I've just got a load of parts back from the shotblasters and was wondering how many coats of silver por15 I'll need to apply (spray or brush).I've used it before on rusty areas underneath where appearance isn't so critical.These parts are going to be seen in the engine bay etc.Once they are done in por15 I will spray them with 2pack paint.I just really need to know the minimum coats needed for the parts to be permanently rust proof (is one enough?).Thanks.

 

One is generally enough....
except for me ...
With parts on a bench or in sunlight I do ok

At night, upside down, on my back (floor pans, wheel wells etc)
I always seem to miss a spot or two and so ended up with
two.

On my fenders and rocker panels ...
I thinned por-15 silver and the por 15 tye coat primer.
I did this because I didn't want to paint the whole car.
Por 15 and its primer are pretty thick. They will build up
the surface rapidly. The build up is so quick that you can
easily get above the surrounding paint before adding
color.

If you use the aluminized high temp stuff for exhaust manifolds
y-pipe, echaust system and such...two coats ... Just do it
be careful upon reassembly as it won't cure below
300 degrees and so is a bit soft until properly heated.
I don't have an oven so I had to wait until I could run
the engine to get these up to temp.

One ambiguity with por 15 stuff is "how clean should it be"
I have had excellent success with the rule of thumb
that if it "flashes over" after rinsing its clean enough
If it doesn't there is still some sort of oil on the piece.

( I am somewhat parsimonious and so probably don't
change out my solvents often enough :-))