Mud bed over self leveling compound
I'll put my question up front and then some background.
Question: Should I use a lathe under a mud bed with topical waterproofing for a plywood+SLC subfloor?
Background: I know SLC is normally not used (or necessary) with mud beds, which is why I'm having trouble finding an answer to my question. I had originally intended to use a Kerdi tray, thus the SLC. I had never used SLC and wasn't prepared for how quickly it set up, so I ended up with a floor that was thicker and still not level. The slope was going west-east and my shower door with perimeter linear drain was going to be on the east end of the north wall if that makes sense. Why that matters is I told myself the slope wouldn't really matter since it would just help direct water toward the side with the drain.
So, I set the pan and drain only to realize that the west to east slope meant my drain wasn't going to be level, since the pan slopes south to north. I was frustrated and moved on with other areas of the remodel while I contemplated what to do with the shower.
A week or two ago I came across Isaac's video on doing a mud bed with a topical waterproofing, and this was the answer to all my problems! I had avoided a traditional mud bed because I couldn't afford the height with a curbless design.
I cut my losses with the Kerdi pan and tore that out ground off the thinset. My new plan is to add 1/2" of plywood and Ditra-Heat in the adjacent areas, which will give me 1.5 inches at the threshold when combined with the recessed shower floor. I'm also switching to a point drain as I've heard that linear drains get nasty quick (my wife and I both have long hair).
I have my new materials lined up and I have watched enough tutorials that I feel comfortable with doing a mud bed. I just can't seem to find an answer on the lathe. I could always grind all of the SLC off, but I feel like it would be better to just leave it so that the thinset under the deck mud has a better surface to adhere to than wood.
Thanks and sorry for the long winded question!
Thanks, Bryan and Isaac! I'll plan to go with a bonded mud bed and skip the lathe. That is good to know regarding the porosity. I'm pretty sure I have some primer leftover that I can use.