How does the weather affect a finish?

[zeboim]

I'm soon to be putting an oil based finish on a project in my garage.  I live in southern Louisiana so as you can imagine the humidity is pretty high at all times.  We are also currently reaching temperatures at and above 100 degrees.  I would think that the high humidity would cause the finish to cure slower, but the heat would cause it to cure faster and cancel each other out.  I'm by no means an expert on finishes nor weather, so I'm expecting to be way off. 

This will be my first finish job, so any advice would be helpful and appreciated.

[Eric.]

In my experience humidity has more effect on cure times than temperature...i.e. high humidity and high temps slow down cure time more than low humidity and low temps...freezing temperatures not withstanding.  Err on the side of safety and give it plenty of time between coats.  And apply thin coats.  Oil takes forever to dry, especially coats subsequent to the first.

[AceHoleInOne]

In high humidity, it will slow the dry time. So air movement is key and will speed up the dry. Although, heat is a factor, it wont cancel out the humidity effect, sorry.  Make sure the finish is fresh. If not, do a test board to see how things dry. Try to coat your project early in the morning because it sucks dripping sweat all over a fresh finish.

 

-Ace-

[Tom Cancelleri]

Like the above posts. I have my shop climate controlled, however it is a 2 car garage and while I've done my best to seal it as best as possible, it's not perfect. When it's humid and hot outside my shop is 68 degrees with 62-65% relative humidity and my finishes are slow to cure, and I find I'm adding 12-18 additional hours between coats for oils. I put a coat of danish oil on my Roubo last week and yesterday was the first time I was able to use my bench since applying the oil, just because of the humidity. 

[wtnhighlander]

I had a bad experience with straight BLO last fall. I applied a heavy coat to my project, then wiped it back, before I left for work one morning. The temperature dropped several degrees during the day. Although I later wiped the surface down thoroughly, even with a little mineral spirits to remove the oil, it continued to weep out of the wood pores for nearly a month. This was a fresh can of oil from the nearest big-box store. I never bothered to look for a packaging date.

[AceHoleInOne]

Hey highlander, not sure oil finishes have dates on the can. Typically, shellacs and or pre-catalyzed solvents have a "use by" date. Some oil's cure by oxygen. So by fresh, I would recommend an unopened can. 

 

A lot has to do with the wood. If the wood is very porous and you flood the surface, The wood will pull the oil way down. A month seems a little long to still push out oil. But there is always a first time for everything and cold helps with that too. BLO, on its own, does take a long time to dry.  

 

-Ace-

[wtnhighlander]

Hey highlander, not sure oil finishes have dates on the can. Typically, shellacs and or pre-catalyzed solvents have a "use by" date. Some oil's cure by oxygen. So by fresh, I would recommend an unopened can. 

 

A lot has to do with the wood. If the wood is very porous and you flood the surface, The wood will pull the oil way down. A month seems a little long to still push out oil. But there is always a first time for everything and cold helps with that too. BLO, on its own, does take a long time to dry.  

 

-Ace-

If by 'porous' you mean Red Oak, then you hit the nail on the head! After about a week, the top surface of the table was dry to the touch, but bringing it into the warmer house seemed to make things worse. Every couple of days, I would have to wipe away the little stalactites of congealed oil that formed under the top.

[wdwerker]

Sounds about right to me too. If you use BLO very thin coats and be prepared to wait, sometimes for weeks.

I have a 20 year old can of Waterlox tung oil. It still is useful but there is a skin in the can I have to pop to pour any out. It dries a little faster than BLO but it still takes a week or so and I learned the hard way to use very thin coats. Even on maple I had oozing and a gelatinous goo in the inside corners that I had to scrape out after a month, then start over.

[RPCV_Woodworker]

If by 'porous' you mean Red Oak, then you hit the nail on the head! After about a week, the top surface of the table was dry to the touch, but bringing it into the warmer house seemed to make things worse. Every couple of days, I would have to wipe away the little stalactites of congealed oil that formed under the top.

I was about to ask if you were using Red Oak. I did a bunch of trim and windowsills with it, as well as a couple of tables, and that is pretty much par for the course.  Stains, oils, water, everything...

[PeteJr]

A few years ago I built a toy chest for my daughter in central Florida while we were visiting.  It was August and heat/humidity were 95+.  I pre-built the component pieces in my shop in NY then shipped everything ahead of our trip.  The assembly went well and with a few tools borrowed from a neighbor I completed the chest. 

Applying the oil based ebony color stain went well however my choice of brush on satin polyurethane was a near disaster.  The humidity caused the poly to cloud almost to a milky white.  On the ebony stain it looked terrible.

I finally obtained a very good finish by fine sanding the brushed on "cloudy" poly and applying the final 2 coats with the same poly but from a spray can.  I had to work very early in the morning at the coolest time of day and waited 24 hours between the final 2 coats.  The overspray tended to cloud up so I held the spray can 12" from the surface and made sure the spray coat was on the heavy side.