Continuing with my complete inability to be brief and concise: ;)

Plywood has four typical face grades; A, B, C, and D. "A" and "B" grades are the best, with "A" having no flaws in the surface veneer, it's good for stain grade cabinetry. "B" has a nice finish, but can have some patches in it to get rid of knot holes in the veneer, it's suitable for paint grade.

"C" and "D" are lesser grades, they are quite a bit rougher than A/B. The "X" refers to the glue being used to glue the veneers together being an exterior rated glue. The glue should not weaken when wet, allowing the plywood to delaminate.

So, for cabinetry or furniture, you'd want AB plywood. For house framing (subfloors and wall/roof sheathing, CDX is what you'd want.

As to the shower floor, 3/4" CDX ply is fine. If the subfloor were wood planking or 1/2" ply instead of 3/4", I'd add another layer of ply on top to isolate the wood planks from the deck mud or to strengthen the 1/2" CDX, depending on which you have.

So once you have your plywood subfloor in place:

On top of that I put down a "slip sheet". I use 6-mil poly, some use tar paper. Staple it to the floor, just enough staples to tack it into place. If there is any radiant floor heating under the shower, don't use tar paper. Instead use poly.

Over the poly use expanded diamond mesh, that gets nailed to the floor right on top of the poly. Overlap any seams and work to get the mesh flat so there are no "pops" in it when you walk on it.

The deck mud then gets packed on top of the mesh, pack it in well and build it up to the required thickness and slope.

Mongo

As usual, thanks so much! I see you re-posted the fantastic installation demo, too. I actually printed that whole posting, a few months ago.

Hey Bill, if you read this, I occasionally buy plants at Filanowskis, a stone's throw from your old window-shattering-from-the-copters house. I can see why you like Maine better, but I really love Connecticut (except the people are a bit friendlier down in Pennsylvania where I grew up).

I time almost all my travelling to avoid "rush" hour, but if not, I often take back road routes. I'd rather drive 30 mph in peace than stop and go on the highways.

Lainie

I assume that's what used to be Gloria's over by Plains Rd. and Rte. 1?

Well, talk about off topic! (sorry everyone else!!)

No, I think Glorias is still there. Filinowskis was (or is) very close to the Wheelers....Exit off the Merritt. I don't even think they had a sign at the end of the driveway, very low key, more like a wholesaler. But many greenhouses filled with plants and very low prices.

Gosh, irrelevant now anyway! And I stopped going there cause I cut back on volume of planting in recent years.

Lainie