12-20-2011, 08:00 AM
With all the arguing/ discussions going on in the shower/ bathtub forum, I thought it might be best to post a seperate thread in the remodel forum, as my question does not really pertain to showers or bathtub enclosures.On Tavy's website, he shows his Thin skin mat product and the glue for it. Have any tile Pros or DIYers here tried that product and have any personally experienced pros/cons on the product? I just need it to use as a method of setting down porcelain tiles 5"X32" "wood grain" planking on top of the plywood subfloor. My options are Ditra, which is easily available, but specifies unmodified thinset on top of it to bond the tiles, Spider Web, which allows modified thinset under and above it, Noble Seal TS top/bottom modified allowed, Cement board. The Tavy thin skin looks like the easiest to use, but I'm not looking for the easiest way out if the results will be poor. hehe:o
12-20-2011, 09:01 AM
I've used cbu and Ditra. Both have been available for ages and work. Between the two, Ditra is FAR easier to install, carry home, cut, and provides benefits not available in cbu. You either believe the manufacturer or you don't, but they've all been in business for ages, and widespread failures caused by technique would certainly have been found by now.
The thinset on the top of Ditra does NOT bond it to the membrane, it supports the tile vertically and holds the tile to it. As a result, as long as it sticks to the tile, it works, there's no shear mechanism between the thinset/tile and the substrate. It is locked into the membrane by the dovetail feature of the waffles. Spiderweb holds up the tile up in a similar manner, but the pockets/waffles are not dovetail shaped, at least not as described in their literature. With Spiderweb, it holds the tile by the thinset locking itself to welded on fibers. Now, they also state that some of them are designed to shear off in stressful, flexing. So, you now have fewer holding the tile to the membrane. To lock the thinset to and around the small fibers that can flex, a modified is specified/required. The whole thing is engineered so that for either DItra or SpiderWeb, when you follow the instructions, it will work. I like the mechanical lock with the dovetails over the chemical lock to the fibers to hold the tile in place. Either thinset would stick to the tile, but because of the drying issue (and not sure how Spiderweb, being waterproof, with a waterproof (well, porcelain is very close) tile allows the modified thinset to dry so it can achieve the specified strength. Being relatively new (not necessarily a bad thing at all), it doesn't have a huge long-term use history.
You are NOT bonding the tile to the floor on Ditra with the thinset, only bonding it to the tile. It is locked into the DItra with the dovetails. The mat is bonded to the substrate with an appropriate thinset locking the fleece which is attached to the main DItra layer. Both sides have some flex to them with the tile/thinset layers bonded together on top and the fleece locked into the membrane on the bottom. An elegantly designed SYSTEM, made up of parts that should be installed per the system design. Dryset thinset achieves it's stated strength more reliably when cured anerobically (i.e., without air drying) on Ditra because it is between the nearly impervious tile and the waterproof membrane. Dryset thinsets achieve, on average, around 250#/sqin hold. Which do you think will break first, a membrane bond or the tile/thinset bond? Remember, on Ditra, the thinset is only holding onto the tile, it is mechanically locked to the membrane via the dovetails. On Spiderweb, it is relying on being bonded to the fibers. On cbu, it is bonded to the cbu, and the cbu/thinset/tile is held to the floor via the nails/screws and because the concrete/tile tend to expand/contract in similar manners, it is the whole assembly that will debond from the floor. The nails or screws keep it from coming up or moving much laterally...but, the thinset used there is primarily there to fill voids, not hold it down. There's much less tolerance for flex on a cbu install, and a modified thinset holding the tile becomes more important.
With any porcelain tile, to get any thinset to bond really well especially on large format tile, you need to burn in a layer of thinset into the back of it. This is the procedure where you use the flat side of the trowel and push thinset into the pores of the tile. It takes a little practice, but I think it's actually easier with a dryset than a modified. Done right, the bond is tenacious and far stronger than the fleece on Ditra or the fibers on Spiderweb, so then it is more the method the tile is held into/onto the membrane.
If you just set the tile, without burning in a layer on the back, especially on a large format tile, you can't apply enough pressure to ensure you're going to get full coverage or embed it into the pores well. There are some specialty trowels that have leaning notches so there's full coverage of a calibrated quantity of thinset that are neat (the height of the notch is such that it is designed to actually fall over so the floor has a full cover of thinset), but you don't see them in the stores very often. Since thinset sticks to thinset great, once you have a layer on the back of the tile, when you set it down, it is very difficult to remove.
You can choose to belive the industry's testing or an individual, myself included. Poor adherance to the instruction manual can lead to failures. You may hear about failures, but don't hear if the products were installed properly. I had some tires replaced on a vehicle, drove out the door, after a 1/4-mile or so, turned around and came back. They'd not tighten any of the lug bolts! They had to replace them all, all the way around. Do I blame the wheel manufacturer that it wasn't resilient enough to handle improper techinque or the bolts for being soft enough so that the wheel mangled them? I don't think so.
Much ado about nothing.
All of these systems have been tested, some only in the lab and short field use and meet industry standards when installed properly. You make your own choice as an educated consumer. Feel free to make your own educated decision. Discussion is good, distractions aren't. Test results speak for themselves. What's best for you may not be best for me when you take your conditions into account. When manufacturers specify a modified thinset for their product, they generally mean it so that it covers all possible situations. When it comes to Ditra, if you ask, and they understand the SYSTEM, I don't think you'd have any problems.
12-20-2011, 02:46 PM
Although I may not have expressed myself properly in my post, because I have read the spec sheets and instruction manuals for these products, I do have a fairly good idea of the mechanics of these. I have decided to go with the Ditra and used unmodified on top as Schluter wants it, and I will back-butter each tile with the thinset as you and others have been wise to point out to me to ensure that the thinset has bonded well to the bottoms of each tile. I have a piece of Ditra, and I like the way it looks and feels, and I can see the waffles are dovetailed. Looks like a good product to me. I just installed about 800 marble subway tiles on the walls of my bathroom project and back-buttered each and every one of those little 3X6 inch suckers. They are stuck on real good.