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?

3 Answers 3


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).

  • any thoughts on blueseal? A tile/flooring person at Home Depot said almost the same thing so she recommends blueseal
    – cbrulak
    Aug 14, 2013 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, 2013 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, 2013 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, 2013 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, 2013 at 17:13

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


Do not Red-Guard the entire Shower Floor. Leave approx: 1 foot perimeter around the drain without Red-Guard. If not, any water between the tile and Red Guard near the drain may sit there and develop mold. By Red Guarding the entire Shower Floor area, you run that risk. In My Opinion, of course.

This is providing you have a Membrane just above the leveling Mud layer.

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