75 percent pattern overlap is the sweet spot with self-etch primer. A
second coat is OK, but it is seldom needed, because the self etch must be
top-coated with another primer or sealer before applying paint. The
main goal with self-etch is to get great adhesion to bare metal. Self-etch
will even stick to stainless-steel, but the surface must first be sanded
with 180-grit paper. Because of its acidic nature, self-etch does not work
well with body filler. If there’s going to be a lot of filler involved, use
epoxy instead of self-etch.
After the self-etch is applied, give it about an hour to set at 77 degrees
F before spraying it over with 2K urethane primer. There are many
brands of 2k urethane on the market, and they are available in many
colors with gray, white, black and yellow being the most common. The
2k urethane primers are thick and should be sprayed with a paint gun
that has a 2.0 or larger tip size. With smaller tips, it becomes necessary
to thin the primer with urethane-grade reducer to get it to flow out well,
and then it requires more coats to get a satisfactory build. When using
reducer in primer, it’s best to use a slower reducer than a fast reducer.
This keeps the primer from drying in the air before it hits the surface as
dry-spray primer kills adhesion.
When using 2k urethane primers, two to three coats often gives plenty
of build for sanding and blocking. All 2K urethane primers will need to
be sanded before top coating for a slick surface. The 2K urethanes are
body-filler friendly and sand easily, giving a smooth surface for top
coating. High-build primers can require longer flash times between
coats. Technical data sheets will give the recommendations for each
particular brand of primer. Once the 2k urethane has dried, it can be
sanded and blocked. To get a good finish with high-build primer, it is
common to spray more than once. It is also necessary to repeat the
prime, sand and block process until the surface is smooth. When body
fillers are involved, it can mean more sanding and blocking to hide the
areas that have filler.
One quick note on filler — modern body fillers are remarkable
products that can do almost anything. Don’t be afraid of using filler
where it’s needed. Between good filler and good primer, the surface can
be mirror-smooth with enough effort.
High-build 2K urethane primers shine when used on fiberglass parts. It
is hard to get fiberglass looking good, but high-build is the best bet. Be
singke
(singke)
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