Should Primer be 'Smooth as Glass' Before Topcoat?

[MrBuick]

As the the title says, I'm wondering how smooth the Primer coat should be before applying the top coat...I've heard varying opinions on this, from people who just prime and paint to people who spend as long buffing/perfecting the primer before they paint...just wanting to hear some opinions. The primer I shoot goes on pretty smoothly and doesn't really have a noticeable orange-peel, but does have a slightly rough feel (like fine-grit sandpaper). I've also seen someone suggesting using comet and a toothbrush rather than sandpaper...just looking for some opinions and tips to get the best final finish. I don't know how well you can tell from the photo...this is a primed hood otherwise untouched...just trying to give you an idea of how it looks before doing any possibly necessary prep work.

[Ace-Garageguy]

For most paints, primer needs to be pretty damm nice to get the best possible topcoat. On REAL cars, we sand it to at least 400 grit before shooting color...600 grit or above if it's going to get a fine-grained pearl, etc.

You DON'T need or want to go really slick though. It's unnecessary and accomplishes nothing. For the VERY FINEST pearls, or buffing metalizers, 1500 grit is as far as you need to go.

If you have no orange peel, then don't sweat sanding it too much. Orange peel will telegraph right through the topcoats. Paint doesn't magically fill surface irregularities, no matter what you may hear.

If your primer is peel-free, I still recommend a thorough scuffing with Comet, etc. This will knock off the slight grittiess you feel, and make a nice, even tooth for the paint to adhere to.

 

Edited February 29, 2016 by Ace-Garageguy

[MrBuick]

Do you mix the Comet with water or just use the dry powder? Doesn't it have bleach? That won't harm anything?

[Ace-Garageguy]

Comet, hot water, old toothbrush. I make a paste in a little cup, dipping into it frequently to get fresh material, as Comet loses its abrasiveness pretty quickly. Not all abrasive cleansers have bleach in them. The Comet product I've been using hasn't caused any problems so far...about 6 years.

I also recommend a final wipe with 70% isopropyl alcohol just prior to painting...especially if your model has sat around for a while. It's a good insurance against fisheyes caused by surface contamination...which I HAVE had happen to models that have been sitting, after primer, for a week or so.

PS: There are gonna be almost as many opinions as there are answers, and lots of different techniques work for different guys. My answers only reflect what works for ME, every time.

Edited February 29, 2016 by Ace-Garageguy

[Snake45]

Every paint job is a law unto itself. Depends on the primer, depends on the final paint, depends on the final finish you want to achieve, and so forth.

That said, I've found that a primer smoothing with 3M #800 WetorDry, used wet, makes just about a perfect base coat for almost anything. #800 isn't easy to find but it's worth the effort--not too much, not too little, "just right!"

[peteski]

The Tamiya fine surface primers I use go on smooth enough not to have to so anything to them to make them ready for the color coat.