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Old 06-04-2018, 06:20 PM   #1
mike1954
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Urethane Primer

I have been using urethane primer for the last 2 years on a 56 Chev Truck project. I am down to rear fenders, steps and tailgate.
I have hated this primer from day one. I am sure I am doing something wrong. Mix as directed. I have even started adding some urethane reducer.
Went from 40psi to 30 psi, Opened the gun up some. Did about every thing that I could find on the internet.
I still comes out really rough requiring way to much sanding.
I used lacquer primer 20+ years ago and it supposedly will cause problems down the road.
I have bbw bbc fleetside 64 for my next project and I am considering going back to lacquer primer, how bad would that be?
Just shot some urethane on the rear fenders same old story.

Mike
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Old 06-04-2018, 07:10 PM   #2
72HuggerK20
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Re: Urethane Primer

Make sure your viscosity is right. Follow all mixing directions to the letter, except for reducer. That varies depending on your gun setup, temperature, humidity, etc. I usually look for it to take 1-1.5 seconds for the stream of paint running off your stirring stick to turn to droplets when mixing primer. Maybe try switching products brands.

I'd say not to go to lacquer. To prove my point, go get some lacquer, spray it on one junk panel, then spray urethane on another panel. Then go get some of the reducer you'll be using in your paint, wet a rag down with it, and wipe it over your primed panels. I'll bet the lacquer wipes right off, and the urethane will stay untouched.

Also, explain your sanding process. Urethane primers are meant to be sanded with fairly coarse sandpaper (start with 320), then stepped up to about 600-800 grit, then sealed. They are porous and will suck up basecoat pretty badly if not sealed first.
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Old 06-04-2018, 09:46 PM   #3
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Re: Urethane Primer

Hugger has some great advice!
I would add that a high quality urethane reducer will perform better than cheap urethane reducer. Is your primer of good quality or bottom shelf stuff...with paint products, there is no such thing as good, cheap paint.
Allow proper flash times, use a good primer gun with proper tip size, not an old paint gun and you should have a very nice smooth finish.
Here is what you can expect with proper equipment and proper mix with a high end gun and primer.
You do get what you pay for.
Going to lacquer primer will be a huge mistake.
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Old 06-04-2018, 10:06 PM   #4
mike1954
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Re: Urethane Primer

As for the sanding I have to start with 120 grit every time to get it knocked down then 320, 400 and so on.
it is very hard. I would love start with 220 or 320.
Mine never looks like the bed sides in the picture .
I think I will try a better brand.

Last edited by mike1954; 06-04-2018 at 10:12 PM.
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Old 06-04-2018, 10:43 PM   #5
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Re: Urethane Primer

Mike,
Please tell us the brand and product names of the primer, reduce, gun and sand paper.
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Old 06-05-2018, 11:35 AM   #6
mike1954
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Re: Urethane Primer

I am using the following
Masterpro 8443 2K urethane Primer
Masterpro 5675 Medium urethane reducer
Husky siphon gun with 1.8 tip
Sandpaper Indasa, Norton & GB
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Old 06-05-2018, 01:24 PM   #7
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Re: Urethane Primer

Quote:
Originally Posted by 72HuggerK20 View Post
Make sure your viscosity is right. Follow all mixing directions to the letter, except for reducer. That varies depending on your gun setup, temperature, humidity, etc. I usually look for it to take 1-1.5 seconds for the stream of paint running off your stirring stick to turn to droplets when mixing primer. Maybe try switching products brands.

I'd say not to go to lacquer. To prove my point, go get some lacquer, spray it on one junk panel, then spray urethane on another panel. Then go get some of the reducer you'll be using in your paint, wet a rag down with it, and wipe it over your primed panels. I'll bet the lacquer wipes right off, and the urethane will stay untouched.

Also, explain your sanding process. Urethane primers are meant to be sanded with fairly coarse sandpaper (start with 320), then stepped up to about 600-800 grit, then sealed. They are porous and will suck up basecoat pretty badly if not sealed first.
That really depends on the product. I have primed and painted many, my Gran Sport for instance, I don't have a photo right now. But it was painted right over the tinted urethane primer that was sanded with 600. No die back or shrinkage or anything.

Brian
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Old 06-05-2018, 02:53 PM   #8
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Re: Urethane Primer

I'm no expert but I had issues with the primer I bought.

I decided to swap brands and the problem went away.
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Old 06-05-2018, 10:32 PM   #9
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Re: Urethane Primer

Quote:
Originally Posted by mike1954 View Post
I am using the following
Masterpro 8443 2K urethane Primer
Masterpro 5675 Medium urethane reducer
Husky siphon gun with 1.8 tip
Sandpaper Indasa, Norton & GB
Don't know that brand but can say many private brands are pretty good...but not all.

Like someone else suggested, try a different brand because everything else you are doing seems correct.

Changing to a different brand of urethane primer is a far safer bet than going back to the 80's with lacquer primer!
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Old 06-06-2018, 06:12 PM   #10
sevt_chevelle
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Re: Urethane Primer

Hmmm, most sealers are urethane based, so how does an urethane based sealer prevent an urethane based primer from sucking up all the solvents?
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