Is there any guideline on how much of the expansive foam to use? I have a
chimney and where it meets the concrete roof tiles the gap is too large for
caulk or sealant. As a matter of fact I can fit two fingers along one edge
and there is a small crevice under the tiles as well where they meet. Even
though I am pretty sure there is flashing underneath I will still feel
better if I can fill the crevice along the perimeter.

I thought I would use those foam that expands, however last time I used it I
did a poor job of it and underestimated how much to use and it ended up
expanding and cracking the surface I put on top of it. I wonder what is the
best way to gauge how much to apply.

Thanks,

MC