Primer coats

S

Siciliang35

I'm about close to starting this project which is a bumper. Never done this before.

Does the tech sheet tell you how many coats of primer you should lay on?

Let's say I paint two of the same bumpers everything the same except for the amount of coats of primer I put on.
Will one bumper look lighter or darker than the next if everything else is done identical?
 
'68 Coronet R/T said:
Personally, I would only use epoxy primer on a plastic bumper.
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I will use epoxy primer before I apply base coat as a sealer. That's not what I'm worried about I need to know how many coats 2k Primer I can safely apply without having problems. I'm going to be sanding in between coats checking everything with a dry guide coat to make sure there's no imperfections
 
Keep it as thin as possible. Put 2-3 coats on, then sand most of it off. Most 2K primers are not very flexible, and if you bump the bottom the primer will crack, much like what you have now. Rock chips will also be a problem. That is why '68 suggested epoxy only. It is much more durable against the things front bumpers are subjected to.
 
Ok thank you. Just a double check, after I get all the paint off I finish up with 220, after 220 I'm going to apply adhesion promoter, after the adhesion promoter I will not sand that, I then hit it with the 2K primer. What grit do I finish the 2K primer before the sealer
 
Siciliang35 said:
Ok thank you. Just a double check, after I get all the paint off I finish up with 220, after 220 I'm going to apply adhesion promoter, after the adhesion promoter I will not sand that, I then hit it with the 2K primer. What grit do I finish the 2K primer before the sealer
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You are missing the point we are trying to make - No 2k primer only epoxy primer.
 
I'm doing my research and I'm coming up with different answers. From what I've researched, A 2K primer is sandable ,is ok on a bumper .A epoxy primer Will fill in more than the 2K primer will fill in and it has more adhesion, It will also prevent or help prevent rock chips.

I'm thinking that after I sand the bumper down and get all of the old paint and off, because it's peeling pretty bad. I'm going to have to do some more sanding work to get it even. To avoid filling in with putty too much I was thinking to use a 2K primer like the guy said in here about three coats light and work out the imperfections. Since 2K primer is sandable I figured it will fill in a lot of the sanding marks and some of the imperfections. So after the 2K primer, and sanding, Hit it with the Guide coat to see if I have to sand anymore, and then when I feel like it's smooth enough I can hit it with the extra epoxy primer for the extra adhesion and strength. This is what I've got from all the information I've gathered.

But looking further into it some people say use epoxy before the 2K, some people say use epoxy after the 2K, some people say don't use the 2K at all.
I have nothing but time in my hands right now so I don't mind spending the extra time to do the job the best that I can. This is also a learning experience for me and I'm pretty sure once I get it I got it. So I'm willing to do whatever I have to do to get the end result of a good painted bumper that won't crack under normal circumstances and won't peel at all.I appreciate you guys help just remember I'm new at this and it's hard to grasp unless I actually do it also I'm getting different answers this is why I'm asking questions in here. So if the rule is do not use any 2K primer at all which I've looked up and a lot of people say you can then I won't. If the 2K primer is going to help me with cleaning up the imperfections and it is okay to use then I will use it I just need a definite answer on exactly what to use and why.
 
The best possible job will be epoxy only. As I said above, most 2K is not very flexible or chip resistant, especially as it gets thicker. Epoxy has better flexibility and adhesion. If you have plenty of time, multiple sessions with SPI epoxy would be the ultimate base for color and clear. It is sandable, unlike most epoxies. Final sanding bare plastic with 220 is going to leave a fairly rough surface. A quick wet sand with 320-400 after 220 will leave a surface more easily filled, and would also be a good time to thoroughly wash both sides with Dawn and water. Bumpers tend to have lots of "fuzzies" when sanded dry. Cleanliness before adhesion promoter is critical to longevity. SPI 700-1 should be the final step before the promoter, and should be allowed to dry 45 minutes. Not all adhesion promoters are created equal, either. Bulldog is the worst, IMO. I've had good luck with the SEM products and SPI.
 
Like Texas I've done more bumpers than I care to remember. 320 wet or urethane safe bumper cover stripper to strip it. If you know someone who does soda blasting that would be a huge time and hassle saver. If you could get it soda blasted barring any damage to the bumper itself you could go straight to adhesion promoter then sealer (after a good detergent wash). Otherwise prepare for a lot of PITA sanding or scraping removing the existing finish.
220 dry would be a big mistake. Sand scratches would swell up like Jerry Lewis on steroids (google it :)) when you applied adhesion promoter over them.

Couple of good bumper cover safe stripper options from SEM

Paint Strippers | Refinish | SEM Products

www.semproducts.com www.semproducts.com
 
Great now I understand much better. It was my thinking that epoxy primer cannot be sanded and that's why I was thinking about 2K primer. So proxy primer is what I will use. That leads me to ask why do people use 2K primer. When would 2K be a good idea.
 
Siciliang35 said:
Great now I understand much better. It was my thinking that epoxy primer cannot be sanded and that's why I was thinking about 2K primer. So proxy primer is what I will use. That leads me to ask why do people use 2K primer. When would 2K be a good idea.
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2K is used in collision work because of the time factor, not because of quality. Imagine if you were a painter and the boss brought you that bumper to paint. He tells you there is 4 hours on the job. (~ $60) You find a way to get it done or you starve. Not saying it's right, just the way it is. I have sprayed many bumpers with Sherwin Williams P30 primer, and it is very flexible, but nothing will have the adhesion of epoxy
 
I understand so much better now. So for the epoxy primer that is also sandable, does that need activator or reducer. Is that both a primer and the sealer
 
Epoxy is both a primer and sealer.
It uses it's own activator that is very different than other primer activators
and can not be interchanged. Make sure the activator is for epoxy primer.
Reducer is interchangeable with other brands and can be used to thin a little
which makes it an excellent sealer. Or you can spray epoxy full strength without reducer.
 
Siciliang35 said:
Great now I understand much better. It was my thinking that epoxy primer cannot be sanded and that's why I was thinking about 2K primer. So proxy primer is what I will use. That leads me to ask why do people use 2K primer. When would 2K be a good idea.
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Epoxy is very slow to cure, it doesn't sand easily.
It can be sanded the next day but two days make it a lot easier.
Epoxy also has a very low build and it's not good to pile it on, so for
bodywork where you want higher build and less sanding times 2k is what most use.
I always put a sealer coat of epoxy on my bumpers after bodywork and 2k primer (if needed)
only because it increases adhesion lessening road rash.
 
Oh . So I came in here and I specifically asked what I should be using, specifically said I might be sanding it, and I was specifically told more than once that I'm missing the point and not use 2K primer. So this morning I woke up and I went to go get the painting material I need and I got epoxy primer.
I called the company they said it could be sanded but they only recommend one to 1.5 mill of primer on the bumper, so if I do have to do some sanding after I apply this primer should I add some 2K primer and sand it down

Or should I just do what you just said and do 2K primer and use this as a sealer
 
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You will find in painting there is more than one way to accomplish your goal. The absolute best way with what we have available today would be epoxy only if you can get away with it.

The other thing I want to highlight as I see you have edited your post now, but this site is geared toward Southern Polyurethanes products, SPI for short. Everyone is more than willing to help you out, but keep in mind when pretty much anything is discussed here and you use general terms like "epoxy", it is assumed you are using and referring to SPI. If you are not using SPI's products specifically then you need to be specific as to which product you are using since there are vast differences in the properties and qualities of the various "epoxy primers" on the market.
 
texasking said:
If you have plenty of time, multiple sessions with SPI epoxy would be the ultimate base for color and clear. It is sandable, unlike most epoxies
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@Siciliang35 If you try and sand any other epoxy, you will think you got bad advice. To me, SPI epoxy sands really well. Not as easy as 2K, but not bad at all. I sprayed 2 unreduced coats on some bare fiberglass parts Friday around 10 AM, put out in sun at 12:30 until 3:30, brought inside and fixed pinholes with glaze, sanded dry with 180 and re epoxied before I went home. The parts sanded fine and didn't plug the paper. Any other epoxy I've ever used would not work doing this.
 
SPI epoxy is just about all I use. It sands great. As a matter of fact, I just finished sanding some I had sprayed yesterday. Only other primer I use is the SPI turbo when I have to rush something. Epoxies are not all created the same.
 
Siciliang35 said:
Oh . So I came in here and I specifically asked what I should be using, specifically said I might be sanding it, and I was specifically told more than once that I'm missing the point and not use 2K primer. So this morning I woke up and I went to go get the painting material I need and I got epoxy primer.
I called the company they said it could be sanded but they only recommend one to 1.5 mill of primer on the bumper, so if I do have to do some sanding after I apply this primer should I add some 2K primer and sand it down

Or should I just do what you just said and do 2K primer and use this as a sealer
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SPI epoxy is what you should be using and since this is the SPI forum the advice you received is for SPI epoxy. If you’re using something else you need to follow the manufacturers recommendations. I can tell you that SPI epoxy is the best primer for bumpers by a very wide margin. I’ve used it many times on flexible bumpers with great results because it will not crack when flexed. Other epoxy primers will crack....

Don
 
Siciliang35 said:
Oh . So I came in here and I specifically asked what I should be using, specifically said I might be sanding it, and I was specifically told more than once that I'm missing the point and not use 2K primer. So this morning I woke up and I went to go get the painting material I need and I got epoxy primer.
I called the company they said it could be sanded but they only recommend one to 1.5 mill of primer on the bumper, so if I do have to do some sanding after I apply this primer should I add some 2K primer and sand it down

Or should I just do what you just said and do 2K primer and use this as a sealer
Click to expand...

What company did you call? If it's anyone other than SPI you are mixing up your sources. You can't call one product owner to get info on how to use someone else's. Now if you called Barry, then do what he says for his products!
 
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