Weird Finish Reaction

[Prashun Patel]

I have something weird happening on a test piece of eucalyptus:

The piece is BLO'd, then shellac'd, then coated with about 4 coats of Waterlox.

The day after applying the last coat of waterlox, I left the piece on my dashboard. At noon, the next day, The waterlox has bubbled and separated from the wood in random places.

It was sunny, and I'm guessing the dash was probably about 130-160 degrees F.

PLEASE tell me that the waterlox can do this if heated before properly cured. PLEASE don't tell me that waterlox is incompatible with WAXED shellac, which is what I used, and that heat just accellerated what's gonna happen to the rest of my piece.

Shawn.

What happened.

[Howard Acheson]

I have never worked with eucalyptus but if it is like many other tropical, fragrant woods, oil based finishes may not be compatible. The reaction you describe is the same one you will get with rosewoods and other similar woods.

Those types of woods require that they be coated with shellac or lacquer. You can apply the shellac as the first coat and it will act as barrier to the oils in the wood. Oil based finishes can then be used for subsequent coats.

At this point, you will have to strip off the existing finish and start over.

There is a chance that your problem was exacerbated by treating a new finish the way you did. Oil based finishes dry in two steps. First, the thinners evaporate and the surface becomes tack free. However, the varnish then begins to mix with oxygen to form a hard, durable and well adhered film. It takes 3-4 weeks for an oil based finish to become fully cured. Putting it in the sun and letting it get to that temperature will play havoc with any finish.

If you are going to use these types of woods, you need to research the types of finishes that work or, don't work.

Here is some other info about eucalyptus from Wikipedia:

On warm days vaporised eucalyptus oil rises above the bush to create the characteristic distant blue haze of the Australian landscape. Eucalyptus oil is highly flammable (trees have been known to explode[) and bush fires can travel easily through the oil-rich air of the tree crowns.

[Prashun Patel]

Thanks as always, Howard.
I did put a barrier coat of shellac on after the BLO - but just because I liked the color effect and am experimenting.

I have about 40 bdft finished like this. The rest is drying at 70degF. I haven't noticed the slightest bit of bubbling or oil seepage on any of the other wood.

I tried researching eucalyptus (grandis) as a lumber, but even the guy @ Willard Bros knew very little about it. The best he could tell me is that it has a similar grain pattern to Mahogany. However, I find that there's where the similarity ends. Mahogany is a TOTALLY different color, and has a completely different pore structure.

I'll report back if the rest of my pieces start to destruct too.

Shawn

[David Romano]

I am suspicious about the shellac step. Can't comment on it's compatibility with Waterlox in particular, but regular shellac is not generally recommended under most other finishes. This is what dewaxed shellac is for. You probably could have put the Waterlox directly over the BLO.

David

[Jim Becker]

David, waxy shellac is just fine under non-polyurethane varnishes...they will not have adhesion issues. Poly or a water borne product requires the de-waxed shellac. I'm suspecting that the heat has something to do with Shawn's problem and it may be related to what Howard brings up...the wood, itself, if oily, may not provide very good adhesion, despite the shellac step.

[Chris Padilla]

http://library.csustan.edu/bsantos/section2.htm Go to the middle of the page to Uses as Hardwood.

Interesting history on Eucalyptus, originally from Australia, of course.

[Prashun Patel]

That was an interesting read; thanks, Chris.

Eucalyptus has slowly 'grown' on me. The light pinkish hue doesn't really do much for me until topcoated. I find it to machine fairly well. It doesn't splinter as bad as I've heard Lyptus can, but it DOES chip out on cross cuts a little more than other woods. Taping the cuts / ZCI'ing them or the other standard techniques mitigated that for me - and I'm using like $50 mediocre blades on my miter and tablesaw.

The thing I DON'T like about it is what it does to the blade. It seems to pitch up the blade really badly. I mean, I ripped about 30 feet with a new blade before it started burning the cuts. I had to clean the blade twice during my last project. Same goes for sanding; it clogs paper faster than I'm accustomed to on birch and maple and oak.

There's a good amount of color variation in boards too. Some are white, some are pink; don't really notice the diff until sanded and topped. Sometimes there are black streaks deep in the grain that are not removable. Stain seems to absorb evenly but preferentially at the grain lines.

Overall, I'm not that impressed with it, but I'm comparing it to my Halle Berry piece of Mahogany

[Jeff Jewitt]

The culprit is indeed the shellac. Shellac holds in a fair amount (as high as 15%) of it's alcohol solvent for a while. What happened is that the heat caused some of the free alcohol in the shellac to turn to a gas, which caused the blistering. It's not the Waterlox's fault.
I'm not sure you need the shellac anyway. While you may experience some nuances in appearance with the 3 layers of finish, it's better to just use the Waterlox all the way. I'm pretty sure the Eucalyptus doesn't impede the cure of oil based finishes on it, but you may want to run a test to make sure. Wipe the wood with lacquer thinner first before applying the W/L.

We've seen the same thing with items in moving vans, guitar trunks, etc that are finished with shellac.

[Prashun Patel]

Yikes. So will the alcohol migrate out more gently over time as it cures if I keep the other pieces in cooler environments?