: Thanks Paul,

: So my understanding is that the urethane (or other coating) seals
: the seams, so that they don't leak? Would a standard exterior
: polyurethane work with enough coats? Would a waterbased exterior
: poly work, or should i stick to oils and oil alkyds?

: John R

Seals the seams and ( more importantly ) the weave of the cloth. The needle will make some large-ish holes, but the paint will fill them. If they are too large, let a bit of paint go semi-dry and then use it to seal the holes.

Stick with oil based - not water based. I've never used the water based, but I've heard stories...

BTW, sorry for my links. They should have been:

http://www.youtube.com/watch?v=gYyvIExWkqU

http://www.youtube.com/watch?v=FYWJANqRUsc&feature=related