Tile Mastic Dries Before Installing Tiles?

Yes, this happens.  What you do is lay down too much mastic in proportion to the number of tiles you can lay in the next column or row.

Us DIY tilers often have “eyes” bigger than our “hands.”  The opposite scenario is laying down just a little bit of mastic, laying down 2 or 3 tiles, laying down more mastic, and doing this over and over.  It gets tiring.  That’s the point where most of us start increasing the amount of mastic.

You will know if the mastic is too dry to install tile when it has “skinned over.”  Skinning over means that the very top of the mastic has develope a thin, dry layer.  To the touch, it may not feel like much.  In fact, you can even break through it with your fingernail.

But don’t do this.  Even that thin skin is enough to prevent your tiles from sticking properly.

Don’t throw skinned-over mastic back in your bucket of mastic, or you’ll ruin the stuff in the bucket.

Carefully scrape off any “skinned over” mastic from the wall and dispose of it.

Then reapply mastic to your wall–less mastic this time around, of course–and start tiling again.