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dpb

On 01/01/2016 8:28 AM, wrote:
....

I never knew they made it as a water base. Actually, I dont know how it
can be called "polyurethane" if it's water based. I though that
polyurethane means it's in a class of it's own, but closer to an oil
base.

Need to read up...the 'polyurethane' is simply the liquified plastic
component which is included in the carrier for application. Initially,
all were oil-based, yes, but EPA (and CA) have fixed that by
introduction of such strict VOC limitations that couldn't be met other
than by eliminating the hydrocarbons (the oil carrier, iow).

Oil-based polyurethanes are elastic resins in liquid form, mainly
comprise of acids derived from vegetable oil, nitrogen-based chemical
amalgams, and isocyanates, suspended in mineral spirits. As noted
above, restrictions on emissions has led to water-based polyurethane
products, basically the suspension of polyurethane in water. Needless
to say, there's some significant alchemy going on inside the can with
surfactants and the like to create a miscible mixture, but that's the
basic product.

A polyurethane coating cures when some of its chemical elements form
powerful links with one another after reacting with atmospheric oxygen
(hence the "poly" as opposed to simply "urethane").

There's now a whole new class of "water-based oil-modified" which are
low VOC-compliant, water-cleanup but with the characteristic amber color
of oil-based as opposed to the clear water-based.

I recall first learning about polyurethane in the early 1970s, and was
told it was superior to the old varnish. I also heard it was similar to
an epoxy coating. I never really questioned any of that, I just tried it
and liked it. I have not used any of that sort of thing in years. THese
days, moldings come pre-finished, and I use that. I was never a big fan
of anything that involves using a paint brush. I did make some patio
tables though and used tung oil, which I like the look, it's durable
outdoors, and just gets wiped on.

"Superior" is pretty generic term; as with most any product they have
strengths and weaknesses and specific applications where they're the
cat's meow and others, 'not so much'.

The wiping varnishes (of which the tung oil products are one) are indeed
very easy to apply, but they're one of the least durable of all
finishes. They have the advantage they're easy to repair/restore by
another application.

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