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Top coat over 2k time frame

Timw

New Member
#1
How long of a window do I have after sanding 2k regular build with 400 before I seal with reduced epoxy? It's not possible to get all of my parts ready in one day, probably going to take me 3 days to get everything blocked and cleaned. I've heard that I only have a 24 hour window before I'd have to rescuff, but others have said 3 days would be ok. Thanks for your help.
 

Barry

Paint Fanatic
Staff member
#2
Sealing with epoxy just threw the 24 hour resand time out the door, the resand is when going to paint.

Your good to go.
 
#4
I have a couple related novice questions.

1. What goes wrong if 2k doesn’t flash enough between coats? Shrinkage? Adhesion? Bubbles?
2. How do I know if 3 to 5 minutes isn’t enough? Should it all be flat looking? (Not wet?).
3. How long is too long between coats? Can I wait an hour?
 

Barry

Paint Fanatic
Staff member
#5
I have a couple related novice questions.

1. What goes wrong if 2k doesn’t flash enough between coats? Shrinkage? Adhesion? Bubbles?
2. How do I know if 3 to 5 minutes isn’t enough? Should it all be flat looking? (Not wet?).
3. How long is too long between coats? Can I wait an hour?
3 to 5 mins is overkill for my 2ks, 30 to 60 mins would of course work but you would be cleaning between coats and not sure you would gain anything.
Trapped solvents in primer can of course cause fuzzing or shrinkage down the road.
 
#6
I have a couple related novice questions.

1. What goes wrong if 2k doesn’t flash enough between coats? Shrinkage? Adhesion? Bubbles?
2. How do I know if 3 to 5 minutes isn’t enough? Should it all be flat looking? (Not wet?).
3. How long is too long between coats? Can I wait an hour?
I have never had any problems with SPI 2k but prior to that I applied 3 coats of another brand and didn't wait for sufficient flash times.
This resulted in trapped solvents that blistered and cracked in some places, plus excessive shrinkage in others.
If you look at a coat while flashing you will see the vapors escaping and a somewhat wet look in places. It is best to follow the tech sheet and consider the flash times listed as minimums.
The tech sheet will usually give you a time frame for when sanding will be necessary before re-coating.
 

elwood

Registered Users
#7
3 to 5 mins is overkill for my 2ks, 30 to 60 mins would of course work but you would be cleaning between coats and not sure you would gain anything.
Trapped solvents in primer can of course cause fuzzing or shrinkage down the road.
Just wondering, would that fuzzing show up in the clear after being buffed and a year or two has gone by? Looked at a car last year where on top of both front fenders it had a fuzzy look in couple of spots. Had to look closely but it was there. Owner hadn't been able to find anyone who could tell him why it was there. I also had no answer. Painter used PPG all way thru and even PPG jobber didn't have answer. I know this painters work and he had been painting since 1970s. Guy does super, super nice work, and very knowledgeable. The car is super nice everywhere else and you have to really look for this fuzziness. This painter has always had cars at world of wheels for years and years, so I was without an answer. The painter has since retired and moved away. Just wondering.
 
#9
Is it normal to have a solvent smell when sanding 2k? I dont remember as its been awhile since I sanded inside. My particular case was 2k reg build, about 77 degrees in the shop when sprayed, 2 coats, over 5 min and probably closer to 10 between coats, it was visible that it had flashed, sat for about a week before I sanded. Everything seems normal but the smell, seemed to only be on the initial cut.

I wouldn't think it would be an issue, kind of reminds me of the way clear smells when you open it up.
 

Barry

Paint Fanatic
Staff member
#10
Just wondering, would that fuzzing show up in the clear after being buffed and a year or two has gone by? Looked at a car last year where on top of both front fenders it had a fuzzy look in couple of spots. Had to look closely but it was there. Owner hadn't been able to find anyone who could tell him why it was there. I also had no answer. Painter used PPG all way thru and even PPG jobber didn't have answer. I know this painters work and he had been painting since 1970s. Guy does super, super nice work, and very knowledgeable. The car is super nice everywhere else and you have to really look for this fuzziness. This painter has always had cars at world of wheels for years and years, so I was without an answer. The painter has since retired and moved away. Just wondering.
After that long of time for the fuzz to show up, very good chance it was the primer.
But with time frame don't overlook an acid etch primer was used or old lacquer painted over.
 

Barry

Paint Fanatic
Staff member
#11
Is it normal to have a solvent smell when sanding 2k? I dont remember as its been awhile since I sanded inside. My particular case was 2k reg build, about 77 degrees in the shop when sprayed, 2 coats, over 5 min and probably closer to 10 between coats, it was visible that it had flashed, sat for about a week before I sanded. Everything seems normal but the smell, seemed to only be on the initial cut.

I wouldn't think it would be an issue, kind of reminds me of the way clear smells when you open it up.
With all 3 of my primers they cant do that.
I'm not speaking for other primers as some do and some don't.
Depends whats in the 2k.
 
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#13
3 to 5 mins is overkill for my 2ks, 30 to 60 mins would of course work but you would be cleaning between coats and not sure you would gain anything.
Trapped solvents in primer can of course cause fuzzing or shrinkage down the road.
Thanks Barry (and others). I sprayed my hood on Friday and I want to make sure it’s OK. It was my second time using 2k primer, so my spraying wasn’t the best.

I sprayed a coat and waited 5 minutes. It was about half flat and half still wet looking. I waited a little more and decided to put another coat on before the primer thickened too much to spray. I wish I had just dumped the primer. When I sprayed my doors a few months ago, i waited too long and couldn’t shoot a second coat.

Bottom line on the hood, the 2nd coat went on top of some spots that were still wet looking. Each coat was around 4 ounces if that helps. I lightly blocked with 220 a bit after about 4 hours, and finished blocking on Saturday. Most of the 2k has been sanded off, but a few low spots are untouched (low). Will the solvents all evaporate from those spots if it sits long enough?

A few more mills will fill those spots. Being paranoid, I’m tempted to sand those spots back to the epoxy and put some glaze in there rather than have 4 or 5 coats if 2k primer with possible trapped solvents. Thoughts?
 
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Barry

Paint Fanatic
Staff member
#14
Sorry guys but i just looked at my post this morning and used the word can instead of cant.
Sorry, i do try not to post from cell phone but did anyway
 
#15
Hmm I wonder where I went wrong or why I got that smell. I only had it on 1 spot in particular, I wonder if I doubled up or put it on heavy and locked some in, is it possible in a case like that?

I left them sanded in 180 over night and did my finish sanding this morning and then sealed with reduced epoxy and then base coat. Planning on clearing tomorrow. I think it will be alright, but Im not super confident in saying that.
 
#16
Hmm I wonder where I went wrong or why I got that smell. I only had it on 1 spot in particular, I wonder if I doubled up or put it on heavy and locked some in, is it possible in a case like that?

I left them sanded in 180 over night and did my finish sanding this morning and then sealed with reduced epoxy and then base coat. Planning on clearing tomorrow. I think it will be alright, but Im not super confident in saying that.
If I get close, I can smell solvents I start sanding on mine after 2 days. Lets hope it is good.
 

Barry

Paint Fanatic
Staff member
#17
If I get close, I can smell solvents I start sanding on mine after 2 days. Lets hope it is good.
That does not really concern me if after you do break the top layer all solvent smell is gone in say 10 minutes.
Clears can do same thing.
My big concern would be seeing primer fuzz in 3- 6 month if we know everything else under it is perfect.
Not that the fuzzing can't just be buffed out but is there enough cause for a chance at DE-lamination in that spot, down the road.
Buy the way fuzzing is cause by type of talc used and size, mostly a problem with private label primers as buyer is too stupid to know what to request or demand and the maker is trying to add to bottom line.
This is why we replace some of the big talc with Nanos (air filled beads made out of different materials)
 
#18
I just cut into some 2k that I sprayed 7 months ago. I know it wasn’t too thick and that it flashed plenty long between coats. Smelled the same when i cut into it. I’m not worried about it.
 
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