ir3333
Well-Known Member
are different 2K urethane primers compatible if used long after original coating has cured?
How long do you guys wait to block after priming?
How long do you guys wait to block after priming?
2 K urethane high build
- Thread starter ir3333
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If the first 2k primer has cured then there should be no issue in using a second brand over it.
For sanding I would wait at least 24 hrs after spraying or follow the recommendation of the paint company that made it.
ACME SS
Well-Known Member
Yeah shouldn't be any compatibility issues just follow instructions. After 24 hrs cure i would sand before recoating anything but like@mgoblue9798 said, follow recommendations of the paint company.
Like said always download the tech sheet on any primer/paint. It tells ya how to do it!!
ir3333
Well-Known Member
Local guy i know used to do show quality work and i remember asking him why there was about 3/32" of primer in a clear jar on his bench? He told me when he primes a vehicle he puts that small amount in a jar and when it dries and cracks the car is ready to sand.
That was about 25 years ago!
That was about 25 years ago!
ACME SS
Well-Known Member
That was probably the old lacquer primer surfacer which dried by evaporation rather than curing like a 2K (the 2K means two part as in a hardener). In the early 80's I had a small body shop on our family farm and that is all that we had back then. I would crank out a car every few days and they looked great but then I'd see them from time to time weeks later (sometimes they came back to me for this, other times I just saw them on the street) and the surfacer would have shrunk so much that scratches would show through the paint. I would contact the owner an have to redo the work. About the same time there was a National Geographic documentary on TV where they covered the process of an old Dusenburg or similar car from auction to restoration and the shop that did it waited 30 days between coats of surfacer and the job took 12 months due to waiting on the lacquer to dry like you said. 2K primer is a total game changer.
ir3333
Well-Known Member
OK..that makes sense.
jbc426
Well-Known Member
All of the catalyzed primers shrink over time. Much less so than non-catalyzed primers, but they still shrink. Depending on the finish you are trying to achieve, waiting longer is generally better.
After spraying them out, allow the minimum recommended cure time at the correct recommended temperature and the shrinking is greatly reduced with these products, but there will still be potentially visible shrinkage after 6 months and longer especially if top-coated.
Most 2k that I have used develop a surface that must be sanded for the subsequent top coats to adhere to properly. An added benefit of this surfaces is that it helps block moisture from absorbing through the 2k prime coat over time.
Using the minimum thickness you can get away with will help greatly in minimize this. Using an electronic paint mill gauge can be helpful in guiding your sanding of the surface down to the point before you can see the underlying metal/surface.
^^^ I agree. I have car I did last fall, I see a spot that either shrunk or I did a poor block job on that spot! I used a high build urethane 2K primer. White car but I can see that booger!!
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