Why does it (U-pol) crack when dry sometimes but in other places, doesn't? Is it something to do with the thickness with which it's applied?

thickness and what its being applied to. if it over zinc primer or rattle can it often cracks and looks awful. other times it goes on sweet! its another black art of 2cvism. I used mastic gun seam sealer on the ami with great sucess! (no ali G accent applied)

TIM

Most of mine's over stone chip but some of it's OK, some not. Must be the thickness then. I must admit that I didn't find it the easiest stuff to use.

I'm intending to apply a small amount round my window frames to try and guarantee water-tightness before I fit the windows.

Bertie I used 'brushable' seam sealer which is a laugh really as how-T-F you're supposed to brush something so stiff is beyond me. I finished up applying two parallel strips of masking tape either side of the seam, brushing the stuff on in between them with with a short stubby bristled brush, and then peeling the masking tape off quickly before it sets. Turned out quite neat and hasn't cracked as yet.

If I did it again I might use gaffer tape instead as the masking stuff can rip easily when peeling it off.

Would not warming it up make it more workable to brush.