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I want to build this: http://www.mrmoneymustache.com/2012/12/21/how-to-make-a-relatively-sweet-shower-cheap/

and I'm building in my basement bathroom: on top of the foundation I have 2x4 (horizontal) making joists (space about 4-6" apart) and the 3/4 plywood to make the sub floor.

So my question: is 3/4'' sufficient?

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The 3/4 sub sub floor is sufficient.

I have some comments about Redguard on the shower floor.

While the product (and others like it) is rated for a directly-under-the-tile waterproofing, I have some cautions (directed at the installation in the DIY blog article) :

Be sure you do a minimum of 2 coats, at right angles (as recommended). Be sure you lightly hone the cement base with a rubbing block, for a bump-free surface, before coating. If you have any voids, fill them in with the thinset you will use, before coating (using a portland cement thinset, not a premixed mastic thinset)

Be aware that the unprotected Redguard IS NOT abrasion, scuff or scratch resistant. A dropped tool or tile will cut it. Be very careful walking and kneeling on it..

Consider using a sheet membrane product (Kerdi, NobleSeal TS) for the floor and using Redguard on the walls only. I would put the Redguard at least 4ft high on the walls or a foot higher than wherever the direct spray would hit the wall opposite the spray head (whichever is higher).

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any thoughts on blueseal? A tile/flooring person at Home Depot said almost the same thing so she recommends blueseal – cbrulak Aug 14 '13 at 15:00
I think the blog article is good. I have gone concrete, membrane, concrete, then redguard. I will say this - the smoothing out the concrete on the top layers is an art that I have yet to perfect. I always have to do a little rough sanding... On the redguard application - if you have used it before - from his picture in the blog - it looks like he caked it on. Maybe 3-4 coats. – Tom Aug 14 '13 at 16:10
I think the idea is very interesting. I have used redguard to triple seal some shower walls... I would like to see more info on using it for pans. I would definitely think about this method in a basement bathroom - and a lot of times shower drain in basement bathrooms don't lend itself to finding a pan that fits. – DMoore Aug 14 '13 at 16:40
No experience with Blue Seal. 5 min tour didn't turn up any negatives. Couldn't find any hard comparison data. Redguard has been on market a while... – HerrBag Aug 14 '13 at 16:56
I have used Redguard for many many bathroom walls and it isn't bad. I like to "test" things out a bit and I have sprayed the hell out of redguard over drywall with no moisture at all going through. I guess the next step is to make a little drywall box (some material that will mold easy) paint on redguard and fill it with water. Don't have any leftover redguard on me right now. – DMoore Aug 14 '13 at 17:13

Yes, 3/4 inch plywood (not particle board, MDX, or whatever) is a standard subfloor in quality construction.

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