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Epoxy on new panels

8K views 72 replies 11 participants last post by  BarryK 
#1 ·
Can I use epoxy primer over the primer on new panels or should they be sanded to bare metal and primed with etching primer ?
 
#3 ·
I learned something a few years back talking to an OEM paint engineer. He said they don't want the e-coat roughly sanded that each manufacturer has a set amount of mils they want for maximum adhesion and corrosion protection.
He stated they like to see a Grey scuff pad not a red because the Grey is finer and lite scratches put in the ecoat with very little taken off.
I learned scuffing with 180 and when done 80% of the ecoat was gone, guess I learned wrong!

Yes epoxy works great over ecoat.
 
#4 ·
Rule #1: assume nothing, buyer beware

Rule #2: do the research, get the facts on your panels

The coating on your panels:

"maybe" laquer based transport primer on slick steel, needs to come off,

"maybe" crummy thin cheap e-coat on slick steel

"maybe" correctly applied e-coat,

I've never found "good" e-coat on any Mustang imported panels.

Strip it, 80 grit it, epoxy it, atleast any areas that get abuse from stone chips, moisture, etc.
 
#5 ·
red65mustang said:
Rule #1: assume nothing, buyer beware

Rule #2: do the research, get the facts on your panels

The coating on your panels:

"maybe" laquer based transport primer on slick steel, needs to come off,

"maybe" crummy thin cheap e-coat on slick steel

"maybe" correctly applied e-coat,

I've never found "good" e-coat on any Mustang imported panels.

Strip it, 80 grit it, epoxy it, atleast any areas that get abuse from stone chips, moisture, etc.
Why in the world would you want to "80 grit it"? If you strip it, you should be able to use 180 grit at the coursest, to get good adhesion, although I don't feel that it needs to be striped, unless there is damage to the e-coat. 80 Grit would be fine if you need to use it to strip.
 
#6 · (Edited)
red65mustang said:
Rule #1: assume nothing, buyer beware

Rule #2: do the research, get the facts on your panels

The coating on your panels:

"maybe" lacquer based transport primer on slick steel, needs to come off,

"maybe" crummy thin cheap e-coat on slick steel

"maybe" correctly applied e-coat,

I've never found "good" e-coat on any Mustang imported panels.

Strip it, 80 grit it, epoxy it, at least any areas that get abuse from stone chips, moisture, etc.
************************************************
Lacquer transport:
never have seen it or herd of it! Are you thinking of Cosmoline?

Maybe correctly applied or crummy:
No mater what we do we cannot create a rust free metal and adhesion as good as manufacturer. Example Nissan is building an e-coat place in MS as we speak--a five dip tank process.

Bad Mustang panels:
Where you buying these from? I just sold 22 mustangs and have bought many panels from Year-one and worst I have seen is a ping ding. The year one 66 blue stang, all year one panels and scuffed and shot with epoxy. Quarter was wrecked two weeks ago when battery broke lose in trunk and paint was not falling off.

bwk

http://www.southernpolyurethanes.com/images/MVC-406F.JPG
 
#7 ·
Barry,
Ive seen some of this cheap Lacquer "transport" coating.
Ive NEVER seen it on panels bought from a resto house like Year One or Goodmark. But get some of your A/F collision repair panels. The last shop I worked at in Northern Iowa we did TONS of chevy truck cab corners and rockers(88-98).
Every once in awhile you would get a a part coated with a cheap coating that would wipe right off to bare metal with Lacquer thinner.

Looked like regular ecoat but put a rag with thinner on it:eek:

Ive bought more parts then I care for for my three 70 chevelles from Goodmark. Never once have I had a cheap coating applied to them. Just a good scuffing with 400 on a da sander then epoxy or regular primer surfacer...Eric
 
#9 · (Edited)
replies to my post

To adtcart: why 80 grit?
The PPG DPLF spec sheet calls for 80 to 180 grit prep on bare steel. It also call for minimum .75 mils to 1.5 mils dry film thickness.

The epoxy is a barrier "skin" on the steel, the epoxy adhesion to the steel is primarily mechanical, it grabs the "scratch", the 80 grit deeper scratch forms a stronger linked skin.

Actually, I use the grit that seems most appropriate for the area, ex: use a DA with 180 on the hood (less heat).
To be sure there are no thin spots, I lightly hand sand enough 80-100 scratches that: no scratches in the dried hood = no thin spots. I hand circular scratch lightly with (used) 60 on the edges for build.

To BarryK:
Go back and read the original question from "Gasser", it doesn't say what the panels are or who made them, that's why he needs to find out what they are coated with.
Unless like you, he is going to sell the car(s) when it's finished, then it's their rust problem.

Your comment about "the paint didn't fall off" after the accident: Epoxy (or good e-coat) is for rust protection not paint adhesion. It's applied to make the steel last longer, not the paint.

Transport primer, crummy e-coat and good e-coat all look exactly the same on a panel.
Haven't you ever wondered WHY imported Mustang panels are so cheap ($59 door skin, $59 qtr skin, $39 valance).
Their not going thru a 5 stage e-coat process at the Nissan plant you mentioned.

To everyone, my "e-coat?" test:

I don't trust the lacquer thinner rub test alone. Like I said, they all look the same on a panel.
I coat a small area of the panel with Jasco Premium Epoxy and Paint stripper ($8/qt Lowes, great product***!)
If the Jasco goes dry in 15 minutes and literally "pops" the ecoat off, it's transport primer or crummy ecoat.
If the Jasco stays wet and gummy (but the ecoat wipes off easy with steel wool cause the steel is slick) it's probably good e-coat.

***for stripping enamels, fantastic! After 15 minutes it pops off the paint in DRY sheets, use your shop vac for a no mess clean up.

Steve

apology to "Gassman", I told BarryK to read your question from "Gasser"

to many memories of the old Willys and Fiat AA/ "Gasser" days, they were insane cars....

Steve
 
#10 ·
Re: replies to my post

Your comment about "the paint didn't fall off" after the accident: Epoxy (or good e-coat) is for rust protection not paint adhesion. It's applied to make the steel last longer, not the paint.

**********************************************
Glad you have it figured out, but this statement is totally wrong and tells me your just reading tech sheets as you don't understand what epoxy really does.
Glad you got it figured out.
Barry
 
#11 ·
Well... I use 180 to prep bare metal for refinishing. If you count on the depth of the scratches in the metal to tell you the thickness of the finish, you are going about it wrong. That only tells you how thick it is inside the scratches, not on the outside, where it will be considerably thinner, unless you can still see the scratches.

I am not a paint expert, but know what has worked for me for alot of years. I use 80 grit to remove paint, body filler, or metal. To me, the idea of removing that much metal for paint adhesion doesn't make sense.
 
#12 ·
:smash: im with the 80 grit guy, ive used disk grinders to strip paint, like to start with a rough surface to put my epoxy on , since the epoxy is a slow dry paint it flows in the scratches to bite better. i use a epoxy called tenemec,its the toughest stuff i ever seen, after being cured it just about cant be burnt off with a torch or blasted off, i like to put it on before i bondo then put a hefty coat after i dodo to seal it,then i start my urathane primer with my flowable finishing pudy.
 
#13 · (Edited)
reply to adtkart

I do agree with you, 180 grit is plenty of "tooth"/scratch to get good adhesion on bare steel, on the hood, roof, trunk, any area that doesn't get abused, hit with stones and is subject to chipping like door edges.

Heck! I'll agree with you more than half way. Strip the transport/crummy e-coat off a $59 Mustang quarter skin, sand the bare steel with 180, BUT, hand sand the lower rear section with 80 grit for more "tooth" for the epoxy to grab to make a more impact resistant stronger linked skin to resist the stones the tires throw. Yeah, you will get chips but less with the 80 grit sanding scratches.

If you strip off the the transport primer/crummy e-coat off a quarter panel skin, then lightly sand just enough to thoroughly scratch the bare steel with 80 grit, it would probably require a lab scale to weigh the steel you removed.

About the peaks and valleys on the metal scratch surface, 80 grit is the limit based on the consistancy and slow dry/ flow of epoxy to not have thin spots on the peaks.
If your worried about thin peaks, coat it again.
What you gained with the deeper scratches is more surface area for more epoxy to grab, to make a stronger skin.
I do spray enough passes on the panel that the dried surface has a slick, smooth, semi-gloss finish when dried to make sure the peaks are not thin.

So back to the beginning:
Are you sure it's good e-coat?
If not, remove it, sand it with 80 to 180 grit, apply .75mils to 1.5 mils of epoxy for a rust resistant skin to protect the steel per PPG spec sheet #p-196.

I use 80 grit to to get the strongest "mechanical" bond possible of the epoxy to the steel

Steve
 
#17 ·
I think you missed what I said I use 80 grit on steel when doing filler. 80-180 on alunimum.

NO WAY do you need 36 grit for filler to stick to metal. Take 36 grit to a 2003 Chrysler 300M hood and find out what happens:eek:

Since this is painting basic 101 did you know the average OEM paint job is 6-9 mils thick. Roughly the thickness of a paper business card. Most warrentied film thickness is 14 mils, which what PPG suggests as the max thickness for them to warrenty the paint. And you are putting on 150 mils of epoxy!!!!
HOLY F%^*:eek:
 
#18 ·
I must have been brain dead

To BarryK and sevt_chevelle,

I went back and deleted almost all of my last post, I have no idea why I kept writing 150 and 300 mils.

Barry,
My math was wrong (so I deleted it), but so is yours.

"300 mils to fill 36 grit, try 1.23 mils it will work better"?

1" of paper/36 grains per inch = .027" (27 mils) grain size

sevt_chevelle,
I deleted the 36 grit plastic filler tooth analogy.
You need to delete "take a 36 grit to some of them" from your post because it reads that you do use 36 grit for epoxy prep.
That's why I wrote "36 grit for epoxy, your kidding right?"
No you don't use 36 grit on a hood for anything, twice I wrote use 180 for bare steel epoxy prep on a hood.

your paper business card thickness equals all the paint layers thickness (10 mils) is correct, I measured about 10 different ones, all were very close to .010" thick.

Another way to visualize it is 3mil construction/drop cloth polyethylene sheeting, it's pretty accurate.

A 6 mil OEM finish is 2 layers of 3 mil poly, God that looks thin, amazing what those robots can do.

To help visualize .75mils plus of epoxy thickness, a kitchen trash can liner is .95mils thick. You need a magnifying glass to see the thickness.

Lets see, a stack of 30 (10mil) paper business cards is 300 mils of coating thickness, oh yeah, I'm OK, really I am, just ask my doctor.
 
#21 ·
Figure it out, resin coated disc's grit are sunk in the resin unlike 6 inch DA paper.

Your talking 20,000 rpm vs 1000?
The percentage will also very by coarseness of grit such as 50 vs 16.

This don't make a hill of beans and is a waste of discussion but proves tech sheets tell you only what they want you to know and very few things in this business you can just make a blanket statement.
 
#22 ·
Barry, how deep of a scratch will this make

Measured the grit and paper thickness of a new Norton Red Resin 60 grit disk without the silicone backing. It measures .038" (38 mils) thick.

Filed the grit off to the resin. It measures .025" (25 mils) thick.

So the new 38 mil thick paper with grit minus the no grit left 25 mil paper = 13 mils of grit not imbedded in the resin right?

Hey, that means that 80% of the 60 grit .016" grit grain wasn't buried in the resin right?

How deep will new 60 grit paper cut with .013" (13mils) of exposed grit cut?
 
#23 ·
Wait a minute! Every time you get called you edit your post or change story.
We were talking about 36 grit.
Also where did you find red Norton grinding dics the blue is their big seller, stronger more coating.
The main players are Green-3m
Blue-norton
Give it up this is useless and meaningless.
 
#24 ·
congratulations Barry

you got one thing right!

As the grit gets finer (ex: 36 grit and 80 grit), the grit is buried deeper in the resin, it does cut less deep grooves, the resin has to have more of the grit grain surface area to keep the grit on the paper,

pretty logical huh.

Sorry, rpms has very little to do with cut depth. It's the pressure applied while sanding that determines the cut depth
 
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