My varnish is doing me wrong

[IraRat]

Can't figure this one out at all:

I've had one exterior side skin of birch all varnished for like a month. It's a nice deep amber which is what I like and what I wanted for the exterior. The brand of varnish only called for 3 coats, so it got 3.

But yesterday, I finish the 3rd coat on the OTHER skin, and it's a lot lighter.

Yes, the varnish came from different "cans," but it's the same lot. My hardware guy had to buy a case of 6, and I've been buying a can at a time to spread the expense.

Also, this second piece of birch was bought at a different time than the first. (Simply recall Ira screw-up #1, where I cut the skins incorrectly/cut two identical and not facing and had to run and buy two more sheets.) However, it's the same brand of birch, and I would bet the farm that it's the same "lot" too, as if this mattered anyway when it comes to wood.

Now I'm not going to SWEAR that I sanded this second piece between coats identically to how I did the first, but I CAN swear that I didn't do it THAT much differently. I just hand-sanded using fine grade, per instructions.

But they're not even close.

Should I take this second piece and HEAVILY sand down to the wood, and varnish, to make it darker? Or should I go with light sanding and more coats of varnish?

Tom, this might be the perfect excuse to go buy an orbital sander this weejend. Someone outbid me on that crab.

[Cutterpup]

Yeah! Ira you now have a trailer with a "light side" and a "dark side" all I can say is "may the force be with you" as you travel thru out the universe.

Besides unless your eyes are six feet apart you only see one side at a time.

Dan

[IraRat]

Dan, believe me--I thought the same thing.

But there's no way I'm going to a gathering with Woody here in Florida with sides that don't match!!! I'd never hear the end of it.

[Michael W]

From your description, it sounds like you have done everything right by using material from the same batch. The differences in color may just be caused by differences in the grain of the wood. Did you stain the surface? If so, did you use the same brush to apply the topcoat as the stain? It is easy to contaminate the varnish with residual stain in your brush, effectively adding a tint to your topcoat.

If you have some scraps of each side left, perhaps you can try to recreate the situation and experiment by adding some tint to the lighter side for force a color match. If that works, recoat the ligher side on your trailer with the tinted varnish.

Some varnishes and urethanes have additives that can separate when sitting on the shelf. It is always a good idea to stir (not shake) them before and periodically, during application. Shaking adds bubbles that will harden on the surface when applied. A gentle stirring will keep the material mixed without adding bubbles.

[Woody]

IraRat,
Forget the orbital sander. If you dont know what your doing with it, you can burn throught the very thin verneer and cause another cosmetic problem, far worse than off color. Varnish as it cures will get a little darker after drying. Over time it will lighten back up with exposure to the sun. It could be a grainular difference in the panel themselves and the way it took the varnish also.. I personally wouldn't worry about it unless the difference really bothers you. Did you seal the backsides of your skins like I told you. If you have a water leak between the skins and the sidewall, it prevents staining from the back side penatrating thruogh to the front under the varnish coats

[IraRat]

It's like not even close to the same color. And everything was the same, including the brushes. (I used foam.)

Is it possible that since the first piece has been sitting inside the house for more than a month that it darkened THAT much? And I just didn't notice this gradual darkening over time?

With plenty more to do before attaching them anyway, maybe I'll just let it sit for a few weeks and see what happens. Worse comes to worst, off to HD for another piece! I didn't seal the backsides of these yet; I did it for the interior skins, but figured I could wait to do this for the exterior right before they go up.

The ONLY other thing I can think of, and I can't believe this would make a difference, is that the 2nd and 3rd coats on the "bad" second piece were applied in sunlight (kind of), against directions. I tried to maneuver it into a shaded area this past Saturday and Sunday, but as you know, we FINALLY had some sun to actually get some work done, and I couldn't count on doing it at dusk, like the first piece.

[lmh222]

You could try setting the lighter piece out in the sun for a few hours (preferably around noon so that it gets the most UV exposure) and see if it looks any darker. That really shouldn't have any effect if you're using an "outdoor" polyerethane that has UV blockers but it might be worth a try.

I had to replace a few of the wood panels in my bathroom and I wanted them to match as closely as possible so I tried putting a few of the new unfinished pieces out in the sun for a few hours. I was amazed at how much they darkened. They matched the 10-year-old pieces in the bathroom perfectly in just a few hours.

Was the first piece of birch out in the sun before you put the polyerethane on it? The darkening will happen much faster if the wood is bare.

~Lindsey

[Woody]

There are four possible causes:

The grain is tighter on one panel than the other causing the marked diferrence in color due to penetration differences. even though they may look the same. I had to search for two matching panels and found them. Instead of just grabbing two random sheets

The heat of the sun on the panel, expanded the grain or the panel became drier than the other one, allowing the varnish penetrate the wood deeper, than the other panel

The sun had lightened the panel due to time between doing the different panels

You did not mix/stir the varnish prior to use on the first one or mixed it and it settled prior to the second panel being sealed

My gut feeling is the panels are not matching grain patterns ( not cut from same tree ) and the took the varnish differrently, causing the marked difference in color. Not that big of a deal unless it really bothers you, then replace it. When you build your second one, you will remember this problem and not do it again. Just remember it is not how fast, it is how well you do it. You will be fine

[doug hodder]

Hey Ira.........what lot you get the wood out of does make a difference. I ordered a bunch of Sapele Mohogany for a boat and had it shipped in. I had to do something completely different with my plans as the grain was totally different from piece to piece. Birch will not look identical unless it is made from veneer from the same log. They all grow at different rates and since most of that stuff is farmed now they really push the growing cycles of it. Anyway....at least that has been my experience. But then I'm still dopey from driving from Minden. When I paint a vehicle with details that are going to require more than a quart of paint, or in the case of a large truck ie. Kenworth, I mix all the paint together prior to shooting it, that way I know that both gallons are the same color. Sorry, I can't help you on the Varnish, I don't have any experience with it....by the way your name came up several times in Minden, all good things too!! Doug Hodder

[Cary Winch]

Ira,

I am going to completely agree with Doug and Woody here. We buy our birch a pallet load at a time. All from the same batch and we still sort through and mark matching colors so the interior sides are close in shade and pattern. There usually will be a bunch in a row from the same tree which makes it easy.

I apply ALOT of varnish on birch and have never seen color variances from can to can. Sometimes a can will spray different through the spray gun, but it looks the same. If it is a Spar varnish it needs to mixed though because there are particals that need to be suspended before applying. I shake it because I spray it and the bubbles go away when shot through a spray gun. If brushing, stir only.

Whatever you do don't try to sand through the varnish, it will make a mess that will make you very sad. If you need to darken the wood slightly and are using a oil based urethane you can apply another coat. This will darken it some. keep applying coats to the light side until happy.

Cary

[Woody]

The only time I have ever seen a difference in color with matched wood from the same can is

From not mixing it periodically and the particulate settles to bottom

moisture varying(high moisture content in wood)in material being varnish getting trapped under varnish usually with horrible results (frosted or cloudy appearance)

Can not properly sealed and in warm place. the voilatle componets evaporate making spar varnish darker amber color. Shortens work time also.

dirty application equipment ie. spray guns, dirty brushes or rollers, pans etc.

[mikeschn]

I've noticed a radical color shift when I don't match the wood properly. In any given pile of wood, pieces can vary quite a bit. You may have to get another piece or two to get a good match.

But look at it this way. You're only going to build it once. So you spend an extra $10 or $20 on plywood to make sure it looks nice and you have a match. You'll be glad you did for many years to come.

And the piece that you don't use for the wall, use it for drawer bottoms... Nothing goes to waste!!!

Mike...

[doug hodder]

Maybe someone can answer this question. Since I don't know Jack about varnish, can temperature during application and curing affect the outcome? Also is it possible that he has different thicknesses of application that is driving this color difference? I use a lot of lacquer, and automotive clear and epoxy, but have no experience with varnish. Something that I do is that I don't dye or stain material until I'm going to do all of it at the same time, same with epoxy coat. Clear coat isn't so critical, just keep anything that might be UV sensitive out of sunlight until ready to go. Veneered ply can fade very quickly when exposed to sunlight, cut some samples and leave them out in the sun with another piece of material partially over them to see what I mean.... Just my experience, yours might be different.... Doug Hodder

[Woody]

my experience with spar varnish is once it is open, it ages, it gets alittle darker as the the violatile components start evaporating and it is exposed to air. The color change is not that dramatic of a shift just a little deeper amber color. You can run into problems with not mixing it once in awhile and get sheen differences, those are slight. Tempeture and relative humidity does affect curing times not color

I think IraRat's problem is mismatched wood, not from the same tree, it is as simple as that.

[madjack]

...I would have to agree with the differing wood theory. I have built a lot of furniture over the years and any differences in color has come from the wood...as long as the varnish is not contaminated and is well mixed. Ira, you can try additional coats or take a small amt of your varnish and a VERY little bit of stain and mix, then experiment on a piece of scrap to see if you can obtain a match. I generally try to spray my finishes and whether spraying or not I add a little laqueer thinner to it...makes it spread easier and setup/cure a little quicker along with making the particulate in the bottom of can breakdown and mix up better. FYI for anyone applying varnishes and urethanes...if it is cloudy day with extreme humidity...forget it and wait till the next day or you can end up with a finish that will hardly ever set up satisfactorily...I mean it can take a day (or 2 or 3) whereas on a better day it may setup in hours
madjack