Somewhat ot but I just primered my 1947 Oliver model 70 tractor using epoxy primer. (Light gray) Now this is a little new to me, I've done polyurethane clear coat before but not epoxy and I'm not much of a painter and hideous on the prep work. But the question isn't about that it is about the hardener so I hope someone knows the answer.
What happens if you only use half the recommended quantity of catalyst? Now as for speculation, I can do that about as well as anybody else. And since it is epoxy based my guess is that it will catalyze at a reduced rate and take longer to reach full hardness. But does anyone know for sure?
I discovered my error while mixing the second quart and other than reducing the quantity from a quart and a half to a quart and eight ounces it sprayed the same and dried the same as far as I could tell. I'll check it again after the weekend but I doubt it'll cause any problem. I'm just curious. Hey, it's a tractor right? It doesn't have to be show quality. Once it is all green, red, and yellow and the decals are on nobody will care about the primer.
Jim
A call to the mfr would probably get you a better answer than asking here. I would hate to assume everything is good and lose the paint job later on - what with the cost of paint these days.
Jim, unfortunately your primer will never harden, epoxy systems rely on accurate measurement of resin to hardener
,with the laminating resins we use they will tolerate up to 5% error,. People often confuse catalyst ratios because polyester and vinyl esters use an MEK catalyst its called free radical catalysis, the chemicals search for open sites with which to link catalyst ratios can vary from 1.25 to 5% depending on the temperature in the shop.
Epoxies create a chain of links, that is why they are so stiff compared to poly and vinyl esters. Most epoxies have different hardners to speed up or slow down polymerization, so I think for an epoxy primer or paint there should be adequate working time
for the application, most two part( resins, paints etc.) are predicated at 77f in quantities, over 77f polimerization is exponential,lol.
Dave
Thanks, that coincides pretty well with what I (think)I know. Epoxy primer seems to be a different bird due to the organic solvents used to make it sprayable. My dad actually helped develop epoxies as a lab worker for Union Carbide but I'm not all that familiar with the chemical intricacies. The stuff did dry to touch, and quicker than I expected. I used that quart for back sides mainly: under the hood, back of the dash and such.I did notice that it dried with a flat finish where the correct mix ended up semi-gloss and I suspect as noted it will not be as hard. But Friday it felt as hard as conventional primer so I doubt the color coat will peel off. (Acrylic enamel, about $80/gal.) I'll go look at it again in a bit. One thing I've noticed about epoxies is that the hardener ratio is often a bit more flexible than the documentation would have you believe and sometimes something as simple as accidentally switching caps will make all the resin set up. Maybe not with the same physical properties but enough to make it all get hard, and it might take weeks instead of minutes. That may be what I'm seeing here. No doubt it won't reach full hardness but it looks to me like it will be plenty hard enough to hold the color coat. But now that it has sat for a couple days I'm pretty curious to see how it looks.
Jim
Epoxy paints WILL dry without the catalyst. It just takes longer. However, it will not be as tough or hard as a surface that was catalysed.
I painted the frame on my 1952 LandRover by brush, with non-catalysed green epoxy paint some 15 years ago. Still on there and still green. And I do not baby the LandRover (e.g. It's in the bush, bashing through brush and rocks, as often as I can take the time to get there).
M.
Martin , was the hardner inadvertantly left out,, or was this a paint that required no hardner ?
Dave
I picked up the color paint today and will use a hardener in it. (Acrylic enamel). My older brother claims the hardener is the same stuff that super-glue is made out of. Anyone heard that one?
Jim
Dave,
The paint was Dupont #38500 (LR Bronze Green), Hardener 77-S, Thinner 8508. I was advised by the paint store not to use the hardener if I was brushing it onto the frame, as it would set too fast.
I used the hardener for painting the panels, but left it off for the frame. Seems to be fine. It dried in about an hour and has been fine now for 15 yrs.
Martin
Yeah, epoxy paint is kinda weird stuff. Take floor paint for instance. Apparently there is a version with 100% solids but the more common version uses a solvent and does not get particularly hard. Still a lot to learn in that area.
Jim
Well I wouldn't advise anyone painting their car NOT to do as the manufacturer has stated, it is a plural component system and a stable base is what you're looking for before putting a lot of expensive primers and paints over it. I suspect the paint store suggested not putting hardner in the mix to give you pot life, if you mix smaller batches with hardner you would have adequate time to brush paint the chassis , we use DP90 for certain jobs and it sprays excellent and if sanded through touched up by brush.
We use it for rust protection where metals get bonded in to the substrate.
Dave
Yeah I wouldn't advise it either, you could just as easily end up with a gooey mess on your hands that never cures. Some of that stuff can undoubtedly be real critical of the ratios and in development I think they had some real problems getting a workable pot life to go with a realistic cure time so it might be real easy to accidentally revert to those old problems. In this case and in Martin's it seems to have worked out OK though. I don't think spraying the catalyst over the sprayed semi-catalyzed resin would have proven a very good solution.
Another thing I've noticed though. You know how epoxy glue gets warm and kicks off when it cures? With catalyzed paints that doesn't seem to happen. If it did you would have to completely and thoroughly clean everything and start over with each new small batch but instead you can mix in fresh resin and catalyst with no ill effects. Probably a result of the extended pot life.
Jim
One major item you've forgotten is adhesion. Epoxy requires the correct mixing not only for a set rate but also the adhesion factor.
The same is true for powder. If not fully thermally cured it will look fine (even a little shiner than fully cured paint) but when impacted it will crack and delaminate! The same is true for liquid two component paints like epoxy primers
I have an industrial finishing company and deal with these type of issues on a regular basis
One additional note:
There are two reasons to paint something. The first is functional i.e. protect the surface, the second is decorative.
Epoxy is used as a primer and out of the sun's exposure applications because of "tightness" of the film! Paint is a semi permeable membrain which allows oxygen to pass through it after some period of time. Again, the quality of a coating is determined by the tightness of the film!
When epoxy cures (chemically cross-links) it develops a very tight film to help stop the transmission of oxygen through the paint film. Florida exposure testing shows epoxy will outlast polyester alkyds by a factor of 5.
The only reason epoxy is not used on exterior (decorative) applications is the resin type is very suseptible to UV (ultra-violet) degradation. In other words the sun will chalk the surface and fade the pigments in the paint very quickly.
Short of E-coat, epoxy resins are the very best for base coats on ferrous (steel) surfaces!! When you extend pot life through improper mixing you're sacrificing long term performance for longer pot life - a trade I wouldn't make!! Mix smaller batches and cover small portions at a time.
A different blend perhaps ? I have used rattle can epoxy paints, from Home Depot, and they held up excellent on steel and aluminum, out doors,(years). roverman.
How can a rattle can paint possibly be epoxy? Seems like it would set up in the can or come out in clumps.
Jim
Have you ever used epoxy glues? Identical methodology!!! There are no single component epoxy glues.
The cross linking is what gives epoxy its strength. Epoxy paint doesn't lose its functional strength in sunlight but it will definitely chalk and lose its color!!
Art, I can't tell you much about the rattle can epoxy paint you have without reading what it's made with so I won't speculate! The first thing that tells me somethings amiss is that the paint didn't chalk during its outdoor exposure.
Thank you Doug !! real epoxy is a plural component system.
Dave