Hi - It's been a year and I haven't done anything in the basement until last week, when I jackhammered up the wet spot in the floor. It turns out that there was more concrete there than I thought. Here's what I saw - wet clay soil below about a 3 mil sheet of plastic, followed by about 3 inches of concrete, topped off by a 1/2" layer of cement which wasn't bonded well with the concrete. After a few days, I now have about a 1/2" of water in the bottom of the hole. There are a couple of things that I don't understand. First, the basement has a working perimeter drain surrounding the hole. The water level in the hole is above level of the perimeter drain. The drain actually only covers three side, even the the hole is well inside the 'U' formed by the drain. What's going on? Is water traveling into the open 'U', or is it coming up from underneath? Second, I have a gravity drain that is dug about a foot and a half below the floor, and drains out back. There is no water in that hole, even though it is well below the one I jackhammered last week. The two holes are about 30' apart. Does this mean that the water in th hole from last week is not due to the water table? It seems like it would be easier for the water to use the gravity drain - it's lower, and the basement floor at that point is also lower. What's going on? Finally, how should I resolve this? Is it OK to have water directly under the floor like that? I was planning on just sealing it up with hydraulic cement, and putting down a floor (using a product designed for damp floors). Is this sufficient or should I do something else? Chris

What do you think, is Ditra worth the money? It's a good product but there is much better preforming options with less thin-set restrictions. Why not prepare the floors with Ardex 8+9? The cost is lower and Ardex 8+9 is also rated as a crack isolation membrane where Ditra is not. Ardex 8+9 is waterproof as well without all the banding work Ditra requires. ARDEX 8+9: Concrete sub floor This is the first coat of Ardex 8+9 over a concrete sunroom floor here in Vancouver. Crack isolation membranes should measure three times the length of the tile. Most crack isolation membranes are between 3'-6'. Since this room will get a 3' wide tile I needed one huge sheet. This is where the cementious memebrane from Ardex excels. I also like that there is no voids under the membrane for little silver fish bugs to crawl around in and make homes. I find silver fish a problem in many Vancouver high rise condo's and try and stop them from making new homes on my projects. Does your answer change if we install slate rather than porcelain? All the more reason to use Ardex or NobleSeal CIS. Both those tile choices will want to see a modified thin-set used.

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!

The highest rated via Robinson test Crack isolation/uncoupler membrane is still Nobleseal TS and CIS if you have an issue with elevation and other membranes are to thick look at Noble. As CTEC stated Ditra is almost always my last choice for multiple reasons .