I have had a number of failures related to poor quality setting materials over the past couple decades. In total I think I have had four. All different and with different products from different suppliers.
I learned a valuable lesson from my Schluter rep Bob Weins about 8 years ago I think and had I followed his advice on this current project I would not be behind schedule and out of pocket the time for the repairs. My buddy teased me yesterday that I would not share this info like I do everything else - But he does not know me that well!
I double checked the date code and found that the thin-set was not to old and made May 23 2012. To read the Mapei date code you need to know how they label their bags. The "D" is for Vancouver. "23" is for the 23rd day of the month. "E" is for May (A=Jan, B=Feb, C=Mar....complete code list here). "2" is for 2012 and "51" is the batch or lot number. So this thinset is not even six months old and purchased from a supplier that moves a ton of it. This was the first time this has happen to me with Mapei's products.
Why did it happen?
I'll need to call Mapei on Monday and see if they have any other problems with this lot but I'm assuming they will not. I think what happened here is I grabbed an open bag that I used about five months ago from the shop. I have a memory of doing this and this would explain a lot. If you don't store your setting materials properly and if the bag is left open you can weaken the setting material. I'm pretty sure this is the case but will double check with Mapei that they have no issues with this batch number.
How do you prevent this from happening to you?
The "Idiot Test". About eight years ago I had installed some Kerdi on a project in UBC and the next day we where going to start tiling the walls. I brought down the vacumn and to my horror sucked the Kerdi right off the wall. I called my Schluter rep Bob and asked him what's up and was told that I should check the date code. As it turns out the date code was not on the back so I went hunting for it. I went back to the supplier and sure enough the thin-set was a good 16 months old I think. Thin-set has a shelf life of about 12 months on average. Better thin-set and better bags can last longer but as a rule we like to work with "Fresh Stock" six months old or younger.
The "Idiot Test" was suggested by Bob as a way to test thin-sets. The day before you need to use your product make up a little test. Get two tiles and set them face to face with the setting material you plan to use. If you can pull them apart the next day your thin-set choice is not a good one or your thin-set might be bad.
I'm not impressed that we need to fix up this job but the lesson has been a humbling one and a solid reminder to always test and check the products going into your shower.
In the big picture I'm out few hundred dollars but saved a disaster if we ploughed forward and starting working on top of this faulty layer of Kerabond.
I was joking with my buddy and told him that this step is designed to add microscopic scratches to the wall and floor for better bonding.... LOL He called Bull Shit and he was right.