Primer Problems

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PostPosted: Wed Oct 10, 2018 5:25 pm
Bought some UPOL 2K Urethane primer; added the right amount of hardener and added lacquer thinner. After the primer dried, started sanding - I'm getting small globs (clogging) in the sandpaper. Contacted seller, and he said I had to use urethane reducer instead of lacquer thinner.

I bought the reducer and sprayed some small areas under the hood - it does seem to be better.

My question is this:
I'm working on a fiberglass Cobra kit car, and am hesitant to sand off all the primer I sprayed that is clogging my sandpaper because I don't want to sand too far into the gelcoat and lose the body lines.

To scuff it I have to sand and then air blow the paint clogs out of the sandpaper so the clogs don't leave marks. It's hard to get the primer smooth.

Is it safe to scuff it and reshoot with the urethane reduced primer or does it have to be stripped ?

Thanks,

Jim

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PostPosted: Wed Oct 10, 2018 7:05 pm
See if you can wipe the primer off with lacquer thinner soaked rag.

Reading the Tech Sheet for all the products you use is really not optional. The only thing I use lacquer thinner for is cleaning my spray guns and cleaning up messes.

I would recommend you purchase some quality epoxy primer and once you get the ruined primer off the car, prep and spray a couple of coats of the epoxy primer. You can then spray your 2k over that without having to sand if you stay in the re-coat window. (Read Tech Sheet)

The epoxy will also give you a reference on your block sanding.
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ACTS 16:31



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PostPosted: Wed Oct 10, 2018 8:58 pm
:goodpost: and yes you really need to get the screwed up primer off. what your not going to like is a paint failure a few months down the road then its going to be twice as hard to fix.
Jay D.
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PostPosted: Wed Oct 10, 2018 11:57 pm
badsix wrote::goodpost: and yes you really need to get the screwed up primer off. what your not going to like is a paint failure a few months down the road then its going to be twice as hard to fix.
Jay D.



Thanks RT and Bad Six.


I hope thinner will remove it, since it's soft it probably will.


Jim

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PostPosted: Thu Oct 11, 2018 8:12 am
If you are using a lacquer thinner from a big box store and it is slow going you might try to upgrade to a "hotter" lacquer thinner. Premium grade wood lacquer thinners are designed for catalytic wood lacquers and are much more aggressive. You should be able to get those at any higher end paint center or wood cabinet supply shop.
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PostPosted: Thu Oct 11, 2018 10:57 am
:goodpost: most people think lacquer thinner is just lacquer thinner. in reality there is a huge difference between economy and premium lacquer.
Jay D.
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PostPosted: Sat Oct 13, 2018 2:06 am
Thanks DarrelK & Badsix,

Haven't tried thinner on the primer yet -- will let you know what happens.

Jim

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PostPosted: Sat Oct 13, 2018 8:59 am
You don't ever use lacquer thinner in 2K urethane primer, ever!
Lacquer thinner is not compatible with urethane or the activator.
You use urethane reducer.
(Read the directions)
JC.

(It's not custom painting-it's custom sanding)

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PostPosted: Sun Oct 14, 2018 10:14 pm
This was my first attempt at using urethane primer. Up to now, I've used regular 2K primer and thinned it using lacquer thinner with no problems.

Since that primer was no longer available, I had to choose another brand -- and chose the Upol . Never realized it couldn't be thinned with small amount of lacquer thinner. (5%)

What a PITA ! The thinner I have won't take the Upol off, and sanding fills the paper up with lumps and leaves an uneven surface. I may try sanding first and then the thinner. If that fails -- my next step is to find hotter primer and see what happens.

I can't use stripper as I've done some fiberglass work on the car and used body filler as a replacement on the gelcoat that was removed to do the work. Stripper would remove the body filler and possibly the gel coat.

I used stripper on a fiberglass boat once, and it cut through the gelcoat and removed the metal flake and left pits that had to be filled. Had to have the entire boat top repaired with new gel coat with flake, and the bottom repainted.


Jim

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PostPosted: Mon Oct 15, 2018 7:56 am
That gummy mess you have on there now needs to come off completely. Maybe use stripper everywhere except where you put the fiberglass on?

If its all fiberglass then sand down as far as possible (plan to use a lot of sandpaper) and then shoot two coats of a quality epoxy primer and let it set for 24 hours. At that point you can try spraying some "properly mixed" 2k over the epoxy.

Again the Tech Sheet for your products must be read and followed. Never trust a salesman to steer you straight on something as critical and expensive as this.

Use lacquer thinner ONLY for cleaning up tools after painting. Never to wipe a car down or mix into today's urethane based paints, primers or clears.
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