Technical Difference in Primers

Have you ever asked yourself what TYPE PRIMERS SHOULD I USE FOR MY PROJECT, WHATS THE DIFFERENCE BETWEEN SELF ETCH, EPOXY, URETHANE AND LACQUER AND WHAT DOES 1K AND 2K MEAN? If you have, here is a quick run-down on the primers.

This is a question I get asked the most, and using the right primer is like choosing what type of foundation you are going to use building your house. So what I will do is go through all the different type primers and explain their features and benefits, and where you would use them.

First off is the difference between 1k and 2k primers. The "k" in primer stands for component, but in Europe it is spelled with a "k" (ie Komponent) So a 1k primer means only one component so just the primer is needed to spray on a panel. 2k primer means 2 different components so the primer and a activator is needed before spraying on a panel. A reducer or thinner is not considered as a component, just the hardener. Lacquer primers and self etch primers are 1k primers. Epoxy and urethanes are 2k.

Lacquer Primer - This is still widely used due to its seemed cost point, but if you consider how much dry film build a lacquer primer gives you, it is the most expensive primer to use, and the worst. It can reverse to a liquid, it can react when topcoated with another product, it does not provide rust resistance nor corrosion protection.

Self Etch - Self etch has been used for years, and for a lot of paint companies they still make you use if a warranty will be covered by them. Self Etch is a acid that basically burns its way into the metal. Self Etch does not harden like a urethane or epoxy, once dry, it can reverse back into a liquid state. Self-etch is excellent for corrision protection and adhesion to most any type bare metal, but is not recommended to sand. Self-etch does not have much film build, so if you sanded your car with 180 grit sand paper and wanted the primer to fill in the scratches, this will not do the job. You can however put a coat or 2 on the panel, let it flash then topcoat it with a urethane primer. This primer is good for a restoration or a new aluminum panel.

Urethane Primers - These primers are used in 90% of production body shops across the US. Urethane primers offer excellent build, quick drying, sands easy and are not reversable which means once it is hardened it can not go back into a liquid state. Urethane primers though, do not have good, if any, corrosion protection, they do not help in the prevention of rust and do not have good adhesion to bare metals. So if you are just repairing a couple of dents in your fender or door, this would be the primer for you.

Epoxy Primers - Epoxy primers are the ultimate in adhesion and corrision protection. They also provide excellent film build. Epoxy is the best choice for a restoration because it helps resist moisture. Since most restorations take over a year to complete (except for on t.v.) Epoxy is a great choice once you have completely stripped the vehicle down to bare metal, You can do body work on top of epoxy, Body filler sticks well to sanded epoxy. You also can paint over epoxy (not recommended with self etch because the TiO2 (white pigment) will turn a browish tint when applied directly on top of self etch) On the downside, a lot of epoxy primers take a long time to fully cure, some shops claim epoxy does not sand well, thats usually due to the epoxy not being fully cured yet. However some epoxy primers now can be accelerated to dry very fast with the ability to sand very easily, making epoxy the all around best choice to use for most any project, especially restoration.

 

Thanks for taking the time to post this. Very informative.

 

Thanks for this rundown. Follow up question. Which primer would I use as a non painter doing rust repair where it might not hit a paint shop for six months to a year? I let them do final body work, primer, etc. I also want easy to spray and clean up and have no experience beyond spray cans.

 

Thank you for this information. I have always never understood the difference in the types of primers. This makes it easier to determine what product to use for what job.

 

Good info!!

 

If possible use epoxy. It's easy to spray, you would clean your gun just like you would with any other primer. If you run the primer it's OK but epoxy has a tighter film so that no moisture can get through. Even though it will fade the coating itself isn't breaking down.

We did a test against rust converters, moisture cure urethanes and epoxy right over pitted rust, to see how long it would take for rust to reappear on the top surface, these were all products we made in house. We left out in weather. The rust converter lasted about 3 months, moisture cure about 2 years and epoxy 5 years but could have been a little sooner, we forgot about it. I don't recommend spraying anything over scaled rust. And a rust converter is really only meant for areas you can't get to with a wire brush. Rust converters don't have any solids to them so as time goes moisture can get through. Sorry long winded answer.

 

Thanks for sharing your knowledge Paint Guru, I have seen alot of your post lately helping others out.

When I was working on my car i was also looking for something cost effective(cheap) but already knew about the downfalls of using lacquer. I spoke with an uncle who paints and he suggested a water based primer. I tried the brand he recommended and was very happy with it. It seemed to have high build qualities that the lacquer did not. The only downside was the wait time afterward. This was for my personal car so it was not a big deal, i could see where the wait time would not be good in a shop environment. Cesar

 

@Paint Guru

Rust converters are just that a converter correct? They make a chemical reaction with the oxidized metal that in theory should render it benign or harmless. Am I off base here?

I have had a question about lacquer for a while, when I was younger we used to pickle bare metal before shooting lacquer primer. Obviously shooting lacquer was the intended end of the paint job. I have been told that you can shoot lacquer over epoxy primer, I already know that you *shouldn't shoot lacquer over enamel. Can you shoot lacquer primer over self etch primer and can you really shoot lacquer over epoxy or no?

*shouldn't being the operative term here it can be done for a desired effect but not commonly considered good painting practice.

 

subscribe

 

Great info.
Is there anything special those of us dealing with Fiberglass bodies need to do when it comes to primers?

 

Yea water based works well, we have built thousands of gallons of dtm water based for industrial. It does well however it's a soft film so it will absorb water. So it needs to be top coated soon. And dry time is based on humidity. High humidity = slow dry times. One tip for water that the Enviro-natzi's frown on (and your wife) is a hair dryer. Just point it to the primed area.

The reason most body shops use urethane is the speed of cure. So even compared to lacquer if you put on thick you can get urethane to dry faster to sand.

 

Thanks for the post. I have a quick question, ive always wondered why not use a coat of self etching primer on bare metal, then wait for flash time and spray on epoxy. Wouldnt you get the absolute best results in every aspect of the primer' characteristics?. I tried it once on a scrap piece of metal and used a dupont self etch and a nason epoxy and they did bond. Ive never heard of anyone doing this, but wouldnt it be best for our old cars, that we all want to last the test of time.
What do you think?
Thanks

 

Rust converter can only convert the top surface. But yes you are correct on being harmless after converting to a extent.

I am not a fan of sandwiching 1k products between 2k (2k primer and 2k topcoat ). And I am really not a fan of lacquer primer unless it's used as guide coat and it's going to be sanded off. But yes you can shoot lacquer over epoxy, urethane and self etch. But you can buy urethane for $85 kit in 100's of places, lacquer is around $50 roughly. You only have to prime once with urethane to get 180 grit scratches out, lacquer you have to prime, block, prime and block. Then you have to seal lacquer before topcoating (another $35 for quart of sealer) so lacquer cost you the same as urethane but lacquer cost you an extra 5 hours in labor and it's not durable on top of that. Just food for thought because i know lacquer is easy to use because you can leave in the gun, sands super easy etc. But in no way is it a product I recommend. We make it because there are people you just can't convince, but if you are putting time into a project and it basically cost the same in the long run and saves my labor , count me in!

The reason for the dislike of lacquer is if you have ever seen Paint blister it's because the solvent in the paint you are spraying (if spraying basecoat on top of lacquer) the solvent that's in the base softens the lacquer and makes it blister. Just like if you have ever spilt Paint thinner on new paint. Hope my rambling makes sense.

 

For Fiberglass the 2 products I recommend are epoxy and polyester. Polyester primer is basically spray able body filler. It cures with Fiberglass hardener so you have a good chemical bond. You can build polyester pretty thick and this helps with all the pin holes around edges on fiberglass bodies. One brand of polyester primer no one really uses but is less expensive than some of the more popular brands and is a good quality is USC part number 300-1.

 

Great info. Thanks.

 

Good Post, THANKS for the info.

 

Can a urethane primer be used over an epoxy primer then sealed before top coat? Or would it be best to use the epoxy alone? After you wet sand the epoxy do you need to use a sealer before topcoat? Does a Sealer need to be used before topcoat on urethane primer? I am about ready to start putting my frame and other parts into paint and was wondering what is the best choice. I will prolly use a single stage acrylic urethane for top coat.

 

You could I guess but there really is no benefit for putting both. Epoxy bonds tight to metal. Think of it this way panel bond that's used to glue metal panels together that has a higher strength per square inch than a weld is epoxy. Once epoxy is cured nothing gets passed it. It's corrosion resistance is far superior to any other undercoat. Epoxy has a chemical bond of well over 1500 lbs psi. If you put epoxy first then a good polyurethane top coat and keep it up with regular washes and waxes and the underside is undercoated with a epoxy, it will stand the test of time.

 

I actually am using lacquer because I have lacquer and it is in a color that I like. Well that and if you are willing to rub it produces a pleasant result, well pleasing to the eye of some. I also like the look of single stage enamel. just an odd duck I suppose and I have shot both with good success.

I have not yet purchased my base product and have been on the fence with it. Urethane and epoxy has been on the back of mind and if it will work then I am good with it. I think I can get wither tinted locally cheap enough to be budgeted in. I prefer to shoot lacquer over a tinted base because it seems that most lacquers have some degree of translucence the final color is effected by the base it is shot over. Maybe I am completely off base or it is a quirk that I got.

 

Ok you are talking about a lacquer as a topcoat I am sorry I was talking about it as a primer.

 

I am use lacquer as a top coat, wondering if I can actually shoot it over epoxy or if that is something that some said because they heard you could. You seem knowledgeable enough to know or at least have tried.

 

Yes you can shoot a lacquer topcoat over an epoxy with no issues at all.

 

Thanks. That makes paint easier. Well in theory easier, LOL. It also means I have to measure accurately.

 

If you like lacquer, I would consider enamel. Enamel can air dry, you can put a hardener in it. It accepts a acid similar to a rust converter for direct to metal application, easy to buff and fairly easy to get anywhere. With no hardener it has about the same life as a lacquer, with a hardener you double the life span. Food for thought.

 

My past practices have been to use epoxy on the bare metal, followed with 2k urethane for fill/blocking, then I seal with the epoxy just before I shoot color.

 

Nothing wrong with that. I typically don't seal but that's my personal preference, and depending on the substrate.

 

The lacquer is paid for otherwise I would probably be shooting enamel. I don't mind rubbing at all, just confirming before I spend what little cash I have on hand for my base.

 

Just let me know when you are ready for color I'll do you right. It will be so inexpensive I could probably write it off as charitable contribution lol.

 

May take you up on that.

 

I have a few bubbled up rust spots on my car. I have no idea what it was repainted with, but I'm guessing it is enamel. I know it's a single stage, no clear. I have limited time to work on the rusty spots, and I'd like to fix one or two at a time, then brush some epoxy primer on the repaired spots and then go back later and give the car a total sanding and epoxy prime the whole thing. If I could do it that way, I could still drive it while I'm doing the bodywork, and I wouldn't have to mix up a gun full of epoxy for a few half dollar sized spots and have a bunch of waste. Or would I be better off to just fix several spots, give them all a quick sand and spray a gun full of epoxy on all at the same time? All the work will done under my open on two sides carport.