how many urethanes?

[Andy Cole]

could someone point me toward an article explaining urethanes (and/or a urethane varnish) i have been reading a lot of custom finish mixes and in some cases the term polyurethane is an ingredient and some others say urethane or urethane varnish. is there a difference, i know there are water based and oil based poly's but is urethane simply short for polyurethane or are the products different alltogether?

also, and this may be a dumb question but i never see laquer as an added ingredient in oil finishes, i have seen it as a top coat but can it be mixed with oils to produce a finish with protection or should it always be applied as a top coat only?

thanks for any help, finishing is a door to a fairly empty room for me as of now!

[Scott Holmes]

Hi Andy,

In short most polys are urethane resin varnish. There are different type of urethanes but generally are equivilent in the finishes available to the general public. Many polys have alkyd resin add to the mix to make the varnish a bit harder.

There are several company "maketing guys" now calling a water-borne acrylic finish "water-based poly". Not true.
There are many water-borne acrylic finishes that have a small amount of urethnane resin added to the mix to make it a bit tougher but most have 2%-5% urethane resin and are usually 25% or more acrylic. These are not VARNISH.

Nitrocellulose lacquer is a differnt animal altogether. It was invented ~ 1920 to replace shellac which was not available due to WWI.

Shellac and NClacquer are evaporative finishes meaning if you add the solvent to teh dried finish it will redissolve. This has advantages and disadvantages. NC lacquer doesn"t mix with other finishes nor play nice with some finishes.

[Andy Cole]

thanks scott, the reason for the question, mainly i guess, involves the sam maloof blend, in researching custom blends i ran across multiple articles (i'm assuming due to popularity of his chairs) describing the blend of oils one third tung, one third linseed, and (then the discrepancy) some said one third polyurethane and others say one third urethane, i had never seen a product that was urethane, always polyurethane and wanted to get the right mix for some test samples....thank you

[Howard Acheson]

Andy, for all intents and purposes, poly, polyurethane and urethane are all the same. In oil based finishes urethane is used either wholly (100%) or partially mixed with alkyd resin. Both will be marketed as poly, polyurethane or urethane. The only way to know what the percentage of urethane is, is to get copy of their MSDS. Even that may not give you a complete story.

The Maloof blend needs to be used carefully. It's not a very protective or durable finish. It ends up being mostly linseed and tung oil with portion of varnish. If making your own, non-poly varnish or poly varnish can be used. The Maloof finish properly applied makes a nice soft glowing finish that is particularly nice on cherry and looks pretty good on walnut. It requires fairly frequent application of oil and wax finishing material. It's also not particularly good as a finish if there are children around. It's quite soft and not particularly easy to fix.

You can buy the Maloof finishes from Rockler. No need to make your own.

[Prashun Patel]

Andy, if you want a handrubbed look, the key is the application - not so much the ratio of the materials.

Maloof's mix is indeed equal parts semigloss polyurethane, tung oil, and BLO. This has caused controversy, because a traditional oil/varnish blend involves some thinner (MS) and almost never two types of oil. The oil slows drying and the thinner increases mobility. These two things help make the varnish (poly or otherwise) easy to rub around and rub in.

Rubbing in is kind of a misperception. Most of the finish ends up on the cloth used to rub it. However, moving it around causes the thinnest of polishing coats to be put on, and also picks up almost all dust. These 2 things make the surface smooth.

You can achieve the a similar type of look with more protection by using a pure wiping varnish (50/50~) varnish and thinner. You have to move quicker, though because it will start to tack up sooner than with oil. Also, since any wood will absorb finish at different rates, some areas will seal completely within a coat or two - others may take multiple coats. The ones that seal quickest will then begin to build a film. Ultimately, it will all appear even - but if you want an in-the-wood finish with a wipe-on varnish you have to either a) wipe very aggressively and don't let the 2nd and subsequent coats sit on the wood for more than a few seconds; work in small areas or b) - and this is easier - sand with 220 or 400g between every coat; you can even wetsand the varnish; just wipe all slurry completely off after each coat.