PLEASE, I need help: Oil based poly, terrible finish, no idea why.

[Larry]

When I posted earlier than I sometimes thin it a lot, that meant that I have went as much as 50/50.  It will take a lot more coats to get a build but I can put a lot more coats down, since it dries so fast.  Also since I often wipe it on that goes pretty fast.

You never have mentioned brand but that can also make a big difference. 

[Old Greenhorn]

When I posted earlier than I sometimes thin it a lot, that meant that I have went as much as 50/50.  It will take a lot more coats to get a build but I can put a lot more coats down, since it dries so fast.  Also since I often wipe it on that goes pretty fast.

You never have mentioned brand but that can also make a big difference.

I'm using verthane. Up until this 'event' it's been good to me. 
 Yes, I just went out now that it is dry (but not cured hard) and was thinking I need to thin just a little more. I am going to let it get hard, do a sanding with 400, then hit it again. Thanks for pointing out the coats are thinner and I will need more. That didn't pop into my head.
 I just keep learning, but the lessons  can be painful at times.

[Old Greenhorn]

Well I didn't have to wait until this morning to know I had a winner. I could see it last night. As planned I did a light sanding with a 400 mesh disc, cleaned it 3 times and put on another coat at 1pm today. It was too cold at 8am when I was ready, only 62° in the shop. SO I went off on a tree job and did it when I got back and the temp was at 69°. I can't seem to avoid the tiny dust particles, and I mean tiny, that show up in the wet finish. That will take some serious work making a spray hood with filtered air and I don't have room for that yet. But the interesting thing is2 hours later when it was dried (not cured) those dust flecks are invisible in the semi-gloss finish.  I may or may not have time for another coat tonight, then again in the morning before I head to the mill, but at least I am finally making positive forward progress. I may have thi ssucker finished by the end of next week (if nothing else goes wrong ;D) 
 Again, thanks to everyone for the help and advice. I could never do this stuff successfully without my FF family.

[Old Greenhorn]

I wanted to follow up here just to document my ongoing issues and results with this type of problem. In the last two years I am refining what I know, so I thought chronicling it here might help either myself for future reference or somebody else down the road.

1) I learned that this issue seems to come back like clockwork every fall season. Looking back through various threads I find myself complaining about it every October/November for the last 3 years. It has something to do with the ambient conditions in the shop during this period. So, I have found that keeping the shop temps in the mid 60's through the night and the low to mid 70's during the day (and while applying the finish) seem to help a good deal.

2) After the initial coat has cured, hand sanding with 220 to take out any brush marks or imperfections is all that is needed. Don't go back and re-sand everything dead smooth with the ROS. As always, make sure the work is VERY clean before the next coat, blow with air and wipe with Mineral spirits, then dry and check. Do it again if necessary.

3) As Larry (and others) said in the forgoing discussion, thinning up to 50% can work really well and that is a major change for me. Before I had only thinned up to 20% with mixed results based on other conditions. Having a really thin mix spreads out flatter and faster, dries quicker, and blends better. I don't mind extra coats if they only take minutes to apply. I thin it a LOT for the final finish (covering or 'show') coat, this improves the smoothness.

4) FILTER the poly if it is anything but a brand new can! I have been continuously been trying to find the source of those little 'dots' I mentioned above and think I have finally found it. As the can sits after opening, some elements in the finish begin to dry or skin. These are tiny and when you re-open the can and stir, you break them up and don't see them, but they are there and will work into the finish applied. I started filtering anything not 'new' and would find a few of these 'dots' in the filter screen. They are soft and tiny, but they are there! Life improved quite a bit after that revelation.

5) Brushes: I am still investigating and working on this. I like to use 'throw-aways' but will pack the brush in a tight small plastic bag and squeeze out the air between coats since it may only be 4-6 hours before I use the brush again. Any stiffness it might pick up goes away after a few dunks in the fresh mixed poly. BUT while in the bag, more of those 'dots' are drying and forming up on the brush, so you have to be vigilant to not use a brush that has any of those and start with a new brush. Anything over 6-8 hours is probably too long. I also have switched from 2" brushes to 1". It takes a little longer, but I have more control, especially around edges. (1" brushes are also cheaper, but that didn't occur to me until I was finding success with it.)

6) Drips and runs: Not mentioned in this thread before, but always an issue. Thinned finish runs and drips over adjacent edges much easier than the thicker stuff. So I had been masking all edges for a while, which is a pain to remove for hand sanding and cleaning, then re-apply for the next coat.  Eventually I learned that careful brushing and quickly wiping any drips worked well for the sloppy stuff, then after I give it a few minutes while I pack the brush and close the can I go back and check with a hand light and wipe all edges with a clean dry shop paper towel. You may not see it, but it will show up on the towel. I do it again in 15 to 30 minutes after the finish begins to set, just to be sure. This has saved me a lot of re-finishing adjacent surfaces.

7) Inspection: After the full coat is on, I go over every square inch of the surface with a hand light looking for holidays, streaks, brush hairs, human hairs (probably mine, I hope) or any other imperfections and fix them while the bruh is still open. Of course I always have done this in the past but never really with the care I am using now, changing the light direction to get the right reflection to see any minor flaw and fixing it has saved me a lot of refinishing time. Likewise I do this again about 30 minutes after the coat begins to set up while there is still a chance of a fix.


 I know it is more than likely that all the woodworkers here know and use all the above points without thinking about it. But slow guys like me have to learn the hard way and even at that, we may forget and have to re-learn it over and over.... the hard way. So I wanted to put it in writing for future reference when the time comes for me to re-learn it. It might be useful to others also. I'm not a woodworker, just a hack trying to fake my way through. SO far I have been getting away with it. ;D :D

[Tom King]

I somehow missed this thread the first time around.

I never had any luck with the disposable brushes other than for fiberglass work.  They shed bristles too much for me.

I use these.  Between coats the brush if first cleaned with mineral spirits, followed by Acetone on the bristles only.  I never dip the brush anywhere close to the ferrule, so no acetone ever gets under the ferrule.  Thinner alone could never clean a brush to like new for me.  The Acetone dries really quickly too.

These do wonderful and quick coats of varnish.  I clean them as soon as the coat was put on.

Amazon.com: REDTREE 10051 Badger Fine Finish Natural Bristle Paint Brush - 3" : Tools & Home Improvement

Other decent brushes for less money are the white bristle Captains Brushes, but I forget the manufacturer name.  They don't hold anything like the amount of varnish that the Badger bristles do.

My latest favorite for exterior varnish is Totalboat Lust.  It looks identical to other, older marine varnishes, but dries between coats in one hour in reasonable temperatures.  I put six coats on a pair of entry doors in one day a couple of years ago.

https://www.totalboat.com/blogs/totalboat/comparing-totalboat-varnishes-with-boatworks-today