My first thought was that maybe there was dust on the board. So we used a damp rag and wiped it down before as we went...
The problem occured mostly when trying to notch the ridges.
We overcame the problem by mixing it a little more wet than usual....
Originally Posted by Tileworks
I've never used Shaw Multiset, but I am a regular user of Fiberock underlayment. If thinset isn't sticking, usually dust is to blame. Was the board clean?
Always burn the thinset in with the flat side of the trowel and then come back over it and comb your ridges.
Also, your thinset should be a modified thinset, with versabond or equivalent being the bare bones minimum.