Topic: Scuff or not to scuff - scratches in good sheet metal

[livetoride60]

Having a discussion with my paint guy on my engine compartment.  I've stripped the inside of the compartment with stripper, and have bare metal in excellent condition to work with.  He'd like to scuff it up to help the paint stick.  He'd also like to power sand the remaining paint off the outside (well wells, front of radiator support).  I'm very leery of letting him power sand the sheet metal, as I'd like him to paint the front end, firewall forward, with just primer and black, no filler. 

I have a friend who is what I consider a high-end Mustang restorer, and he warns against letting him power sand or scuff.  My friend prepped his engine compartment by stripping, rubbing down with lacquer thinner, then using medium steel wool in the corners.  He has done many Mustangs and has not had problems with paint coming off in the engine compartment or wheel wells.

Am I being overly concerned here about the power sanding or scuffing, or is there a better way?  He intends to scuff the bare metal with a scotch brite, not sure what grade.  I also don't know the sandpaper grit on the power sanding.  I definitely don't want scratches in my sheet metal.  Any thoughts would be appreciated.

Pics included of my bare engine compartment, what's left on the wheel side, and two pics of how I'd like it to look when finished.  I think those last two are from Charles and Brant (VCM), respectively.

Thanks,
Rich

[jwc66k]

Your painter works for you. If you want specific methods used (no scratches) or effects required (orange peel) and are willing to pay for them, then the painter should do them. Otherwise find another shop.
Jim

[livetoride60]

Thanks Jim.  I spoke with my painter this morning and agreed to let them scuff the bare metal with a scotchbrite by hand, but to strip the remaining paint with chemical stripper instead of power sanding with a DA sander.  He assures me the scotchbrite scratches will be small enough as to not be visible after application of no-fill primer and black.  I felt more comfortable after I realized the scuffing would be done by hand.  Still not completely sold.  If unscuffed bare metal was good enough for Ford & lasted 50 years, seems it isn't needed here, but I understand it does promote adhesion.

Anyone scuff or not scuff when redoing engine compartment or other sheet metal?

I am glad to not have to worry about someone leaning on a power sander & gouging my metal at least.

[J_Speegle]

Anyone scuff or not scuff when redoing engine compartment or other sheet metal?

After I prepped my Boss's engine compartment I scuffed it with a pad before and after the primer

[RocketScientist]

Just some background………

Paints primarily stick to metal, plastic and old paint by mechanical means – it is by physical attachment only. These surfaces are generally smooth and that makes the attachment weak and the best way to overcome that is by keying or roughing the surface. This roughing can be done by blasting, sanding or scuffing.  As long as you make the roughening process sufficiently fine so that the scratches won’t show through the paint, then all should be OK. For example, if you scotchbrite a steel panel you will see it come up shiny and most of the time you won’t see the scratches in the metal.

Most old car parts are painted with enamel and that gets exceedingly hard with time. If you chose to paint over it then sanding is a must as new paint will not stick very strongly to it. The worst effects I have seen are in hot humid climates where the paint expands and contracts a lot. It will show up in paint blisters on freshly painted cars that appear after the first summer rains or paint that easily chips off plastic parts. An extreme case I know of was when someone painted an old wooden house without any prep work. A few weeks into summer and the paint came off – in complete wall size sheets! You can guess he wasn’t very happy.

This is a long-winded way to say that any good paint prep needs proper sanding and scuffing to get the best result. However, you’re right in only allowing the paint shop to do what you’re comfortable with.

[Toploader]

Wonder how they managed at the assembly lines. Don't think scuffing was part of the process.

[CharlesTurner]

Treating the metal with phosphoric acid will etch the surface and give the paint more bite.  My guess is the factory washed or dipped the car in something like this before the painting process.  Products like Ospho accomplish the same thing.

A lot of individual bits and pieces were typically zinc plated as a primer base, which also must help with paint adhesion.

[Toploader]

Of course, then there was e-coat. But that was not until later. Or...? When did they actually start to e-coat Mustangs?

Wiki says first systems began to emerge around '63:

Electrophoretic coating began to take its current shape in the late 1950s, when Dr. George E. F. Brewer and the Ford Motor Company team began working on developing the process for the coating of automobiles. The first commercial anodic automotive system began operations in 1963.

[drummingrocks]

Of course, then there was e-coat. But that was not until later. Or...? When did they actually start to e-coat Mustangs?

Wiki says first systems began to emerge around '63:

Too bad Ford didn't e-coat the inside of the cowl!

[J_Speegle]

Of course, then there was e-coat. But that was not until later. Or...? When did they actually start to e-coat Mustangs?

Think it was used on some body panels in the late 70's early 80's

Would not even consider it on an engine compartment of a classic Mustang - just would not look right and how would you do the over sprays

[FredG]

Hey Livetoride,
You seem pretty obsessed with the prep method your painter is using, (since he is working for you, you very well should be), but I was curious if you discussed what paint and color he'll be shooting the engine compartment, rad support and aprons with.
Fred G

[jtfx6552]

Scuffing is your friend. Nothing to be afraid of.

The reason old paint stuck so well was lead. Try and remove 60s red oxide, that stuff sticks!

[livetoride60]

The reason old paint stuck so well was lead. Try and remove 60s red oxide, that stuff sticks!

Thanks for the info.  I was wondering.

You seem pretty obsessed with the prep method your painter is using, (since he is working for you, you very well should be), but I was curious if you discussed what paint and color he'll be shooting the engine compartment, rad support and aprons with.

I'm not sure if obsessed is the right word, but I have definitely learned in my career and hobbies it pays to be thorough up front if you want to reduce risk of issues on the back end. 

He'll be putting down red oxide PPG primer first, then a satin black after that.  Can't remember the brand of the satin black, but I've seen the results and they look good IMHO.  I've shown him pictures of my original spray patterns, with the black looking like it was shot top down, with red oxide still visible on the underside of the front frame rails.  The engine compartment, radiator support with this satin black will end up with less gloss than the semi gloss black on the engine and things like pulleys.  Definitely above flat though.  This is my understanding of how it should be.  Please let me know Jeff, Charles, anyone if not.

I've had a couple body guys report this paint combo stands up well, with one showing me an example of a 10 year old job that still looked good.  That car wasn't a daily driver, but was driven on occasion to shows, etc.

Scuffing is your friend. Nothing to be afraid of.

Yep, as I noted in an earlier post I agreed to have them scotchbrite by hand.  As you state, mechanical adhesion is a good thing.  My concern was they wanted to power sand initially to strip the paint, and it's easy to gouge the sheet metal that way.  Even if it can be filled, I saw no reason to "ruin" my nearly pristine sheet metal in that way....and I had heard others talk having gouge marks from this shop for that very reason, power sanding. 

So now I feel comfortable with the process, and the shop has been very accommodating while still offering guidance based on their experience.  Thanks all for your opinions and input.

Will post pics when it's done.

Thanks,
Rich

[Bob Gaines]

Keep in mind that the overspray from modern guns is tremediously LESS then that of the old guns like were used.The little overspray the new guns can put out can make the job look almost taped off in comparison to the overspray the old guns put out  .

[67gtasanjose]

Keep in mind that the overspray from modern guns is tremediously LESS then that of the old guns like were used.The little overspray the new guns can put out can make the job look almost taped off in comparison to the overspray the old guns put out  .

Has anybody ever worked with one of those old pressure pot systems? I imagine it was like painting out the sprayer of a garden hose! You likely won't find anybody who was a line worker as a painter from the 60's left alive past the early 1990's.   OSHA is a good thing!