Justin -
Saw your questions on the primer/sanding issues. I can't post
replies to
the Forum from work (something to do with the firewall here), so
you might
post up the following response to your questions for people to
see:

First, the 400 grit wet is too course for the final wet sanding
prior to
finish painting. After cure and shrink-back, you will be able
to see
400-grit sanding marks in the finish. 600-grit is the coarsest
grit you can
use without having any problems with seeing any marks. You can
use a little
400 wet to do some rapid cutting down of thick spots in the
primer, but you
need to finish it off with the 600.

On the primer/sealer:
PPG recommends that the DP-series epoxy products be used in two
ways:
DP is used as an epoxy primer/adhesion base right over the bare
substrate
before you start doing any body work/filling/fill priming. On
metal cars,
this provides a sealed surface to prevent any corrosion (fill
primer is
porous, so it does not seal the steel from moisture
penetration). On 'glass
cars, the epoxy prevents any topcoats/primers from reacting with
the
composite underlayers, and creates a stable surface to work off
of. You
then apply the fill-primer (K36 or equivalent) over the top of
the DP. You
must topcoat the DP within 48 hours, or the DP will "seal up"
and you will
not obtain adhesion. If you go past the 48-hour limit, you must
scuff-sand
the DP to break the surface prior to priming over the top of it.

Once you have primed and sanded the car using K36, and you have
guide-coated
it and final sanded with the 600 wet, PPG recommends that the DP
be reduced
as a sealer and shot over the K36 (I can FAX you the PPG
DP-series data
sheet where they define and describe this technique if you'd
like. Your
paint supplier should have the data sheet where it recommends
this
technique). Reduced 25% with DT reducer, the DP becomes a
paint/primer
sealer rather than a primer. This thin coat of epoxy seals up
the porous
K36, and provides an excellent adhesion base for the basecoat.
It also
keeps the basecoat from possibly reacting with anything
underneath, and it
covers up any sand-through spots in the K36. You do not need to
sand the DP
sealer as long as you shoot your basecoat/clearcoat within the
time "window"
for adhesion. However, I find that I like to go over the DP
lightly with a
little 600 wet or a ScotchBrite pad just enough to pull the dust
"nubbers"
out of it and to produce a perfect surface. DP does not sand
well, and will
plug up your sandpaper quickly, so just knock the dust out of it
and then
shoot your basecoat. If you let the DP sit for more than 48
hours, you need
to scuff the entire surface up with ScotchBrite prior to paint.
When wet
sanding prior to paint, use cold water: Use of hot water for
sanding or
rinsing tends to cure and "skim" the surface. Use of cold water
tends to
leave the exposed "pores" in the sealer open for maximum
adhesion.

I have shot several non-show quality cars where I have not
sealed the entire
car with DP prior to basecoat. I have used the DP reduced as a
sealer only
to touch up sand-through spots in the K36, and then shot
basecoat directly
over the K36. I have not had any problems with cars shot like
this. But
PPG recommends the sealer step method in all of their
literature.

Lars Grimsrud