>Can anyone compare/contrast the urethane primers such as PPG K-36 or
Dupont 1101S to WLS as to ease of use, sandability, durability, cost,
etc?


I have used WLS and 1101S, but now am using Martin Senour 5190.

1101S is too soft.  It's easy to sand but I worry about the paint
chipping with this soft primer beneath.

5190 is much harder, similar to WLS, I would say.  It is cheaper, and
there is no hazmat shipping fee since I get it at the local NAPA.

I mix in 1% hardner by weight and thin with 5% acetone...all done with
the digital scale. 5190 is a high build, high solids primer so, even
when thinned,  heavy (10 mil) coats dont run.

I only use the primer when I have the micro lapped to about plus or
minus 0.005" measured using
a 24" steel straight edge. After the primer cures I wet sand with 320
grit paper wraped around a paint stir stick. I find it very hard to
correct 5 mil surface errors with micro.  I just cant seem to get
enough where I want it.  But with the primer I just lay a heavier coat
where I want to build up.
The primer is much denser than micro, but a 5 to 10 mil layer all over
the plane will add very little weight.

The blank gray of the primer helps me see the surface shape rather than the
color variations of the micro/fiberglass.

 

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Jeff Peterson N273CK LNC2