I have scraped most of the drywall mud off of this joint. I can wash off the rest. There still is drywall mud under the paint. The mud is about 1/8" thick and was used to smooth between the corner pieces. Tile will go up 3-6" above the drywall/durock joint. Is there anything I can cover the mud with? Edwena

Discalimer: I'm clearly no expert . . . It seems to be builders' preference. My tiler was used to doing Durock for commercial applications--stronger, more vandal-proof. I dislike Durock's "crumbly" edges (warranted or not), so I chose Hardibacker instead. It's easy to cut. Unlike Durock, however, Hardi wicks water easily (even though it's "waterproof," it's not vapor-proof, like a Kerdi, Tyvek, or other vapor/water-proof membrane. Hardi just doesn't warp or get damaged by water). That in mind, installed correctly, I'm sure all of the available commercial cementboard products do their job satisfactorily. I did my guest bath in Hardibacker with a Tyvek vapor barrier between the Hardi and the studs. However, in the master bath shower, I really want to do a Kerdi shower. The Kerdi system seems like the best system for no-worry, never-leak membrane systems. The peace of mind will be well worth the $400-$500 in materials cost (which I think is trivial in light of the cost of all the other materials, fixtures, and labor you're about to invest in). Just my novice opinion . . . I'll let the real experts chime in now.

I have been blessed to live in a beautiful island state where the ocean is a key part of our daily lives. But all of you, regardless of address, has a responsibility to the planet. Whether you believe Earth came to us in a big bang or was given to us by a loving creator, it is our choices that will shape it for future generations. 1. The fact that Styrofoam is lightweight and floats, means that over time a great deal of Styrofoam has accumulated along coasts and waterways. It is now considered the main component of marine debris. Styrofoam is manufactured by using HFCs, or hydrofluorocarbons, which have negative impacts on the ozone layer. Styrene is also known to be toxic to the reproductive system. The brominated flame retardants that are used on Styrofoam are also causing concern, and research shows that these chemicals have negative environmental and health effects. Combined with the fact that all the scraps and waste of this Kerdi-Board material will be sitting in landfills for hundreds of years because it takes so long to biodegrade. 2. The laminate (waterproofing) that Kerdi is made from is polyethylene. The same plastic that the grocery bags are made out of. Which are now outlawed in Kauai and Maui counties. There are many ways plastic is bad for our environment. From its manufacture to its disposal, polyethylene emits toxic compounds. During the manufacturing process dioxin and other persistent pollutants are emitted into the air, water and land, which present both acute and chronic health hazards. During use, polyethylene products leach toxic additives. When polyethylene reaches the end of its useful life, it can be either landfilled, where it leaches toxic additives or incinerated, again emitting dioxin. The world's "great garbage patch" can be found floating between Hawaii and San Francisco. This garbage patch is estimated to be twice the size of Texas and thousands of pounds of our discarded trash, mostly plastics. These materials have no business being pumped into our economy and homes. Large corporations make up lies about the impact the production of such materials has on our earth and it's inhabitants. I will have no part in increasing the use of these materials. Not when mortar methods are and have been available to us for generations. It is only laziness that breeds the use of these products. They, in no way, lead to a better finished product.

If you have a 1/4" to 1/2" gap at the tub that needs to be filled, consider installing a veneer of cement board on the walls. That would cover the gap and give you a pristine surface to work off of. The negative to that will be twofold; you'll need to consider the detail at the edge of the tile on the two end walls with regards to hiding the edge of the cement board, and you'll want to make sure your valve trim kit can accommodate the extra thickness of the cement board. The cement board edge can be hidden with a tile trim piece, a return, or with a wood trim boarder that melds with the other trim in the bathroom. The semi-gloss paint on the walls is a big negative for me. Thinset is less likely to develop a bond with it, and because of it's permeability, semi-gloss can create difficulty with modified thinsets drying versus an unmodified curing. With that info given, I'll try to answer your questions: "1) Can I use a lightly modified thinset (versabond) instead of unmodified? (I know this will void the warranty, but will it hold better?" Modified will develop a stronger bond then unmodified in a pristine installation. But you could encounter drying difficulties by sandwiching modified thinset between the semigloss paint on the wall and the kerdi membrane. 2) The plaster wall substrate is not even, particularly where the wall meets the tub, as mentioned. Will this cause a problem when tiling or will the Kerdi membrane help create a flush surface for better tiling? The kerdi will follow the lines of whatever it is installed upon. If the wall is wonky, the kerdi will be wonky. if there are just a few recesses on the wall, they could be built out to the proper plane with applications of thinset or mortar feathered into those areas. Let the thinset or mortar cure, then apply the kerdi. If the recesses are deep and numerous, it might be easier to skin the entire wall with cement board, shimming the board out as needed to get the walls in plane. 3) Should I score the painted wall before applying the thinset to help it adhere better? Yes. Especially with a semi-gloss paint. I'd recommend you go further than that and attack the paint with high-grit sandpaper to really scuff it up, or to even remove it. If you end up with a variety of materials on the wall when you are done (some semi-gloss paint residue, some thinset, some drywall mud, etc) it might make sense to prime the wall in its entirety. Let the primer fully cure, then thinset and Kerdi over the primer. You recognize yours is a messy installation based on your existing substrate. Some plaster. Some semi-gloss. Some drywall mud. Some thinset. Working off a Frankenstein base like that offers no guarantees. That's why my advice, especially considering you have that gap at the tub that needs to be bridged, is to veneer the wall with cement board. Since your walls seem to be a thin plaster veneer over blueboard and not a thick plaster over lathe or a thick multi-coat plaster, you could even strip the walls to the studs. It sounds like a lot of work, but you may very well spend more time trying to make your existing walls right without them ever really being right, versus going to the studs and making them right. Get to the studs. Shim the studs out if needed so the three alcove walls are all in plane. Cement board. Kerdi. Tile. Grout. Done. Shortcuts sometimes take longer than what seems to be the more arduous path. I HIGHLY recommend you contact Schluter tech services. I can somewhat assure you that because of the hybrid nature of your walls, they'll not guarantee you anything. But they can offer you another perspective. Good luck!