Success with Finicky Polyurethanes

Some polyurethanes require just the right touch, and even an experienced finisher may experience runs, orange peel, or other problems. May 16, 2014

Question (WOODWEB Member) :
First of all, I am the production manager at my company and do not know a lot about finish. With that being said we have always used ML Campbell products, mostly CV, and for the most part we are pleased with it. We are a custom cabinet shop and do mostly painted and glazed or stain w/satin or dull topcoat. Lately we are getting more white inset jobs that are less forgiving that putting a glaze over the paint.

Also we have had some request for more high gloss finish, which brings me to my question. I am looking at a polyurethane product from Milesi. Is this a good product? Does it yellow over time? Is it easy for my finish guys to fine tune (problem solve, air bubbles, orange peel, etc.)? Salesman have been by here with the product, sprayed some samples and we like the product. At this point I am thinking about getting some and doing a few small projects to test it out. I am just trying to do some homework before we make any decisions. Thanks for any information you may have to share.

Forum Responses
(Finishing Forum)
From contributor H:
Milesi is first class stuff and itís pretty forgiving. Your concern should be the local distributor if he is keeping enough stock so you don't run out. The product comes into the states from Italy. I spray some of their waterbourne.

From contributor C:
I use 2K urethane from ILVA, another Italian company but the same concept. There are a couple of issues to watch out for. They have a shorter pot life and once catalyst is added there are between three-four hours to use product before it starts to harden. Also safety - your sprayers should be wearing supplied air respirators. My supplier no longer makes conversion varnish switching over completely to 2K urethanes.

From contributor W:
It better be super clean and you need to be willing to allow drying times that are different than conversion varnish. I'm in the middle of a bookcase unit right now using Milesi and we have had some issues with sags. It seems to either orange peel or run Ė there is very little wiggle room between the two.

From contributor X:
I know what you are saying about being trickier to spray than CV. There is a fine line between too much and not enough on vertical surfaces. I have learned to resist the temptation to put a little extra on vertical surfaces - definitely not as forgiving as CV.

From Contributor R:
Our shop tried that coating and found it to be a good product with the same drawbacks that you and Contributor X brought up. At the time, our shop had finishers with between 15 and 30 years under our belts. With some of the issues we were running into we used to comment to each other that "I've seen stray cats spray better than you". We needed a product that we could manipulate quicker than the Melesi and decided to stick with a CV.

From contributor A:
To contributor W: When you say you liked the Milesi sealer so much better - can you be a little more specific what you liked about it vs. the others?

From contributor W:
It just dries so fast for its solids. When rushed we were sanding it in an hour with quick 320, a little Scotch-Brite and topcoat. I wasn't crazy about that but production called and it had to go out to the friendís shop. I don't impress easily anymore and it did. I have sprayed the Chemcraft pu but it was no better than the ilva or the ica. Now that S-W bought out Sayerlack I would like to try it but they weren't ready for prime time when I did testing. They also quoted up some high pricing when shown.

When I said I would get orange peel or sags I was saying on the same 8" piece when sprayed vertically. I tried thinning at the min and at the max and still can't find the sweet spot. The job is com, even though the owner finds it had to let it stand four days before I start wet sanding and polishing it. I tried at three and two but it kept moving around and scratched instead of cutting. At four days it is magic. I use 1200, 1500, compound, and polish. Itís a lot of work but is very wet looking.

From contributor O:
I prefer 2k urethane over CV. Our shop does a lot of huge multi-floor commercial jobs. Having CV shatter is not an option (and it can happen even without it being your fault). I love the Milesi sealer as mentioned above but since Chemcraft was bought out by Akzo Nobel it is just too hard to get. We use Ilva products right now.

Spraying urethane is different than CV. I find on vertical surfaces you need a light tack coat, let it flash and then you can lay on 3.5 to 4 wet mils no problem. I find that some of the solvents they recommend don't layout as nice as I like. I prefer the TZ33 solvent or straight Butyl Acetate for the Ilva products and for gloss work I add a little MAK for a perfect off the gun gloss. We have a drying oven so I can successfully buff the next day if I have to but prefer a week for everything to shrink down before wet sanding.

As far as cost at 40% solids I can thin the urethane down 100% for open pore finishes or keep it at 30% for closed pore jobs and don't have to worry about my dry film thickness. Humidity is the biggest problem spraying urethane in our shop.