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View Full Version : priming bare metal...use rust converter just incase ?



illnastyimpreza
11-25-2008, 02:42 PM
I've sanded down all my rust spots to bare metal. BUT should I use a few coats of rust converter before I prime? is there any negative effect in doing so ?

I'm going to be using omni MP182 2k urethane surfacer. I'm told there is a difference between a primer and a surfacer. DOH. Can I use this as both?

I am painting over my factory paint(scuffed with Grey scotchbright and some paint scuff/wax&greese remover) I was advised to spray the entire car with the S.P. sealer first , then the basecoat. does this sound ok ?

On the base metal I will just be using the MP182, sealing, then spraying base.

anything I should change ??

illnastyimpreza
11-26-2008, 10:44 AM
anyone have any ideas?

Serge
11-26-2008, 03:52 PM
That's why you probably did not get any answers yet...

Urethane primer like MP182 does not go on bare metal. You need to put an epoxy primer on the metal first. (MP170 if my memory serves me well, I don't use those products...) The rust converter/metal conditioner part is not necessary if there is no rust left. Metal conditioners can actually hurt the epoxy adhesion depending on the product you are using. You need to completely remove the rust, sandblasting is the best way of removing it. Then epoxy primer, then surfacing primer.

A grey pad is not a good way to scuff an entire car. Its ok for hard to reach areas but I find it is not aggressive enough for an entire surface, you risk delamination as its difficult to put a good scratch in paint with just the pad. I would sand the car with 400 dry or 600 wet. Sand paper will make the surface completely dull and will have the advantage of somewhat averaging the surface by nibbing any imperfections. Also, you can not feather edge a repair with a pad, you need sand paper to feather in the areas you primed.

You can use the epoxy primer as a sealer, you don't need a separate sealer.

Look at the education portion of the site there is a basics section that covers all of the steps in prepping and painting...

illnastyimpreza
12-02-2008, 06:52 PM
awesome thanks.

so I guess all I need on the bare metal is the epoxy primer ? I ordered a half gallon, that should be enough for my hood and fender.

But what about plastic bumpers? does it matter what primer I use on that ?

also, I used surface prep wash with the pads, they are gritty and add some scuffing action along with the pads...as well as remove wax and greese :)

whats the best way to wash the surface clean before I spray ?

Serge
12-02-2008, 09:51 PM
If you spray 2K primer on a flexible part you must add a flex additive in it. Same is true for clear. So plastic bumpers usually get an adhesion promoter, a coat of epoxy (epoxy does not need to have a flex additive as long as you stay thin...like one coat).

If plastics need filling at all you need to use flex fillers and if you need a surfacing primer then you must add flex additive to it.

I usually wash the car with water to remove any sanding dust then let it dry over night before painting it. The next day I give it a once over with wax and grease remover then shoot.

Any plastic part gets a once over with an alcohol based cleaner (ppg's DX103) to lower the static charge...but you can skip that one if you don't want to buy another product.

Like I mentionned in my previous post, the basics pages in this website are worth reading as all of this is explained there...

Good luck...post pictures of your project...

illnastyimpreza
12-03-2008, 12:35 AM
thanks I'll have to check the how to out...

I can't figure out how to post pics, cuz it keeps telling me its invalid... How do I post photobucket images ??

here is the link to my current progress :)
http://www.rs25.com/forums/showthread.php?t=95326

Len
12-03-2008, 07:22 AM
thanks I'll have to check the how to out...

I can't figure out how to post pics, cuz it keeps telling me its invalid... How do I post photobucket images ??

here is the link to my current progress :)
http://www.rs25.com/forums/showthread.php?t=95326

If you click on the FAQ at the top of the page it will tell you how to UPLOAD a picture to this site. If you want to post a picture from Photobucket you right click on the picture then, on the drop down menu, click on "Properties" then highlight the URL of the picture and right click on it and copy it. Come back to your post and click on the yellow box (Insert Image box) at the top of the message block and paste that address in that block and click "OK". This will put the picture anywhere you have the cursor located in the text but most folks put the picture at the bottom of the post.

Once you do this a couple times it becomes quick and easy.

illnastyimpreza
12-03-2008, 08:06 AM
do I need a certain number of posts to start a thread? it still won't let me...internal error it says.

chopshoppe2004
01-01-2009, 03:10 PM
IF you go down to bare metal, you need to use a self-etching primer, then a good epoxy primer. Trust me, the potential for rust coming through is very good if you don't use an etching primer first. I don't care how good you clean it.

Len
01-01-2009, 10:10 PM
do I need a certain number of posts to start a thread? it still won't let me...internal error it says.

Try it now.

Len
01-01-2009, 10:13 PM
IF you go down to bare metal, you need to use a self-etching primer, then a good epoxy primer. Trust me, the potential for rust coming through is very good if you don't use an etching primer first. I don't care how good you clean it.

Why do you think that etch primer helps with rust? I've heard of guys using it under epoxy primer but it's usually because the products they are using are not the highest quality and can allow moisture to reach the surface. If good quality primers and top coats are used you can eliminate the etch because it really doesn't add much more protection.

showcar
01-05-2009, 11:10 AM
I'm not entirely sure but isn't it the acid in the etch? I know epoxy doesn't have anything in it that stops rust and it's only preventative measure is the great adhesion it provides. Just a little curious on that one.

chopshoppe2004
01-07-2009, 08:33 PM
Yes the acid in the etch primer eats away the microscopic rust that you may not get with sanding, but mostly is a cheap insurance. I always use quality Dupot product and the manufacturer recomends any time you go to bare metal to use a rust prevenative which includes etch primer. I don't claim to be an authority, but I did graduate from trade school and have been doing this for about 25 years.

All Dry
01-07-2009, 08:55 PM
Yes the acid in the etch primer eats away the microscopic rust that you may not get with sanding, but mostly is a cheap insurance. I always use quality Dupot product and the manufacturer recomends any time you go to bare metal to use a rust prevenative which includes etch primer. I don't claim to be an authority, but I did graduate from trade school and have been doing this for about 25 years.If you have been doing this for 25 years then you have me outnumberd by about 23 years that said.My impression of acid etch primers is that the acid just bites the metal(etches) for adhesion.It does nothing in the way of going after traces of rust.Logically how could the acid stay reactive that long to disslove rust?.I would not use acid etch primer before epoxy because some epoxys react to the acid and can cause delamination.Mike

showcar
01-07-2009, 11:38 PM
Yeah, it does bite but in doing that don't you think it's killing rust at the same time, and then no longer reactive?

illnastyimpreza
01-08-2009, 08:08 AM
hhmm so does acid etch kill rust or not ?? :o

showcar
01-08-2009, 08:55 AM
Yeah I think it does kill small flash rust.

If you think about it, even if it does, it can be viewed the same as a conditioner but it isn't allowed to drizzle into crevices as good as a conditioner due to it being sprayed, and probably doesn't kill flash as good maybe? Conditioner, according to members here may or may not have issues with adhesion and it seems the same with etch. It seems like if a conditioner is used correctly than that may be a better way.

This is strictly observation. Don't know first hand and don't knock anyone's opinion on this.

All Dry
01-08-2009, 09:48 AM
Yeah, it does bite but in doing that don't you think it's killing rust at the same time, and then no longer reactive?No I think the acid is only for adhesion.Acid etches are used in all kinds of ways even when you go to the dentist they will use phosphoric to etch a tooth to bond resin to it.IMO You should have your rust issues resolved before putting any finish on the panel.Mike

showcar
01-08-2009, 10:05 AM
I'm referring to rust you can't see. I did hear it does kill that rust and I heard from a reliable source, but he himself doesn't use etch much for the same reasons as people on here.

BradNes1
01-08-2009, 05:26 PM
I know of a number of epoxies that specifically say do NOT use acid etch of any kind under their primer (HOK being one of them). I know acids can interfere with the curing of true epoxies depending on their formulation so I would just be safe and go with what the manufacturer recommends.

alaskajeff
01-08-2009, 08:26 PM
I'll throw in my cent and a half: If your bare steel is smooth (not sanded or blasted) you need to use an acid etch. Either a wash, an etching primer, or something with acid to give it some tooth. If the metal is sanded or blasted, you can use epoxy directly. I personally believe the phosphoric acid in etch will convert microscopic rust. However, the better your prep (i.e., rust removal) the better off you are. If it looks orange, you're not ready. IMO, etching primer is not a substitute for clean metal. I have no experience w/ Picklex, but many folks here rave about it. I will try some soon.

I have some scrap steel out in the elements I've been experimenting with-etch over rust has resumed rusting through the etch. Where I sanded well, one coat of etch is still smooth, but turning orangish. Two coats still looks like new, except chalky. (Martin Senour Crossfire etching filler) This has been a year and a half. Interestingly, Rustoleum over rust looks pretty good, better than some spots on my frame which was prepped fairly well and has been kept covered up.

FWIW, Martin Senour Crossfire epoxy p-sheet recommends that "etching will enhance performance". Clearly, some epoxies can be placed over etch primes, but others apparently cannot. Best practice is to read the p-sheets and stay within a brand/system.

chopshoppe2004
01-09-2009, 08:27 PM
I talked to the Auto Body instructor at the local tech college and he is very pro etch primer on bare metal (sanded). I know quite a few people who do not and have good results. For my work, I use it. I use Dupont products and they do not advise against it. I agree totally that is all in your prep, and I'll leave it at that. This is turning into a peeing contest anyway.

illnastyimpreza
01-09-2009, 10:14 PM
well I did my damndest to sand the CRAP out of the hood(60 120 then 180) before I sprayed my primer. I followed the instruction from the company I bought the paint from. Do you think that rust will re-apear in the future since I sprayed epoxy primer over the metal ? I hope not ! If it does I will hopefully have a sandblaster by then, and will be able to go that route...and will definatly switch to acid etch for bare metal...

http://www.southernpolyurethanes.com/perfect%20paint.htm

Harry Phinney
01-09-2009, 10:59 PM
well I did my damndest to sand the CRAP out of the hood(60 120 then 180) before I sprayed my primer. I followed the instruction from the company I bought the paint from. Do you think that rust will re-apear in the future since I sprayed epoxy primer over the metal ? I hope not ! If it does I will hopefully have a sandblaster by then, and will be able to go that route...and will definatly switch to acid etch for bare metal...

http://www.southernpolyurethanes.com/perfect%20paint.htm
Whether or not to use an etch primer or other acid treatment is partly a religious issue and partly a question of what you intend to apply over the top of it. What you did was fine and you should not have any trouble. Do not apply any acid treatment or etch primer if you intend to continue to use the SPI epoxy primer. SPI's epoxy primer is incompatible with etch or other acid treatment. This is also true for Valspar epoxy primers.

Harry Phinney