Originally Posted by TomServo
I've been working on tiling my kitchen floor over the past few weeks (yes, weeks...I know).
I'm using Ditra underlayment from Schluter and had been following the instructions to the letter, which led me to acquire some CustomBlend thinset mortar, made by Custom Building Products. Schluter recommends an unmodified thinset to use between Ditra and the tile. Unfortunately, I had no sense that the only unmodified thinset available at Home Depot would be such as subpar product, as I have read since using it.
So, here's my situation. I mixed up a 50-lb. bag of CustomBlend last night and used it to put down about 50 of my 12x12" porcelain tiles. This morning I googled the product name to check for advice on curing time and I came to find out that most people who work with tile would suggest that you avoid this product like the plague. Also, I've learned that unmodified thinsets just don't bond very well to porcelain. Apparently, many people use modified thinset on top of Ditra with good success, typically something like Versabond with low additive content. You'd void the warranty from Schluter in the process, but at least you're using something higher quality (generally speaking...there are better unmodified thinsets) that's more likely to bond well.
Anyway, I hate the thought that I may have undermined my tile installation with this single bad choice, but what I am to do about it now? Should I actually rip out this tile and do it over? Or is that more hassle than its worth? What is the likelihood that the CustomBlend might actually fail in some way?
Sorry I couldn't be of any help sooner but I just stumbled on your thread and wanted to set the record straight.
1) You DONOT use Un-Modified thinset to bond any type of tile and stone underlayment (i.e. Schleuter Ditra or Cement/Fiber Board) to your plywood/concrete unless the underlayment manufacture requires you to do so, which I haven't come across.
2) I would never recommend a sub-par product. Custom is not a bad product but if you look at it's specs, neither is it great. Example: Laticrete 255 MultiMax or Laticrete Platinum carry a Lifetime warranty when installed per manufacture requirements. Laticrete will repair any damage as a result of the failure of there product.
3) If an installer/contractor is telling you it's OK to use Custom, which most homeowners can buy at there local hardware store, it demonstrates the Level of Quality and commitment to customers long term satisfaction.
4) Never bond unmodified thinset directly to Porcelain. Most Porcelains are either Semi-Vitreous or Vitreous. Simply terms, Water absorption is almost none. You use a Unmodified thinset to adhere to Porcelain, when the water vaporizes you're left with only mortar adhering to a tile with very little porosity. Always use a Modified thinset such as Laticrete 253 Gold or Higher with Porcelain. In the case of using a Ditra system which requires the use of an unmodified thinset between the tile and ditra mat, simply pre-butter all your porcelain tiles with a modified thinset, allow to dry, than install with a unmodified. Dont' forget to backbutter your pre-buttered tiles wells to get good bond between the modified and unmodified thinset.