Lacquer Versus Polyurethane

      A question about lacquer and polyurethane drying times ends with a neat explanation of the differing ways in which waterborne and solventborne finishes dry and cure. July 14, 2010

Question
What are the recommended drying times between each stage of spray process for PU lacquer? Here is what I do.

1. Base coat #1.
2. Base coat #2.
3. Stain color coat with lacquer.
4. Clear top coat.

Forum Responses
(Finishing Forum)
From contributor B:
What's PU lacquer?



From contributor F:
It should tell you on the can or the product information sheets.


From the original questioner:
PU = Polyurethane. I'm a junior design professional and have started a new job where I liaise closely with the workshops. I'd just like to have an idea to best practice for drying times between coats of lacquer (just so i know that they are not pushing the schedule too fast).


From contributor F:
You need to check the product information sheets or the can, especially when you say polyurethane lacquer. To the best of my knowledge polyurethane lacquer does not exist. You can have polyurethane or you can have lacquer. Then into each of those categories are a myriad of different products with different drying times. In the amount of time it will take you to respond to my post, you could look up the information yourself and then know for sure. You need to specify the exact product you are using to get a reasonable answer here anyways.

You canít really push the schedule too fast. If you do, you will not be able to sand between coats as the paper will gum up, and the product will offer no print resistance. If you donít currently have any problems with sanding, or any problems with your drying racks marking the finish, you are probably not going too fast. That being said, some products do have re-coat windows. Spec sheets will tell you this. They are readily available on the internet or from a quick phone call to the manufacturer.



From the original questioner:
Thanks to all for the replies. I'm Europe based. Maybe PU is not available in North America. I'll take your advise check is out with lacquer manufacturer.


From contributor B:
If you are in Europe, check with ICA or ILVA or maybe AKZO for your needs.


From contributor D:
In Europe PU lacquer means plural component polyurethane just like what you can get from Ilva Polimeri, Melesi, ICA and Akzo Nobel. The word lacquer refers to the fact that it dries to the touch relatively fast because of its exposure to air. In America the word lacquer refers to the resin used whether it's acrylic, cellulose acetate butyrate (CAB) or plain old nitrocellulose. These resins are dissolved in strong solvents.

Waterbase companies like to call some of their finishes lacquer but this is sort of confusing because they don't behave at all like the solvent lacquers which existed for decades before these coalescing finishes were ever developed. What's not confusing is that a waterbase finish is a coalescing finish and it shares its curing properties with other coalescing waterbase finishes more than it shares any properties with a lacquer, precat, polyurethane or whatever the label of the product wants to drive you to believe. Those resins may be present in the mix but they don't dictate in how those finishes dry (we know that a lacquer is evaporative, a precat will crosslink, a single component varnish is reactive as is a single component polyurethane, and so on but waterbase finishes first must coalesce and they are the only finishes which do that as part of their curing).



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