Considering 2k Polyurethane Finishes

A long and thoughtful discussion on the virtues and drawbacks of two-component urethane finishes. October 2, 2005

I'm curious about 2k urethanes. It seems like they might work well for my application, which involves wood and metal coating. I've been experimenting a bit with waterbornes, but I'm not sure if they will cut it - they seem a bit soft. I like the fact that the 2K's don't have a build limit to them (we do full, rubbed out, glassy finishes) and can go over wood and metal substrates. Are they much more toxic than CV? I have used CV plenty and like it, but can't work within the build limits. I'm wondering if the 2k is the 'next level' beyond the CV.

Another thing is availability - my SW chemical coatings outlet does not carry their line of 2Ks. I can get some from some body shop supply places, but should I be wary about using products that are designed for cars on wood? The thing I liked about the spec sheet on the SW product is that it specifically stated that it was for wood, plastic, and metal.

Forum Responses
(Finishing Forum)
From contributor M:
ILVA's 2k urethane is very low in isocyanates. I do not know about the others on the market. I do know they are a great finish for wood or metal applications. I have a high gloss white kitchen and a round bar table that is holding up to a 10 year old jumping and kicking her way to every glass or dish she needs (about every 10 minutes!). The table has also held up to all her homework, ink and markers.

From contributor C:
Don't jump right in; you really need to do your homework. These coatings are not for everyone, so you need to know what you're getting into.

From contributor M:
I do agree about doing your homework, but in my experience with customers who have used CVs, they have no problem using the 2Ks. Follow the product data sheets and you'll find it very user friendly.

From contributor H:
The catalyst used in most 2k urethanes is isocyanate based and that is some nasty stuff. I personally don't give a crap how much of the stuff is in there. If you decide to spray, I would get nothing less than a pressure feed fresh air breathing system.

Why not consider an acid based post cat system? Do you really need the protection of a 2k urethane? I am not saying they are not worth it, but do you really need it?

From the original questioner:
I like the idea of a less toxic product (why I tried waterbornes), but I have to have the performance there. My spray setup is low tech, in a good room with ventilation and a respirator, but no moon suit or anything. CV, precats, waterbornes, nitro have all worked well. I'm familiar with mixing catalysts and pot lifes. What sort of a solvent do you use with 2Ks? Sounds like this stuff could be the all-purpose clear I have been looking for.

I have used acid cat/post cat stuff. All have build limits which are restrictive. Either that, or they are too soft and rubbery to be durable.

From contributor H:
I guess you and I are not building cabinets on a Saturday afternoon. I would use acetone as a solvent because it is an exempt solvent versus mek. How many dry mills are you trying to hang? I am not questioning your thoughts or abilities, but the post cat is rubbery?

From the original questioner:
It's a balancing act. I need the coating to be flexible so it won't crack, but I can't have it too soft. I had a precat once which had no build limits, but it was too soft, had poor print resistance, and didn't rub well. The post cat (acid cat) I tried was great, and pretty tough. But it would crack if you built it too high. The waterborne was good but still a little soft, and didn't rub out easily. I need a total of around 10 mils dry for a good finish. Our goal is piano-like. Since we also finish metal parts, it would be nice to have a proper clear to go over them as well. That is one reason I am being drawn to the 2Ks as an all purpose clear. I have used CV for this purpose, but it's not really designed for this application.

From contributor S:
Some 2k urethanes have dry mil thickness limits. Didn't I read that you are limited to 10 dry mils with Milesi? If I had to trade the exposure to the low isocyanates found in today's popular 2k urethanes with the use of xylene needed in conversion varnish, I certainly would. With a decent spray booth/ventilation and a maintained/fresh cartridge respirator, you are safe. Be safer and do not wear shorts or short sleeve shirts, because the stuff is also absorbed through the skin. Wear goggles. The overspray tends to sting the eyes.

The 2k urethanes reduce with lacquer thinner. They are expensive per gallon but you save in terms of time and build.

I know a company that lays down a barrier coat of shellac first and topcoats over that. Do that at your own risk, even though I do not see the risk. But stepping outside the tech sheets is always at your own risk.

The shellac is a good bonding coat for metal and wood. Use Zinsser's Sealcoat because it is ready-to-spray and it is dewaxed.

From the original questioner:
We have been using epoxy to seal/pore fill. I assume there would be no problems there with the 2K urethanes? The epoxy works well.

From Bob Niemeyer, forum technical advisor:
It looks like everybody has an opinion on 2k PU. Let's look at it this way. CV is now banned in many areas of Europe due to the toxicity of formaldehyde that is released for the life of the coating. This is the nasty stuff that burns your eyes and nose. Doesn't the US government have limits on it for building materials?

The ISO limits in 2k urethane are so low that it is measured in the parts per million and it doesn't even get close to any OSHA limits. Also, ISO has not been proven to cause any type of cancer at all. It has been on the suspected list for over 40 years; if they have not proved it by now, they won't. We have found that all free ISO is mainly gone in the spray booth.

I have finished for several decades, and finished many pieces on location with CV and PU's. I will take PU any day of the week. Also, the customers say that all the smell is gone within the next day with PU, whereas the CV hangs on for weeks and weeks as it cures.

Follow data sheets for the PU you choose to use. Many do not reduce with lacquer thinner. Some do have build limits and many have much higher limits.

ICA wood coatings has won the European "Life" award with an Iso catalyzed waterbased PU. The "Life" award is for products that are sensitive to the environment and contribute to the reduction of pollution. Nobody else has won this award with a 2k waterbased PU.

From the original questioner:
Thanks for all the great info. I'm convinced that I would like to try this stuff out. I'm still trying to locate a supplier, though. I can't find any distributor info on the ICA stuff.

From contributor J:
Chemcraft makes (or at least distributes) 2k poly. Dealers are a little easier to come by for this. Where are you located?

From the original questioner:
Southern IN, near Evansville.

I finally located a SW nearby that carries the Polane 2K urethane. How does the SW stuff stack up against the ILVA/ICA stuff? The SW is $48 a gallon.

From contributor D:
2K is the nuts. I started finishing as an auto body man painting cars with polyester and acrylic urethane basecoat/clearcoat systems and then did wood finishing using the frankly stone age lacquer and conversion varnishes typically used.

2K kills that stuff in every conceivable way and polishes better than anything else available. I have always used an air supplied hood, simply because it's less of a pain than a respirator, so the ISOs don't bother me. On the general subject of ISOs, I agree with Bob.

From contributor G:
Try Rollie Williams Paint Spot in Elkhart.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor B:
If you're looking for a 2k urethane, Milesi has a full line of 2k urethanes, both solvent and waterborne. Also, Milesi has developed a 275 VOC 2k Polyurethane as well as a new, patent pending anti-.scratch line of 2ks. If you're located in the Indiana/Michigan/Ohio/Kentucky area, there is a distributor in South Bend, Indiana that covers much of that area, United Coatings Technologies, Inc.