
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