Paint Hardeners

PeteVS

PeteVS

Well-known member
How critical is it to use the appropriate same manufacturer hardener with paint? I have some paint that I bought locally (expensive) a few years ago and now I have to repair some damage to one of the parts I used it on. I found the paint but I haven't located the hardener. I do have some paint (different colors) and hardener that I bought recently and I was wondering if I can use the new hardener with the older different brand paint. Is getting the exact proper amount of hardener critical? Thanks for any comments!
 
I would not think to use a product I was not 100% certain was compatible with the paint. Too many possible terrible outcomes.

If the paint is a brand name, you should be able to find a supplier of that brand and ask them what they mix it with.

The exact amount critical? What do you mean by critical?
I'm a tad retentive so I mix as exact as humanly possible.
 
I agree 100% with what Kobe has indicated. I used PPG Concept on both of my restorations and PPG has eliminated the product. I have various quantities of the paint
left so I plan on sourcing the correct hardener on Ebay as my local supplier no longer
offers any products associated with Concept.

Peter
 
Keep the hardener in a small refrigerator. The paint part does not go bad on a shelf but the hardener eventually does loose its effectiveness. Cold storage slows the degradation significantly and as a bonus then you will know where all your hardeners (including body filler, epoxy ect.) are at all times. Old stock hardener from eBay is thus a **** shoot. I'd rather use some other companies new urethane hardener than old urethane hardener that has been in a hot garage for 10 years.


To test paint viability simply mix up a few grams sample on a mini-scale and brush/spray it out and see if it hardens or stays sticky.


The amount of hardener does not need to be to the gram exact put pretty darn close for most modern paint. Think of it this way, neither paint nor hardener sets up alone. If you have too much of either it is left as an uncatalyzed liquid trapped in a sold shell making for microscopic wet spots that never dry. A few microscopic spots trapped in the matrix here and there is probably not a problem, when half the paint job is not catalyzed you got soft paint issues.
 
You dont have to use a hardener in most paints . Its an optional additive that can make the paint dry a little faster and dencer while giving it a little more shine along the way. Thats why the counter guy asks if you want it. So if you cant find the corect one I wouldn't worry to much. Tim
 
I just went through the same issue when I wanted to use up some PPG DAR acrylic enamel but the recommended hardener is no longer made. I found some ProForm 2.1 VOC Universal Urethane Hardener (it may be called something different in USA) and it worked well with the enamel and also with PPG JTX Direct Gloss Acrylic Urethane. https://proformproducts.com/us/en/pro-form/ After the fact I received this from PPG customer support when I had asked about using another low VOC hardener that I had on hand:


"We would not recommend this; you should not mix modern urethane hardeners like JH6028 with an older acrylic polyurethane enamel like PPG's Delstar DAR. DAR was formulated to be catalyzed specifically by old-style enamel hardeners (such as DXR80), whereas JH6028 is a specific isocyanate-based converter/activator intended for acrylic urethane systems like JTX. Crossing chemical families and generations risks severe solvent boiling, wrinkling, mapping, or a complete failure to cure properly.

DAR components are entirely obsolete. Since original DAR components are completely gone, you cannot safely use the leftover DAR paint. Trying to force modern JTX activators into old enamel will cause the paint to wrinkle, stay sticky, or lift off the car."
 
I watched a You-Tuber video the other day where a guy wanted to paint the underside of the engine hood and have it dry in very short time so he could flip it and paint the other side the same day.

He was using 2 stage product for the base color and adding clear coat with fast dry thinner (reducer?) and hardener for a poor mans single stage. It worked for him but he also added that he didn't recommend this for the overall top coat. It was just for the unseen elements of the body.

Mixing chemicals that may not be compatible can result in all sorts of surface maladies like curdling or wrinkle finish. If both products are for similar chemicals then it can work but using acrylic product with polyester product may not. If the base color is a polyurethane then find a polyurethane hardener. Same with reducers or thinners. Compatibility is everything when trying to do stuff like this.
 
Rotorwrench:
Thanks for the heads up on polyurethane and acrylic products! I'll have to see what I have with the stuff I recently bought.
 
Also, adding less or more curing agent can result in uncured, sticky finish, or a frothy, porous finish.
 
I just found the hardener for the paint I wanted to use. The hardener had hardened into a lump a bit bigger than a golf ball in the can. I wound up using my new paint and hardener but it didn't come out as nicely as the original stuff. (It's gotta be my fault...)
 
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