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[email protected] nailshooter41@aol.com is offline
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Default Minwax fast drying polyurethane dries to white haze

On Thursday, October 22, 2015 at 5:48:22 PM UTC-5, Mike Marlow wrote:
woodchucker wrote:


A long time ago, I sprayed regularly (lacquer (automotive) , dope
(airplanes) imron (airplanes (both models and full size), buses, some
cars) ) . Both for myself and for other people. Up here in the North
East when it gets humid, I would have problems with hazing. So a
little retarder would allow it to slow the drying process, and not
fully trap the humidity into the finish.
Without knowing the chemistry of it, I assumed it was :
By slow drying it would get pushed out in the gassing off process of
drying.
The retarder idea came from the supply shop I used to get all my
paints from.


That explains a lot Jeff. Most of today's finishes are not lacquer - which
did indeed suffer those issues like you experienced back then. Not so much
today - not at all. I'm still thinking about the OP's post - if he used
poly then I really can't understand why he experienced what he did,


I am with you on this one, Mike. In context, using the reference point set out in the post as using off the shelf polyurethane I haven't seen hazing. That is my personal experience from many years, but certainly doesn't mean that will be everyone's experience. I shoot poly, high VOC alkyds, etc. with no concerning even when it is raining outside and I can shoot parts and pieces in a garage. During the winter it rains a lot down here in South Texas (our version of snow) and during the summer we have have about 3 months where temps hover around 100 during the day with humidity around 75%. Different challenges for any finisher. Add to the fact that we sometimes have 25 degree changes in a day, and you mixes change drastically from morning to afternoon.

So back to the question of fast dry Minwax. Even as a fast dry product, it is a 2 to four dry period when applied as a first coat, which means it fast dry for poly, NOT for a finish. The super high performance product I shoot on kitchen cabinets has a 20 minute dry/recoat. That's fast. Any mistakes in prep and your finish is fouled. Two to four hours of drying is a lot more forgiving, and should be plenty of time for outgassing. The only time I have ever had any blush was when I was "pushing" lacquer finishes on cabinets I was shooting in a warehouse while it was raining outside and I was coating every thirty minutes. Four coats later, and there was blushing (haze)in certain areas.

I would bet that the reason there was blushing on the Minwax finish (which I know many folks hate, but having shot/padded/brushed many gallons of it like)is incorrect surface prep. If you target isn't properly stored, the surfaces can hold a great deal of humidity, making the surface nearly wet. A perfect storm would be to have a lot of humid weather and have your project out in a shop or garage that isn't under humidity control, and go out and finish it on the first sunny day. The wood is full of moisture, and a warm day will cause the poly to cure from the top down, trapping the outgassing solvents.

As a tip to anyone that might still be reading this thread, if you are in a humid area and still need to do some poly finishing, get the slow dry products (hence the retarder Jeff referenced, although I know of none for over the counter poly for wood workers)that are the old fashioned oil based 6 to 8 hour dry. Before you apply your finish, wipe it down well with cheap lacquer thinner and it will dry out the surfaces very well and should eliminate blushing from simply moisture contamination.

Robert