Carc to Urethane

[01GRANDER]

What prep work should be done going from Carc to urethane? Is there a certain primer I should use?

I am planning on getting a 1 stage kit from TCP global and I want it to adhere well and last a long time. I may end up getting a 2 stage kit, it just depends.

 

[Ray70]

I do mostly high end automotive restoration work, but I have also painted everything from excavators to military equipment and everything in between. My current personal preferance is a 2 part epoxy primer. It will adhere very well to everything including bare steel with no adverse reactions to other previous paints. It is also the most moisture resistant of all the primers available, thus providing the best long term corrosion protection. You can top coat it wet on wet or it also has a 1 week recoat time without the need to scuff or sand, unlike the narrow 24 hr. window of a 2K urethane primer between sanding and top coating.
I like PPG's DPLF line but it is fairly pricey. You can get their Omni line much cheaper. I have also used 5 Star which is a good economy epoxy.
This is assuming you want just a primer or primer / sealer. The epoxy in my opinion it too hard to use as a primer / filler if you are trying to prime and sand to remove imperfections. For this I would use epoxy as the barrier base layer, then 2K urethane over that for you sandable layer. After wet sanding the urethane I would use the epoxy again in a 4/2/2 mix as a wet on wet sealer before your final topcoat.
This might be a bit overkill depending on what you are painting and your desired outcome, but it will last a LONG time.

 

[teletech]

Right now there is a lot of PPG aerospace epoxy primer on the secondary market (Ebay, etc.) for very reasonable prices. Mostly just expired Boeing surplus. I picked up a small pallet worth a few months back.
If you do use DPLF, be very sure to honor the specified induction time. Complaints about about adhesion and it seems like that is the likely culprit.

 

[Ray70]

Teltech is correct, read the data sheet. If you use the DP- 401 activator there is an induction period that must be adhered to. If you use the quicker -402 activator there is no induction time.
Think i will check to see what's left on ebay. Only thing to keep in mind is that epoxy will become seedy over time. ( looks like tiny specks of sand are in your paint ) I'm just not sure if it happens to an unopened can or if air is the cause.

 

[teletech]

Teltech is correct, read the data sheet. If you use the DP- 401 activator there is an induction period that must be adhered to. If you use the quicker -402 activator there is no induction time.
Think i will check to see what's left on ebay. Only thing to keep in mind is that epoxy will become seedy over time. ( looks like tiny specks of sand are in your paint ) I'm just not sure if it happens to an unopened can or if air is the cause.

I've found the DPLF flows *much* better with that optional acetone in the mix, I don't even use the full 1/2 part but just a splash seems to help a lot.
The stuff I got was 44GN011 Water Reducible Epoxy Primer and only about 1 month expired.
It's water-reducible so I'm not totally sold on using it on bare steel, but over paint it's perfect.
In my case I have an aluminum hull I've been prepping and had been gritting my teeth preparing for what a couple gallons of aluminum compatible primer was going to cost me. So... win! It's odd to mix and follow the instructions but otherwise I've been using it for all sorts of things with good results.
I also bought some of the Desothane HS CA8100 Anti-Chafe Topcoat which has been very cool, comes in a light gray and thus far has been great, chemical resistant and stuff just wipes off. It's miserable to sand though, not surprising since it's full of PTFE!

For those unaware, all PPG paints have a P-sheet, the technical instructions for use of the product and well worth the brief time to download and read! It's also the case the Anest Iwata and perhaps others have actually gone to the effort to produce spraying guidelines for common finishing products with their equipment, also very helpful in setting up to spray if you haven't used a product before.

 

[01GRANDER]

I do mostly high end automotive restoration work, but I have also painted everything from excavators to military equipment and everything in between. My current personal preferance is a 2 part epoxy primer. It will adhere very well to everything including bare steel with no adverse reactions to other previous paints. It is also the most moisture resistant of all the primers available, thus providing the best long term corrosion protection. You can top coat it wet on wet or it also has a 1 week recoat time without the need to scuff or sand, unlike the narrow 24 hr. window of a 2K urethane primer between sanding and top coating.
I like PPG's DPLF line but it is fairly pricey. You can get their Omni line much cheaper. I have also used 5 Star which is a good economy epoxy.
This is assuming you want just a primer or primer / sealer. The epoxy in my opinion it too hard to use as a primer / filler if you are trying to prime and sand to remove imperfections. For this I would use epoxy as the barrier base layer, then 2K urethane over that for you sandable layer. After wet sanding the urethane I would use the epoxy again in a 4/2/2 mix as a wet on wet sealer before your final topcoat.
This might be a bit overkill depending on what you are painting and your desired outcome, but it will last a LONG time.

So I don’t mean to sound like I’m disregarding your info, it’s actually good to know for future projects but what would be the easiest way to paint over Carc with a 1 stage? Do I need to use a primer or would roughing it up be just fine? I know most people just rough it up to spray Carc again but obviously a 1 stage urethane is different

I plan on taking my Hmmwv off-road a lot so I am not as concerned with a really good paint job, I know that can sometimes bite you in the rear but I think a sufficient 1 stage from a quality paint line would suffice for my purposes.

My ultimate goal is to get a C2 corvette and I’ll definitely heed your advice on that one.

 

[glcaines]

I have painted several military vehicles and trailers with Gillespie 383 green. I have put it directly on top of the CARC. Even more than 10 years later, I haven't had a problem with pealing or anything else. The only place I've used primer is where I've encountered rust. I remove as much rust as I can and prime with Rustoleum rusty metal primer. I then put the Gillespie on directly over the Rustoleum without waiting. Again, no problems.

 

[01GRANDER]

I have painted several military vehicles and trailers with Gillespie 383 green. I have put it directly on top of the CARC. Even more than 10 years later, I haven't had a problem with pealing or anything else. The only place I've used primer is where I've encountered rust. I remove as much rust as I can and prime with Rustoleum rusty metal primer. I then put the Gillespie on directly over the Rustoleum without waiting. Again, no problems.

But isn’t Gillespie supposed to be a kind of non-official Carc? I was told by someone else a 1 stage urethane would probably be good for a few years and then start to have issues, peeling and cracking due to it being chemical resistant, including urethane.

 

[glcaines]

But isn’t Gillespie supposed to be a kind of non-official Carc? I was told by someone else a 1 stage urethane would probably be good for a few years and then start to have issues, peeling and cracking due to it being chemical resistant, including urethane.

Gillespie paint is not CARC. It is a CARC substitute that matches the color of CARC very closely. It holds up very well in my experience. As far as urethane paint goes, airplanes are painted with urethane paint and they don't seem to have a problem. I repainted my Cessna 152 years ago with red urethane paint and it still looks very good, although I have now sold it.

 

[01GRANDER]

Gillespie paint is not CARC. It is a CARC substitute that matches the color of CARC very closely. It holds up very well in my experience. As far as urethane paint goes, airplanes are painted with urethane paint and they don't seem to have a problem. I repainted my Cessna 152 years ago with red urethane paint and it still looks very good, although I have now sold it.

Yes but someone said Urethane has an issue over Carc so I’m trying to find a primer to go directly over Carc that would work and not cause issues 1-3 years from now.

 

[01GRANDER]

Gillespie paint is not CARC. It is a CARC substitute that matches the color of CARC very closely. It holds up very well in my experience. As far as urethane paint goes, airplanes are painted with urethane paint and they don't seem to have a problem. I repainted my Cessna 152 years ago with red urethane paint and it still looks very good, although I have now sold it.

Someone suggested using an epoxy primer and then putting the urethane on top. Would an epoxy primer bond to Carc?

 

[Ray70]

Anything is going to bond to the CARC as long as it is in good sturdy condition, clean, sanded and not peeling or anything.
Once any type of paint is fully cured, the next paint job bonds mechanically not chemically. Paints only bond chemically before their recoat time has elapsed, ( such as when spraying "Wet on wet" with sealer / primer then topcoating right away), which is typically a few hours for most paints and up to a week for epoxy. after the recoat time you have to mechanically sand the previous paint or primer so that the new paint has some tooth to grab on to.
The only thing you need to be concerned with is a reaction between the new paint and the old where the solvents in the new attack the old and cause it to soften up and wrinkle up, loosing its bond to the layer below, since CARC is chemically resistant an adverse reaction is pretty much never going to happen.
Once you start applying the urethane, just mind the recoat times listed in the data sheet. In many cases you can not wait more than 1 hour between coats or you get into the time frame where the 2nd coat attacks the already curing first coat and causes it to crinkle.
1 note on sanding CARC, its bad stuff so wear a respirator and use ventilation. It is also very hard paint so plan to use a lot of sanding discs and change the disc often as they will dull very fast!

 

[01GRANDER]

Anything is going to bond to the CARC as long as it is in good sturdy condition, clean, sanded and not peeling or anything.
Once any type of paint is fully cured, the next paint job bonds mechanically not chemically. Paints only bond chemically before their recoat time has elapsed, ( such as when spraying "Wet on wet" with sealer / primer then topcoating right away), which is typically a few hours for most paints and up to a week for epoxy. after the recoat time you have to mechanically sand the previous paint or primer so that the new paint has some tooth to grab on to.
The only thing you need to be concerned with is a reaction between the new paint and the old where the solvents in the new attack the old and cause it to soften up and wrinkle up, loosing its bond to the layer below, since CARC is chemically resistant an adverse reaction is pretty much never going to happen.
Once you start applying the urethane, just mind the recoat times listed in the data sheet. In many cases you can not wait more than 1 hour between coats or you get into the time frame where the 2nd coat attacks the already curing first coat and causes it to crinkle.
1 note on sanding CARC, its bad stuff so wear a respirator and use ventilation. It is also very hard paint so plan to use a lot of sanding discs and change the disc often as they will dull very fast!

Thanks, that’s great info, I never knew that. I actually ended up buying a 2 part epoxy primer from Speedokote, they got me with the Trex picture.

 

[Jones]

Ray70 hit the nail on the head.
Be very careful when sanding or grinding on CARC. It's loaded with nasties like ground quartz, feldspar and stuff I can't even pronounce. N95 Respirators, not just dust masks to protect your lungs. Goggles to protect your eyes. Capturing the dust and / or vacuuming up afterwards is a must.

 

[mzak88]

Ray70 hit the nail on the head.
Be very careful when sanding or grinding on CARC. It's loaded with nasties like ground quartz, feldspar and stuff I can't even pronounce. N95 Respirators, not just dust masks to protect your lungs. Goggles to protect your eyes. Capturing the dust and / or vacuuming up afterwards is a must.

Wet sanding be an option?

 

[teletech]

Ray70 hit the nail on the head.
Be very careful when sanding or grinding on CARC. It's loaded with nasties like ground quartz, feldspar and stuff I can't even pronounce. N95 Respirators, not just dust masks to protect your lungs. Goggles to protect your eyes. Capturing the dust and / or vacuuming up afterwards is a must.

Quartz and feldspar aren't particularly nasty, they are just what granite is made of. Very inert and harmless unless you manage to grind them up so very finely that they are respirable. Almost anything that isn't water-soluble (and a lot of things that are) get nasty at those sizes. You *might* get them that fine when making the paint but they are mostly not going to be that fine when you grind or chip the paint off. There could well be "other nasties" in CARC that you would NOT want the breathe regardless of size, I don't know.
Obviously with any grinding operation it's important to wear proper PPE but applying CARC is much more dangerous than removing it.

 

[thoner7]

I’d like to get some clarification on sanding carc for repaint.

would a good dust mask from Lowes or HD work? Like the kind that take filters for drywall ???(drywall dust is real fine and usually yourvacuum needs a heppa filter to filter it out)

also since the only place I have to sand this thing is my driveway- where my kids play- do you have to worry about the paint dust like you would lead paint for example?

 

[01GRANDER]

I’m using this mask and filter cartridge. Hopefully it’s sufficient.

 

[87cr250r]

As I understand, the risk from CARC is the silica content. Silica is not harmful when ingested so it is not like lead. If it's on the ground it's ok.

It is bad if inhaled.

So you have two options, wear a respirator or don't make dust. Wet sanding means no dust and makes your paper last longer.

On that note you should vacuum the ground when you can because the residue will eventually dry out and become airborne.

If you must dry sand one of the 95 and above respirators should work depending on the permissible exposure limit.

Urethane paints are a problem, too. They have isocyanates in them which are moisture reactive. If you are working with urethane paints you must use respirators for organic vapors. If you're spraying, protect your eyes too. The urethane paint systems cure by moisture and will stick to your mucus membranes.

 

[thoner7]

I’m using this mask and filter cartridge. Hopefully it’s sufficient.

I went with something similar. P100 for dust and also rated for organic compounds. Figured it would help if I spray anything but I also do a lot of wood finishing so it’ll be dual use.

now if only I had someone else’s parking lot to do my sanding in lol!!