47-55.1 Removing old paint and rust

[Stepside Jim]

Great answers.

Bonding, etch bonding, chemical bond, mechanical bond.
Etch, an acid effect, creating microscopic hooks into the metal for grip/bond.

Chemical bond, where two liquids both not fully cured, come together/bond by their solvents melting together becoming as one.

Mechanical bond, scratched, or microscopic pits left behind from media blasting. The adhesive properties of the Epoxy primer and the primer gripping the scratches and pits provides the bond.

Since we're focused on Epoxy primer, and notice both of you agree to let Epoxy cure fully before the next step yet, some Epoxy primer companies say you can spray over it as early as an hour, usually recommended 24 to 48 hours but before 5 days. During this first 48 hours, wouldn't this be a great time to use the Chemical bond method then prime with a high build primer or paint and skip the wait and sand then top coat?

Consider your answer since it has become extremely common to use Epoxy primer as a final sealer before final painting, using only the chemical bond between the Epoxy/sealer to the paint finish.

By waiting for it to fully cure are we not losing the chance for the chemical bond between high build primer and Epoxy primer.

Being a 2K product, does Epoxy primer not continue to cure when top coated with in the first 5 days?

When I look at the pictures provided in the original post, I see rust pits, pits that sand paper and wire brushing will not reach the bottom of the pit and leave the loose rusty specs behind in the bottom of the pit, blasting will get to the bottom of the pit and find clean metal.

Either way of blasting, sanding, or wire brushing, what ever primer you spray over the rusted pit you will not be able to sand scratch the depth of the pit once the primer is fully cured. Every pit will not provide bond since chemical bond is past tense and sand paper will not scratch the inner part of the pit. If you do try to force the sand paper into the pit you'll expose the metal surrounding the pit causing you to reapply Epoxy primer to coat the metal again.

Once again, a perfect time for the chemical bond, first couple days of Epoxy primer, to apply high build primer to settle into the pitted area and hold by chemical bonding or perhaps body filler over/forced into the pitted areas?

I'm not sure about the application of body filler in the first couple days using the chemical bond theory with body filler without sanding first, I cant find spec sheets on this procedure.

[gsinon]

Not all epoxies are created equal and some require much longer times then others to either topcoat or use as a foundation to then apply body filler.

If you are using the epoxy as a sealer and then going straight to surfacer or color, then you are in a way using the product as a sealer in which case you are using both mechanical and chemical adhesion. So yes, waiting the prescribed dry or flash time which can be as little as 30 minutes or as much as a couple of hours is all you need to do before spraying the topcoat.

In my previous reply about waiting for a full cure that was because I made an assumption that body filler would be applied as a next step. In that case, you really should wait the proper cure time. The styrene in body filler can slow or stop the curing process of epoxies if it is applied too soon.

As a "ppg guy" former tech rep and training instructor for ppg, I can tell you there are many different products and issues that can arise by not waiting or doing something out of sequence. When you look at a product like DP-LF, it can be used as a sealer in a "wet on wet" situation. However it still takes upwards of 7 days for full cure. At day four or five you can still take a finger nail and scrape it off of a panel, but by day 7 or beyond it would need to be sandblasted to remove it. But this is also why I don't like DP as a sealer. While it is still curing and gassing out it is casing my topcoat finish to tighten up or die back.

Have you ever used this type of product as a sealer, and when done the topcoat has amazing gloss and looks spectacular. But then about a week later it de-glosses some? Thats the epoxy going through the cure process days later and it is still releasing solvent and gassing out. There are better products for a sealer that won't let this happen. But, if it works for you and you are happy with the results then so be it.

And while I'm a PPG guy and only use their products, I do admit there are other brands and products that work just as well. Use what works for you. To me the biggest factor in what product line to use is what support do you get locally from your supplier?

[Lost in the 60's]

Look into SPI epoxy products. I use the 2k epoxy primer as a sealer also with SLOW reducer, to allow it to seep into all the pits and crevices as it flows out and sets up.
https://www.southernpolyurethanes.com/

7 day window to add filler, seam sealer and another coat of epoxy without any sanding. If sanding is needed, 1-2 day dry time will make the job easier without filling the paper. This stuff WANTS you to apply the filler and sealer and can be top coated with color on it during the window, for the best chemical bond. If after the window, a simple scuff with red scotchbrite, breaks the top skin and you can continue on with whatever stage you are at.
Epoxy, actually, takes several weeks to months to FULLY cure, so if sanding after a week, you are still cutting into soft paint.

As for sand blasting, that will never happen here again. Too many near impossible vintage parts destroyed by that process. I have a facility 300 miles away that dips parts to whole bodies in a non toxic mixture that removes everything but metal and rinses free of any acidic residue. He then has the parts dipped in EDP. Expensive ? YES, but worth it to have parts returned ready to sand and work on.
600 miles R/T, too far you say ?? It's all in what a person wants the end result to be.
Might want to see if there is anyone doing this method at a distance you are willing to travel. I'm a retired truck owner/operator, so long distances and hours in the saddle don't bother me, but 14 hours is starting to get a little old at 71 yrs. Your mileage may vary...

http://www.metal-cleaning-rsi.com/

[dsraven]

I always wait the required time after the first epoxy application because, firstly, I apply a good thick coat of epoxy and if there were rust pits those sections are for sure heavily coated. I try not to use a panel with rust pits that bad but if i do they get heavily coated. anyway, my point is, the epoxy needs to gas out on t's own thoroughly so I give it that time to fully cure before i sand on it. too early and it comes off the metal as you sand because it's soft. with a thick coat of epoxy it takes some time to gas off so applying another product on top means you may get a great mechanical bond but it doesn't matter because the gas from the previous coats is gonna come through and either make bubbles on the next coat of otherwise affect it. i have had the bubbles happen to me once. it took a long time to sand that all off and start over. not gonna do that again. maybe a body shop that works with new straight panels could pull it off with the chemical bonding theory but I will stay with my tried and true method.

[Stepside Jim]

Ok, good conversation.

My intent is to focus on the original post with the pics showing lots of rust pits and the rust roof rain rail.

I did however mention the concept of using Epoxy as a seal coat so the concept of chemical bond would have a clear vision.

I was also forcing the concept of using Epoxy first then body filler second to see if anybody would bring up filler first, then Epoxy. Most us in this discussion are into or past our 50's, we all never had Epoxy most of our automotive past. Here we are, 30 years later and our filler on metal cars are still hanging in there.

We all had Lacquer based primer for the most part, which didn't grab metal worth a darn. Perhaps acid etch primers too but they were very specific in application.

Back to the original post, the pit pics. Some, as we've heard, are not sand blast enthusiasts. In can honestly say I am not a fan of rust conversion chemicals. For the acid dipping, I do wish I was near a facility, but I'm out in the sticks, I have to mail order most of my needs as it is.

Perhaps there is still place for filler directly to sand blasted metal?

Let's clarify a candidate area for sandblasting. Back to the original pics, simply remove open, near flat sheet metal areas as candidates, leave that to the pros or experienced guys or last resort situations. The rounded areas are prime for blasting. The rain rail area is good to go, the rounded dash, absolutely, the rust pits on the roof edge, cautiously, but yes. All be it as mentioned previously, moving the blasting wand continuously and at an angle, never stay in one place.

Maybe rust conversion chemicals work maybe not, I just know for the time someone applies a chemical into a rust pitted area and waits for a dry time I can blast out the pitted area, see clean virgin metal, soak the area with a cleaner, skim coat the pitted area with filler, let it cure, sand smooth and coat with Epoxy.

The filler sticks to the blasted metal pits, the sanding of the filler smooths the high spots from sand blasting and we know the Epoxy will bond to the filler and the sanded metal. The pits are gone, the Epoxy cures for it's time, sand and apply high build primer. Smooth.

I'm not not advocating using filler before Epoxy, I'm a strong believer in Epoxy first. I'm just looking at this particular situation.

[dsraven]

Also, for what it's worth, a new roof skin on a regular cab truck could be more cost effective than blasting and finding rust through or really bad pitting. Really bad pitting is a recipe for rust through later in my book.

[leegreen]

One of the realities of restoring old vehicles at home is that the projects often start and stop. I see a lot of projects for sale that look like they got some surface prep then abandoned and bare metal rusted over, or primer rusted through. A lot of projects stall over the difficulty of painting in urban settings. The pictures in this thread look like the truck sat after the first sanding.

Not everyone can spray epoxy primer or iso hardened paint in their home shop or driveway. Make a plan before you start exposing metal. Any coating you put on is better than none. A rat rod patina finish is better than rusted over bare metal. A body shop that will paint parts as you prep them? Spray bombs and brushes at home? Money in the bank to send it off for body and paint?

this door is brushed on epoxy then brushed on tremclad/rustoleum. 5 years on after being stored under back deck it looked about like a 5 year old lacquer paint job of old. In other words the paint faded and it could use buffing, the door is spray bombed flat black now. Hardener makes the paint more durable, but as above spraying hardeners is not something everyone can do at home. I have the equipment, but not the location.

This is not the best way to do it and a better paint job may come along someday but the truck will be running and driving first.
A running driving old truck that looks like an old truck is way cooler to me than a wannabe show truck that is never finished.

Eastwood makes an epoxy primer kit for roll / brush on. I haven't tried it.

[dsraven]

yeah, good point LG. brush on or roll on can look pretty good and is better than nothing or spraying some bad chemicals without proper equipment. think about the people downwind and/or what you will bring into the house on your clothes after as well.
when I spray paint or primer I have a full face supplied air respirator connected to a compressor made for breathing air that is outside in fresh air upwind from any release from the shop. don't mess with your respiratory system, you only get one set of lungs. body shop prices or prices to buy the correct breathing equipment to do the job yourself would be cheap compared to the alternative. when sitting in the hospital with problems you would be cussing yourself out for not doing it right. also, wear disposable coveralls and proper gloves etc. the bad stuff gets in through your eyes and pores in your skin too so cover up boys and girls. when I see the guys on TV car shows spraying with just a paper mask on or you see guys doing a spot weld with no welding mask or grinding without even safety glasses on I just shake my head. long term pain for short term gain and not even their own vehicles makes it even worse.
google isocyanates in autobody paint for a run down on how it affects your body.