In reassembling the floor around my new hearth, I have to stick a
strip of board on top of the edge of a blockwork sub-hearth. In stock
I have a tube of Evo-Grip solvent based grabby stuff. Obviously I've
used the stuff before, but not in this application. My question is,
should I seal the block in some way before using this, or will it work
better on a porous surface?

Cheers
Richard