2k spi regular primer questions

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hapcj7

Promoted Users
Hi all,
I am new here, and new to auto refinishing. I am currently working on my second bc/cc project, with the first being just 2 bumpers and 2 rocker covers. This project is to repaint a front bumper and car hood, and maybe some blending into the front fenders...I am on a tight budget and looking for a "good/great" repair rather than perfect repair. I am using SPI,s 2k primer and Spi,s production clear..My base coat with be Cromobase k, which is outrageously priced...The reason for the respray is hundreds of rock chips; car is older, high mileage, but clean.. I sanded the OEM finish on my hood down to 220-320 as of now, so the clearcoat is dead flat, no orange peel,,,,,,Did i go too far with my sanding for preparation for proper adhesion for the 2k primer?........I stopped at 180 on the front bumper.......... I will be applying my bc over the sanded and prepped 2k primer. Should i block sand the 2k primer with 400-600,(start and finish with) and thats it, given im happy with what i see, then apply basecoat?...How long can the 2k primer sit for before i need to sand it, before applying basecoat?.. If i need to add additional coats of primer(after perhaps some putty touch ups), how long can primer sit for before i have to sand to add more primer?... If/when sanding is needed, what grit should i use...Thank you in advance
 
I have been in your situation too and here’s how I do that:

Scuffing they original panel so clear is completely dull is fine but your sanding is even better. Then I’d give it a coat or two of epoxy first as a sealer for the original substrate. The next day spray three coats of 2k. For little things like this I rush it and start blocking with 180 or 220 in a few hrs. Use guide coat of course. I think ideal is to sand the following day but I personally have never had any problems sanding after a few hrs. Then you can apply any glazing putties (2k only) over your primer. If everything is happening within a few weeks of each other then I don’t resand again.

Once it’s to your liking, a great trick I was taught by Barry was to spray one medium wet coat of 2k over the entire panel once more and then wet sand it 400 for solid colors or 600 for Metallics. This way there is not need to worry about cancellation of the 220 scratches because they’re filled in.

Note if you’re new to blocking might be better to block with 220 instead of 180 only because it won’t take it off as fast and get you in trouble.

After your final 2k you could go straight to base if it’s uniform color and there are no sand through a, or do a sealer with reduced epoxy. I spray epoxy unreduced and wet sand 600 prior to base.
 
Lizer, all understood, thank you!..If i block out my 1st few coats of 2k primer, what grit sand paper should i stop at to accept final additional coats of 2 k primer?..Or in other words, 2k primer will stick to 80 grit up to what???.. I will final block with 400-600..
 
hapcj7 said:
Lizer, all understood, thank you!..If i block out my 1st few coats of 2k primer, what grit sand paper should i stop at to accept final additional coats of 2 k primer?..Or in other words, 2k primer will stick to 80 grit up to what???.. I will final block with 400-600..
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180-220 grit is just fine. Do not use 80 grit on 2k. You only need one grit for blocking 2k. 180 is common (and faster), 220 gets the job done too, just a little slower which might be better for those just starting out.
 
THanks Lizer!-- I am blocking my final coats of 2 k primer, finally... I am using 400 grit and then was planning to f inish off with 600, both wet... I feel like i need more of a cut..Some of the primer is not sanding dead smooth and flat..Tiny holes would be my best description...I may have been too high on my pressure when i sprayed the 2k,,, The 2k feels dry(ish) and gritty on bumper..If i start with 180 or 220 blocking, can i then go directly to 600?..I doubt it----Thanks again for your time
 
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hapcj7 said:
THanks Lizer!-- I am blocking my final coats of 2 k primer, finally... I am using 400 grit and then was planning to f inish off with 600, both wet... I feel like i need more of a cut..Some of the primer is not sanding dead smooth and flat..Tiny holes would be my best description...I may have been too high on my pressure when i sprayed the 2k,,, The 2k feels dry(ish) and gritty on bumper..If i start with 180 or 220 blocking, can i then go directly to 600?..I doubt it----Thanks again for your time
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Did you do a final coat to fill all your 180 scratches? That is what you’d sand with 400.

It sounds like the primer was spraying too dry, either it needed reducer or was starting to kick or your gun had a plug or small tip.

Any reason you don’t want to go to epoxy next? I sand 2k at final sand as 400 and then do a seal coat of epoxy.

You will want some intermediate grits between 220 and 600, like 400. That’s why like doing a final “fill” coat. Not a lot of build it just fills in scratches and allows you to sand with whatever you want your final grit to be.
 
Hi, Yes, after sanding my previous 2k primer coats with 180, i added some Upol dolphin glaze in several areas.Today, i then applied 3 coats or so over that surface. I attempted to sand with 400, but am not satisfied as stated in previous response. The primer layed down very gritty in some areas. Temp today was 75 ish with about 60% humidity My gun, the only gun i have, is an Lt100 from Eastwood...I sprayed at 25-30 psi, full fluid and about 85 % fan.Tip is 1.7. I mixed the 2k primer normal, 4:1. I bet reducer would have helped me a bunch, or slowing up my speed. Ill see if i have enough primer left on bumper, starting with 220 grit in the "bad" areas, then work with grits as you suggest. The surface may be good enough, but thats where my inexperience comes into play, im not sure what i can get away with. I do know the surface does have some pitting, in areas that were not pitted prior. The 220 may take care of it..Epoxy, yes, i probably should have with gone with that. I am trying to keep this project mostly simple and also on a budget. If i still dont feel the surface is proper, ill do a "fill" coat and add 5 or 10 % reducer. I appreciate your time
 
hapcj7 said:
Hi, Yes, after sanding my previous 2k primer coats with 180, i added some Upol dolphin glaze in several areas.Today, i then applied 3 coats or so over that surface. I attempted to sand with 400, but am not satisfied as stated in previous response. The primer layed down very gritty in some areas. Temp today was 75 ish with about 60% humidity My gun, the only gun i have, is an Lt100 from Eastwood...I sprayed at 25-30 psi, full fluid and about 85 % fan.Tip is 1.7. I mixed the 2k primer normal, 4:1. I bet reducer would have helped me a bunch, or slowing up my speed. Ill see if i have enough primer left on bumper, starting with 220 grit in the "bad" areas, then work with grits as you suggest. The surface may be good enough, but thats where my inexperience comes into play, im not sure what i can get away with. I do know the surface does have some pitting, in areas that were not pitted prior. The 220 may take care of it..Epoxy, yes, i probably should have with gone with that. I am trying to keep this project mostly simple and also on a budget. If i still dont feel the surface is proper, ill do a "fill" coat and add 5 or 10 % reducer. I appreciate your time
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Are you using a guide coat when you’re sanding ? This will inform you as to if your surface is ready or not. Sometimes I’ve got the really rough texture you speak of as well but have never had issues sanding it.
 
Hi there, No, i am not, but Good thinking!!!- Thanks..I thought i could get away on the bumper without it, but maybe not...Ill try it bc i need a guide coat on the hood for sure
 
hapcj7 said:
Hi there, No, i am not, but Good thinking!!!- Thanks..I thought i could get away on the bumper without it, but maybe not...Ill try it bc i need a guide coat on the hood for sure
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If you’re sanding without guidecoat you’re sanding blind and really need it to know once you’ve got everything sufficiently leveled out.

I just use cheap rattle can black spray paint and just put on a very light dusting. It won’t load up sandpaper that way.
 
Hi there, Okayyy, ill do that..I was hesitant to try a rattle can, but i can pick that up any where. Thank you
 
Get Acrylic Lacquer spray paint. Dries a lot faster and won't clog as bad. Just dust it,your not painting it.
What I used before going 3M dry guide. Unless you happen to have some pounce powder laying around.
 
Hi all,
Okay, i think im back on the right track..I looked at the primered surface (bumper)with a magnifying glass and saw alot of pinholes, i guess they are called.My primer sprayed extremely dry....(4:1). I block sanded with 220 and i am mostly happy with my surface now..
My next plan is to spray the same regular 2k primer at 4:1 and reduced about 10%, with a 1.7 tip...... Will this cover the 220 scratches, or should i reblock with 400 wet?... Also, how many coats can i apply or should i apply of the reduced 2k?... After this, i am planning on blocking with 600 wet, hopefully!!...

Humidity- What do we consider to be safe spraying conditions?...Are these numbers the same for primer, base and clears?.... I do not have any retarders

I appreciate your time and help
 
Just apply one coat of the reduced 2k and it should fill in the 220 scratches.



I'm assuming you are doing this but....when you're blocking, you should be removing about 90% of the 2k primer initially applied. You only want the bare minimum on the panel to normalize any low spots or waves. Excessive mil build on a panel is a very bad thing. I will usually guidecoat once more if it's my final block and go again. Chances are you'll still reveal some lower spots that didn't quite get remedied the first pass, even though the guide coat got sanded out.

True story--when I was learning all of this, there was a guy in one of my classes that would go and sand the guide coat out of the low spots.
 
Hi there,
Perfect, thank you. I am not sure how much 2k primer is left after blocking with 220, cant be much though. I am not going for perfection on the bumper, as it has been beat up a touch during its 203K miles, by others. It should turn out nice though..Ill apply 1 coat of the reduced 2k as you suggest, and do the final blocking, hopefully!! Modern bumpers are time consuming to say the least...Should i be able to do my final blocking with 600 wet and only 600, if i get the primer to lay down nicely?...
 
hapcj7 said:
Hi there,
Perfect, thank you. I am not sure how much 2k primer is left after blocking with 220, cant be much though. I am not going for perfection on the bumper, as it has been beat up a touch during its 203K miles, by others. It should turn out nice though..Ill apply 1 coat of the reduced 2k as you suggest, and do the final blocking, hopefully!! Modern bumpers are time consuming to say the least...Should i be able to do my final blocking with 600 wet and only 600, if i get the primer to lay down nicely?...
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Yes you can do that.

I used to paint plastic golf cart bodies. They are usually badly chipped up. For those generally 3 coats 2k would take care of it, then I’d do a final fill coat and wet sand 600 because there was usually a metallic going on next.
 
Thanks again Lizer... I was able to get the reduced, 25%, 2k primer to spray well, yay!..I sprayed some small parts yesterday, bc, cc, and feel they came out fine. The Dupont chromabase seems to match Very well so far. Definately need more time behind the gun.Prep work is critical and needs to be near 100% before doing next step. Bc, and cc is going on the bumper today, then on to prepping the hood and front fenders a bit. Very time consuming. Have a good one
 
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