View Full Version : Mixing hardners and urethanes and getting away w/ it...debunking myths

02-01-2007, 04:51 PM
I've heard the admonitions of trying to be a "junior chemist", and not to intermix the proprietary ingredients in canned paint items within or across paint manufacturers lines...but all that aside, can anyone give a solid reason, through user experience as to why it would or wouldn't work.

Specifically, is the use of urethane hardeners in urethane clears.

I know the final product is a manufacturers best blend for a tested and intended use, but what's to say that mixing in some other products, labeled differently (and less costly) wouldn't still promote cross-linking and a predictably durable finish.

I do realize, if you're shooting cars for a living, moving a lot of product frequently, or in the business of marketing and selling paint, then one is probably not that concerned about what else might work, especially for the little guy that's only using a fraction of the smallest cans at a time...and taking a long time to do so. As such, that's the situation I find myself in...many different products, clears, primers, hardeners and reducers...some w/in various manufacturer paint lines, some across lines...how "unique" is this stuff...anybody else have the inclinantion to experiment to see what "leftovers" will react favorably?

It all started when I needed a hardener for an obsolete clear (w/ little forthcoming info). I located a suitable substitute, that worked across several lines...just couldn't find it in stock anywhere. So I contacted some jobbers, that made it a matter of practice of not offering any "universal" additives for anything they sold. So I pressed further, contacted a paint representative, who, in addition to telling me where I could find the hardener in question, also mentioned the fact that I could use any high quality hardener within the paint line and they would all work satisfactorily...well, that was good to know...yet I was still skeptical since it goes against the common wisdom of play it safe and spend another $50/qt for hardener that will likely have the greater portion sit and go to waste.

So, and I'm not advocating any use practices here...just trying to appeal to chemists or product users to understand what's real science, theory, or actual world experiences.

I deferred my questions to a neighbor (a retired chemist who has patents on a few epoxys, has knowledge of urethanes, and worked as an adhesives specialist for Johnson and Johnson), so seemed like he has a more than rudimentary inderstanding of what works.

The condensed version of my inquiries, was that basically all the urethane hardeners will promote cross-linking, just some at different rates (and some rates that are more easily modified by the thinners/reducers...which are also basically interchangeable).

In understanding things correctly, the thinners themselves, so long as they evaporate (and all they're really doing is altering viscosity) and evaporate completely, they leave the substrate leaving the solids behind, and you could just as well use a great variety of things to reduce urethanes and enamels (be it lacquer thinner, MEK, gasoline, etc etc.) w/ no ill effects on film durability or dieback...you just have to be willing to do the experimentation in the first place (and this thinning out, taking presence in a urethane that's cross-linked, would not have the same strength diminishing properties you'd experience w/ using a solvent rather than reactive diluent in an epoxy).

Also asked about the deal on shelf-life of hardeners...standard across the industry on can labels seems to be, 1 year unopened, 2 weeks after opening...mine last longer, why? Hardeners react to the moisture, I get that, it's always present to some degree (some hardeners I squirt a bit of Argon/CO2 in the can before sealing, and for a long time prior, I did not)...the moisture cured urethanes that I've played w/ over the years (POR, RB, etc.) all stayed liquid for a good long time as well when resealing the can w/ some attention. So, it'd seem, so long as you minimize the hardener's exposure to moisture and or/air, then they should last indefinately...there's nothing else really going on in the can, unless you have moisture (they don't rot/degrade...they either slowly harden and react, forming a skin, seeds, or final gelation...or they don't).

So just trying to see if someone else has done the same as I am about to do, before heading out to put another can of hardener on the shelf, along w/ the 5 other pints/quarts from different brands (DuPont, Standox...etc.).

Basically, I'm spraying out less than 15 square feet at any one time (or less) w/ a tinted clear...if it fails, the hope is that it will be obvious and in the short term, so I can redo (these are for something added on my surfboards). But, if chemistry serves right, the hardener/catalyst will kick, the reaction will be complete, and that's about the end of the story.

02-01-2007, 05:30 PM
its basically like this, the most urethanes are all essentially the same. theyve got pigment, binders, resin, etc, just as most hardeners contain the same ingredients and perform the same actions(cross linking, as you already know) and most reducers do jsut that, reduce the paint, and they all basically have the same ingredients. most of the hardeners and stuff that paint companies sell with their name on, all come from the same manufacturing plant and they jsut have different labels put on them. so your thinking right now, well hey if theyre all the same, why not mix them together.... the problem with playing "junior chemist" is that each company has their own concentrations of all the ingredients. company A's clear might require 30% of a particular ingredient that is only found in that concentration in company A's hardener, and you add a hardener from company B that has 50% of that same ingredient. the result could go a bunch of different ways depending on the ingredient. the clear could over harden, making it brittle, or it wouldnt harden righ and stay soft and somewhat dull, or it would work perfectly. the same thing goes with reducers, and this one ive witnessed myself, i was spraying some single stage urethane from dupont, and i couldnt find my open can of reducer, so i used some ppg reducer instead. it thinned it out fine, but it thinned a LOT quicker than the dupont stuff did, so i had to be careful and watch my viscosity. it sprayed fine, and is still holding up but its really risky. if you thin it up too much, youll be wasting a lot of paint trying to get the right viscosity. overall, id say if you wanted to experiment a little, go right ahead just dont make a habbit out of it as it is definately a very very risky idea...


02-01-2007, 06:05 PM
Thanks, that was a fair enough response...my main reason for wanting to see if what I had on hand would catalyze my clear, is because I wanted to experiment in small amounts, just how much tint/opaque/pearl flake/various dispersions to add in what ratio to get a variety of effects.

I figured using the clear on hand would be the economical route to test out the proportions of colorant additives.

Any suggestions as to where to start on a percentage basis for dry additives (like pearlescents or powder pigments)? I also have a host of translucent as well as fairly concentrated opaque colorants, petroleum based so I'm hoping for compatability (should have any sort of epoxy or polyester as a suspension agent)...labeling says it's compatible w/ urethanes, although it cost much less than a urethane dispersion.

I figure I'll be mixing up a 1/2 ounce at a time to shoot on the boards.