tips for spraying primer

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mshred

mshred

The Green Manalishi
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Hey guys,

im just about ready to spray my car in high build primer (rolled it on twice already but for some reason i got alot of solvent pop...i think it could be the cold weather here right now in Canada) but just wanted to know any tips you guys may have....the car will be totally blocked in 255, and im going to need atleast 2-3 good coats to cover all the pitting from the solvent pop.

how much primer would i need to do the whole car this many times? what psi should i be spraying at? how much drying time in between coats (this will be painted in either my garage or a school shop in cold weather)? what grit can i block with after spraying the primer, keeping in mind the grit i finished with and the fact that its high build primer?

If you guys could answer these questions or have any other tips or things that are important that you can think of, please drop a line8)

thanks
Matthew
 
You can ask for a faster solvent and slower hardener and try to increase the air flow across the surface. When you spary primer over solvent pop, it may not want to fill the holes, you can use the tip of your finger to rub them / fill them in. You are not that cold in Markam.... yet. It is suppose to get colder later next week.
 
If your spraying the whole car, did you take it all the way down to the metal?. I usually go through about 2-2 1/2 gallons of urethane primer, but i like to block it alot to make sure i have a flat and smooth surface. The air pressur depends, are you using a hvlp gun or a hvhp gun(regular suction gun). For the Gravity type i use about 20 psi-1.7mm tip, but you need to see what your gun requires. When I block I use 180 grit for the first and work my way to 400-600. When you are confident in you work, put a guide coat, or you can use some black spray paint and mist the panels, then wet sand it with 600 and look for any low spots where the black paint is still showing. If you got metal shining your high. You can use guide for any step of blocking you want. Personally i wont prime or paint nothing under 60-65 deg F. Causes a tendency for the paint to want to run and that sucks. Good luck.
 
I would by at least a gallon. Spray a few coats on with a 1.8mm or 2.0mm tip.
Block it with a long hard block and some 180 grit.

Run a tape line down the body lines and block to it, Then switch the tape line over to the other side of the body line and block up to it. This will keep you from hitting the body lines so they come out nice and sharp. If you have a hard time seeing the body lines you can draw them on with a long straight edge and pencil.Then when you8 done blocking scuff the lines with a red scotch brite. That will take the pencil off and knock a bit of the sharpness off the edge.

If it still needs a bit work after the 180 you can re prime and re block with 180 a second time. If its looking good re rime block with 320, then 600 wet.

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hey guys,

the main reason im going to be spraying the high build again is to cover up the solvent pop....the car is straight as ive already primed and blocked it twice now...just need to apply primer again to fill in all the solvent pop (most of which is much less than 1/8th of an inch deep....all the deep stuff will be skimmed with putty)....will spraying the hig build on in a couple of coats do the trick for me? after i sprayed it i planned on blocking with 255 on longboards and guidecoat, then moving somewhere between 400-600 wet... the temperature in markham is about a high of 13 degrees celcius ( i know most of you are in fahrenheit...i dont know the formula to convert it)....should that temperature be okay to spray at? and how much time should i let for drying between coats?
 
If you have solvent pop that deep, you should continue sanding with 180 grit, not try to fill those holes with more high build primer. At 13C, approx 55F, if you're spraying in an unheated shop, wait at least a half hour between coats of high build.
What brand of high build are you using for the job? If you check the data sheets for your particular product, they will give the recoat times and gun pressure settings that work best with their particular product.
Also, if you haven't sprayed high build urethane before, don't mix more than a gun cup full at a time, and blow some gun wash through your gun between re-loads, just to be on the safe side. Good luck.
 
Is solvent pop a common issue? What is the best way to avoid?

Thanks,
 
Solvent pop in primer isn't normally a major problem. You encounter it a lot more in color and clear coats. The major reasons for solvent pop is laying the material on too thick, then not allowing enough time before spraying on subsequent coats. If the solvents in the first coat don't have time to evaporate, then you lay on a second coat, the solvents from the original coat will burst out through the second coat, hense the name 'solvent pop'. You now have small craters at each place the solvents burst through.
Spraying in cooler temps means you should allow more time between coats, since it takes longer for the solvents to escape as the temps drop.
 
hey old vart,

i was planning on swiping the deeper areas with putty (thats what a body guy told me) and then the spraying high build and hopefully filling in the rest of the solvent pop (most of the solvent pop is only visible because of the guidecoat i have on, and when i run my hand over it i cant really even feel the pitting- only slightly in some spots)....Is there anything i should take into consideration when spraying over solvent pop? this is the second time it has happened to me, which is why in now going to spray the primer on instead of rolling it on...is there anything else i should know because i dont want to waste my time spraying primer and then having the pits come through again

thanks guys
Matthew
 
Matthew, do you have a picture of your car as of right now, so I can see exactly where you are with your bodywork/primer? I'm more interested in if you've sanded through to metal in any areas, than in seeing the pinholing itself. The whole idea of high build primer is to build up thickness so you can sand off the high areas and reveal the low areas. Your pinholes are low areas, and if not properly handled, they WILL come back to haunt you down the road.
What high build primer are you using?
 
im using U Pol high build primer....what i have done to try to minimize the deepness of the pinholes is to block each panel with 255 until i start to have the paint underneath or bare metal showing through, then i stop...im doing this to as i said minimize the deepness of al the pinholes...before i reprime i will spray some self etch on the areas now exposed as metal...unfortunatly i dont really have any good pictures of the car right now showing its current state....ill try to take some tonight maybe and post them up...isnt the whole purpose of high build to fill in low spots and imperfections? thats what im assuming the pitting is, an imperfection, and that the high build will fill it...or am i wrong?
 
Do you have any wd-40 in the painting room and or something that has been sprayed with or on lately,:-k I would sand or block any areas that need attention and
scuff it down and prep whip the car down to get any foreign material that
could be present and do everything OldVart has said about waiting and not
jumping pack on it with another primer coat to soon.:thumbrig:
Heck Some times I scuff between coats if it calls for it.=P~

Keep the help coming PopaVart.:rock:

I was spaying a 58 ranchero and I was in the second coat of red enamel
And the wives opened the door and said good bye and you should have been there :tongue9:There perfume came in while the exhaust fans was going and you could see
little bubbles just on the rear passenger bed side where the door the girls opened. .:angry7:

Prep whip solvent and a tack rag is good to have and well worth the small amount needed.

Keep us updated And hope all goes well.:thumbrig:
 
O.K, that's what I wanted to know. If you've hit bare metal in spots, then it's time to stop sanding and put on another coat or two of high build primer.
What I would do in your situation is check the P-sheet for that U-Pol primer and see what you can use to thin it down a little. Usually you can reduce your primer by about 10%, and in this case that's exactly what I'd do. If you spray it at the recommended mixture, you may get bridging of the primer - ie, it will be thick enough it may just bridge the solvent pop craters instead of filling them. If you thin it about 10% with reducer or Xylene, as per manufacturer's recommendations, it should be thin enough to flow into the craters, not just bridge them. I'll see if I can find the U-Pol P-Sheet to see what they recommend for thinning and at what percentage.

And as Mike said, make sure you don't have any silicone products or things like WD-40 in use in your shop while doing any type of body work. It plays havoc with any and all paint products.
 
hey old vart thanks, you seem to know what you are talking about....i could always get the p-sheet from my paint supplier when i go buy another gallon, but if you could find out i would really appreciate it....so if i do thin out the high build when i spray it, how many coats would i need to cover the entire car so that i fill in the solvent pop and still have enough to sand for the final blocking? and will one gallon be enough for this?

thanks
Matthew
 
I don't know but it seems to me if you put the primer on with a roller which its not really meant to be and had an issue with solvent pop I would be concerned that the rest of the paint may not be properly adhered or that you will get shrinkage or some other condition when the weather warms up. I would be inclined to sand it all off and start over. At the very least get it into a booth where you can bake it for a couple of hours.
 
well the primer was applied with a roller in 25 degree weather (thats canadian degrees celsius) so i think the temperature is fine...i cant be bothered to sand it all back down...would be a waste of product and waste of time for me...the primer is on there and has adhered, just didnt dry properly in between coats
 
Well you can do what you want for sure and it seems like you have already made up your mind. Just don't be surprised next summer if your finished paint job starts to lift or shrinks and you wind up sanding even more material off to start again.
 
I dont understand what you mean by it shrinking still....solvent pop, as far as i understand, is bubbling due to not letting proper dry time between coats....if i have sanded down the primer so that I am actually exposing bare metal in some areas, i would think that i have taken the primer down far enough in order to avoid shrinking....and it has been over a month since the first time i have applied the primer (which was in warm weather) so i cant see how it hasnt dried...yes the best thing would to probably be to start over again, but i dont have the time or space to do that....I have already had a friend who is a bodyman and he even told me that if i swipe putty in the deeper areas and prime over it should be fine...i have been told by a couple of other body guys here as well the same thing....I do agree with what your saying no doubt, but im going to take the hopeful route and less time consuming one as well and hope that everything works out for the better....if anybody else has any tips for spraying primer, please share...also, if anybody has any actual experience with spraying over solvent pop, please share how you did it

thanks
Matthew
 
Matthew, i checked out the U-Pol site and they have several types of Urethane primer, and one polyester primer, and that is ReFace. The urethane primers are 3:1, 4:1, and 5:1, and can all be reduced 10% with 2041 reducer.

So, which one of these primers are you using?
 
Matthew, I am by no means an expert and my knowledge is based on taking a body work course and reading. My concern and I hope someone that knows a lot more than me will jump in and correct me if i am wrong.

You have a window of opportunity for applying consecutive coats of paint, too soon and it runs and two long and you trap solvents. When you wait beyond the window you have to give the first coat a much longer time to completely cure then scuff the surface for a second coat.

My concern was that you used a roller which would put down a much heavier coat and the fact that you got solvent popping through the second coat you may still have solvent trapped in the first coat. Over time that solvent will get out but as it does the remaining paint in the first coat will shrink. This will cause crazing in the coats above and/or cause the coats above to lift.
 
Hey OldVart I am using the 4:1 primer....thanks for looking for me...so if i use this reducer, it should help me out when spraying over the solvent pop? how many coats do you think i would need, and how much would a gallon of high build cover for me? Also dgc333, i applied about 3 coats of high build with a roller a month ago...sanded that down and got solvent pop, so i sanded the primer down to the point where most spots the paint underneath or bare metal was showing through....i then rolled on another 4 coats of high build, giving about one hour of drying time between each in order to fill in the solvent pop and prevent it from happenning again....that was about 2 weeks ago...i have now sanded that application down to where the original paint is showing and i am still getting solvent pop....would this still be a candidate for a problem? OldVart, do you know anything about this at all? I just want to make sure that this next step of me spraying primer isnt going to be a waste again...i want to be sure that i can fix the solvent pop and move on to the final sand, and then paint

thanks so much guys so far
Matthew
 
Matthew, I'm not sure how much of what you're seeing is solvent pop. When you use a roller on something like a 4:1, you're laying on a LOT of material. The nature of a roller would produce air bubbles if you rolling a little too fast, and the thicker the material, the higher propensity for bubbling. If you've sanded most of the high build off, then I don't think you should encounter too many problems.
Dcg333 has a very valid point with the trapped solvents, which is what I explained in one of my original replies. If this was paint, either base, SS, or clear, I'd give you the same advice, sand it all off and start over. The fact that it's urethane primer, that has been mostly sanded off, and has had ample time to off-gas, I would just carry on as you plan.
If you get the 2041 reducer for your 4:1 urethane primer here's what I would do. Mix up enough properly reduced and thinned material to fill your spray gun cup once, and spray the hood and trunk lid. You may get one coat on each or you may get two, but from experience, I'd say you should get one good coat on each panel. Let this dry completely for a day or two, especially if the temps are below about 15C. Then, take your long board, some 180 grit dry sandpaper, and sand GENTLY. In other words, let the sandpaper do the work, don't be pushing on the board to try and get a faster cut. :) During this process, watch for ANY sign of the original craters from your previous primer coats. You know what they look like now, and you'll kow if they get any better or worse after this thinned primer coat. If it looks like the primer is doing the job, do the same with the remainder of the car. If it looks like the original craters are still there - STOP - and go back to where you originally started prior to rolling on the first coar of urethane primer.

Also, the P-sheet for your 4:1 primer calls for a 15 minute recoat window, and a 10 minute recoat window if you use the 2041 thinner @ 10% of mixed product. CAUTION: These times are for ambient temps of about 19C, so, with temps in the 12 - 14C range right now, I'd double those time to be on the safe side. You don't want to trap any more solvents now, do you? :)

Hope this helps, and good luck.
 
Sounds like you have a plan! :)

Not related to your issue but this thread made me think of an incident and chuckle, so I though i would share!!

A buddy of mine purchased a 34 Ford 3 window street rod kit. After a 1 1/2year effort working on building the car he was ready for paint. His initial plan was to have it done by a local shop that does restoration work but it was going to take to long so he decided to do it himself. He has never painted anything before and never even owned a spray gun.

The fiberglass body was pretty straight an didn't need much work so after several coats of high build primer and block sanding he was ready for color.

Off to the local paint supply house for some Hugger Orange base coat. The paint he got was supposed to be mixed 1:1 with reducer so he got a gallon of each. Now this guy is of the mind set that you only read the instructions if all else fails. The guy at the paint supply store told him what to do so he never looked at the containers or read the spec sheet.

The paint store gave him lacquer thinner instead of the correct reducer (apparently the cans had similar looking labels). He sprayed on two coats of this mixture when he relaized it was attacking the primer and it was lifting. When i stopped by the entire body was a mess. He had to wait a couple of days for it dry so it could be sanded. He had to sand it right down to the gel coat and start over.

The paint supply store made good by giving him all the materials to reprime, block sand, base and clear. If he had read either can he would have known they didn't go together.
 
hey oldvart thanks again...one question though- would spraying 1-2 coats of high build be enough to fill in the solvent pop? and if 1-2 coats is enough, would a gallon of the high build be enough to do the whole care properly? I have been sanding gently as i block, so thats nothing new....just praying that i can say bye bye to this solvent pop this time and get the car in paint
 
Dave, that's an all too frequent occurrence when a novice listens to the "paint store guy". :) I still print out a copy of the P-sheet for everything from epoxy primer to clearcoat and have it taped up at my mixing table each time I use the product - and I've still managed to blonde moment a few mixes over the past 40 years. :)

Matthew, without actually seeing the car, I can't really tell you if a coat or two of thinned urethane will fill those solvent pop craters. If all the damage is from solvent pop, then it will be worse on the hood and trunk lid, just because that's where it gets put on thickest, and I imagine that would hold true for a roller as well as a spray gun. If it smooths things out in those two areas, then the remainder of the car should be a cake-walk.

What type of spray gun, and what size nozzle and tip are you using? This could make a huge difference in how your 4:1 primer sprays out also.
 
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