Thinning with mineral spirits in cool weather

[Alex Horvath]

Hi all,

I recently applyed a varnish (McClosky heirloom varnish) to a table. I applied several unthinned coats without incident. The last coat I thinned about 10-15% with MS to get a perfectly flat surface (I think Jeff Jewitt calls this flow coating) but after 8 hours the finish was still wet and the next morning there was an oil film over most of the surface.

I have seen this lately even with painted finishes. With alkyd paint this effect totally kills the sheen. I think it's because temps are cool even though I'm applying the finsh at 70 degs. However overnight temps may go down to 50. I have done some painted objects outside in full sun and did not see this effect.

I suspect that the evaporation rate for mineral spirits is highly sensitive to temp and perhaps this really slows down the cure process?
Should I try adding some Japan Drier or just keep temps up for 8 hours+?

Thanks

[john lampros]

This 'oil film" was over the dried varnish? if that's the case you got some bad or contaminated MS which is common. I would switch to naptha for thinning as it contains no oil and is slightly hotter than MS meaning it will evaporate faster. It is made for those finishes and is often refered to as " paint and varnish makers naptha" or spirits. I'm assuming you stirred it thoroughly as they tend to settle and all the all the good stuff is in the bottom of the can. I would let dry for a few days before doing anything else tho. try to bring it inside where its warmer if your working in a garage. Or spot a halogen work light on it from a safe distance, about 3 feet. that should raise the surface temp at least 15 degrees. But dont turn it on till your done varnishing or the varnish will set to quickly on you and yank the hairs right outa your brush and your table will look like something you shot on safari. Best applied with an ox hair blend brush like a Capitol Ox by Elder Jenks. wont leave a brush mark. Be careful of oily rags or rags with oil paint on them as they have a tendency to catch fire even without an ignition source. lay them flat on the floor and they wont catch. or dunk them in a pot of water and hang to dry for reuse. I've seen this happen too many times. if you want anymore info on these subjects just holler.I cut myself short as i have a tendency to ramble john.

[Alex Horvath]

Thanks John,

yes, the film is over the finish and I can wipe it off but it does negatively affect the quality of the finish. I have had serious problems as of late with alkyd paint in cooler temps also.

I'm using the standard mineral spirits they sell at the box store. When I first started spraying alkyd paints, some pros suggested a better quality MS but I could never find it and I got good results at the time. Now I can only get good results if my work is in full sun or at least in warm temps outside. I know that some alkyd paint pros that spray alkyd paint use naptha.

Any idea where i can get the special naptha? I'll try my local Ben Moore store as they do have many pro products.
Of course I have the generic naptha and I can try that.

Thanks, this issue has been causing me difficulty for some time now with the paint (and no one has advice) and now I see it with the clear so I thought might get good a answer here.

I have the Dunnet Fitch brush. I could spray but to be honest I get tired of noisy shop equipment sometimes, especially for very small jobs.

And don't apologize for rambling - I have been an amatuer finisher for quite a while but it still amazes me what little detail can still trip me up. I thought by now I have had every possible mishap occur. I suppose there is no end to those for some of us:(

[john lampros]

Alex, painting and finishing is mostly chemistry and mishaps will always be there. Especially when dealing the unknown history of previous finishes and treatments which is just about always. Experience will teach you how to avoid most of them. you dont need "special naptha' big box naptha is naptha, one and the same, it just USE to be called paint and varnish makers naptha. A dunnet is a good brush but a little firm for varnishing so you'll need a very light touch. good for shelack and staining as I recall it use to be a badger skunk blend but I think they changed to a fake badger and dyed the dark stripe on, But rather short bristle length which makes for a fast brush, ideal for those paints mentioned as geting the product on quickly with good control is critical. The 60- 40 % ox china bristle is the best blend for varnish and enamel. soft but firm. soft enough to leave no brush marks and firm enough to have some speed. speed because you have a very limited time to get the product down and layed off while you still have some flow out left. too soft like a pure ox and you'll have little control and no speed and the finish will get away from you ( sets up faster than you can get it down and layed off and you end up with a ropey finish. (lots of brushmarks).best left to a pro.the 50- 50 or 60- 40 ox blend is a dream if you can find them. http://www.merrittsupply.com/Elder-Jenks-Capital-Ox-Fine-Finishing-Brushes-P7853.aspx
a (http://www.merrittsupply.com/Elder-Jenks-Capital-Ox-Fine-Finishing-Brushes-P7853.aspx) 2.5 " is about $30. a 2" is a sash tool for window sash and other fine detail a 3" is for doors and other large work. the 2.5 is the all around utility if you can only get 1 brush. Used every day they will only last about a month tops as the bristles wear down and become shorter and more scratchy. then they become stain and shelack brushes and after that they're only good for stirring paint. I digress, at least your table dried. the more i think about it the more i think it wasnt the cold temp. that kind of separation usually only occurs when below freezing. and usualy results in a very slow dry if any at all. so I'm thinking it was bad MS or bad finish ( was it a fresh can?) you cant go wrong with speeding up the drying process with a little hot light. the faster it dries the smoother the finish with horizontal surfaces as the less airborn crap gets stuck in your finish. avoid fans and any thing that moves air around stirring up all that dust.
well. I guess my fingers got away from me here and I'm starting to do the pee dance.

[Alex Horvath]

Thanks John,

Can't believe that brush is $9.

You are right that the finish is very old, probably a few years at least. I didn't mention this because the unthinned coats seemed to cure just fine. Also I was a little sloppy because as the finish in the small can was used up (I applied about 5 coats) it began to immediately form a thick skin in the can even when closed and at that point it might not be a good idea to continue using it.

I got some new finish and the results seem to be better.