Epoxy primer for cold temperatures

[duffman]

Hi I'm currently doing a car restoration project. I'm cutting out panels to get to rust then welding the original panels back on again in places. Just looking to put a good coat of paint on the inside of these panels. However I'm worried now if I paint on some 2 pack epoxy primer it might not cure as I'm working out of a cold shed that's not insulated. I can heat up the panels with a heat gun prior to paint and put a gas heater on as well, but overnight then temperature will drop to 0 degrees.

Is there a good primer that will cure even at colder temperatures? Any one used any with good results?

Many thanks.

 

[julianf]

I keep epoxy (not primer, but other epoxies) in the freezer, post mixing, to slow their cure.

It works for a while, but they all still go hard eventually.

 

[jo1010]

Your right to worry about it. Practical min temp is around 13C and most say room temp (18-20C). IR heaters (or even oil filled electric heaters) are the way to fully cure, and leave them on until cured. I wouldn't use gas bc of introducing more moisture.....on the insides of panels there are industrial (non-automotive) low temp primers around (with a fast hardener) but I've not used them...

 

[Misterg]

Is there a good primer that will cure even at colder temperatures?

Also interested in this. I've been using Lechler 107, but the TDS says it needs 48 hours @ 20°C for a full cure, and to avoid cure at <15°C.

My gut feel is that all epoxies will cure eventually, but even I'm reluctant to rely on that for something that will be inaccessible. For larger areas and special occasions, I can heat my shed to 20° if it's not too cold outside, but this isn't really practical for odd bits and pieces, so I've done some with conventional, zinc-rich primer.

I'm using the Jotmastic 90 on the underside of the car, and I'm considering using it to brush on to the insides of repairs. The TDS says 5°C for standard hardener or -5° for their Winter grade hardener. It's a bit gloopy, though. I'm not sure whether it would be an option for you, as I don't think you can get it in less than 5L at a time.

I keep epoxy (not primer, but other epoxies) in the freezer, post mixing, to slow their cure.

Out of curiosity: How long can you store them for? (hours / days / weeks?)

 

[steveo3002]

jotun does winter hardener

heat gun the panel and warm it over ive never had it fail to go off

 

[Dcal]

There are primers that will cure at lower temperatures but epoxies are probably the most user friendly and readily available primers for your application.

It's worth a trawl through the paint section on this forum as this has been discussed before but it's hard to go wrong with epoxies.
As @jo1010 has already said infrared heaters are your friend for drying any 2 part paint, however the real problem with low temperatures is the viscosity.

Cold temps make it thick and harder (but not impossible) to apply. Heating the mixed paint is a big help but if the panels are not heated as well it cools as soon as it touches the metal (still helps though)

For the underside I'd recommend an epoxy mastic with added aluminium, something like Jotamadstic 90A with winter grade hardener and some thinner 17 to ease flow.
But there are loads of similar products.

Epoxy mastics are remarkable products and hard to mess up.
Most can be applied in cold damp conditions and some (like interzone 954) will cure when immersed in sea water 30min after application.
However good prep will improve the performance of any paint system so don't scrimp on that.

 

[julianf]

Out of curiosity: How long can you store them for? (hours / days / weeks?)

I use other epoxy based products. Deep pour resin and also the ink that I use for printing is epoxy chemistry.

The deep pour resin is days. Maybe even a week. At -18c.

The catalyst in the ink is not normal. It's got other adhesion promoters in there. I have used it for print the next day but only once.

 

[GRW]

I used Jotun 90 a few weeks ago to overprint my sill & jacking point repairs (I also used some Bilt Hamber weld-through primer).

Warmer than right now for sure, but in the day I'd think 10-degrees tops, and of course less overnight.

Everything still seems to have cured no problem (though I expect it took longer, but my van wasn't moved for a week).

(I also had some rain within a short period of applying 90 to the sills - even though no way had the paint cured, the rainwater just sheeted off it with no apparent ill effects to the Jotun.
(Not a scientific nor a test I wanted - but good that it seemed to shrug it off).

 

[duffman]

I've got

There are primers that will cure at lower temperatures but epoxies are probably the most user friendly and readily available primers for your application.

It's worth a trawl through the paint section on this forum as this has been discussed before but it's hard to go wrong with epoxies.
As @jo1010 has already said infrared heaters are your friend for drying any 2 part paint, however the real problem with low temperatures is the viscosity.

Cold temps make it thick and harder (but not impossible) to apply. Heating the mixed paint is a big help but if the panels are not heated as well it cools as soon as it touches the metal (still helps though)

For the underside I'd recommend an epoxy mastic with added aluminium, something like Jotamadstic 90A with winter grade hardener and some thinner 17 to ease flow.
But there are loads of similar products.

Epoxy mastics are remarkable products and hard to mess up.
Most can be applied in cold damp conditions and some (like interzone 954) will cure when immersed in sea water 30min after application.
However good prep will improve the performance of any paint system so don't scrimp on that.

I've got some epoxy mastic from rust buster I bought two years ago. I think it might work ok. Is the epoxy mastic better than epoxy primer?

 

[Dcal]

For the underside certainly.
The finish might not be great but the performance is in another league.

The rust buster epoxy might even be re-packaged Jotamastic

 

[duffman]

For the underside certainly.
The finish might not be great but the performance is in another league.

The rust buster epoxy might even be re-packaged Jotamastic

Yeah I read that it's just it rebranded as rust busters. Temperatures are on the rise for next week so going to buy an infra red heat lamp and get these bits painted. I've used phosphoric acid on it but need to do another few passes with the wire wheel and few more coats of acid.

 

[Dcal]

Wire wheel is ok for removing heavy rust but finish off with sanding.
80 or 100 grit will leave a good surface for epoxy mastic.

 

[duffman]

Wire wheel is ok for removing heavy rust but finish off with sanding.
80 or 100 grit will leave a good surface for epoxy mastic.

I was using a small belt sander and a few wire wheel drill attachments. I've a mbx bristle blaster maybe try that tomorrow although it's a bit big.

 

[ajlelectronics]

I was using a small belt sander and a few wire wheel drill attachments. I've a mbx bristle blaster maybe try that tomorrow although it's a bit big.

Wire wheels polish the surface making it too smooth for epoxy, hence the advice above from @Dcal .

 

[duffman]

Wire wheels polish the surface making it too smooth for epoxy, hence the advice above from @Dcal .

Yeah I understood that. Wire wheels were just used to remove the rust. I will scuff the whole surface prior to paint.

 

[Dcal]

If you have the Bristle Blaster with an accelerator bar it's the best hand, bar none, for prepping steel for paint.

The accelerator bar flicks the wire brush needles to create a micro divit which is just what you want.

 

[charlysays]

SML paints do a marine Epoxy primer surfacer which is rated to cure down to 5c. This is about the coldest I've seen for a sandable spray able epoxy primer.
MIPA grundierfiller EP fast cures down to 10c. That's about it for primer surfacers.
Epoxy mastics like jotamastic will cure at -5 or even colder with winter grade hardener but aren't very sandable and not especially easy to spray.

You are right to be concerned as epoxies are naturally slow curing which makes use of heat lamps prolonged and not very practical. I've had lechler and hb body epoxy take days to harden up in average autumn weather (10c at night, warmer in day). I think a more cold tolerant product like jotamastic or a marine primer surfacer like the sml stuff is the best bet in a cold shed.

 

[Dcal]

If Jotamastic is fully cured it's not bad to sand.
Certainly not 2k primer sanadable but ok.

When it's not fully cured it balls up and clogs the paper.

I've used it a a spray filler when filling heavy pitting in body panels, my reasoning is if the pits are filled with a product designed to resist corrosion it as much as I can do without cutting out metal.

 

[duffman]

If you have the Bristle Blaster with an accelerator bar it's the best hand, bar none, for prepping steel for paint.

The accelerator bar flicks the wire brush needles to create a micro divit which is just what you want.

I need to get an accelerator bar for it. It is a good job, but not designed for these right spaces. Very slow on really heavy pitting only thing I've seen fully remove it is blasting. The dust goes everywhere from the media breaking down, is the only downside, so I'm not using that.

 

[Dcal]

Spot blasting with a recirculating gun works surprisingly well on small areas.

Blasting is the best prep but does have lots of drawbacks.