Shellac over Tung Oil

[Patrick Fischer]

I'm refinishing a parlor table. Dark stained ash was sanded lightly and restained. Topcoated with a stain/tung mix and then wetsanded with 600 grit using same mix. Nice and smooth, good color. Now for the final finish, I used shellac (premixed clear out of the can) and it almost immediately started to crinkle and looks like an orange peel..a really wrinkly orange peel. What did I do wrong? Think I can sand lightly and recoat with shellac? Do I have a serious incompatability of finishes here? Help.

Thanks, Patrick Fischer Olalla, WA

[alexy]

Bad shellac? Check date on can. And paint a little on a piece of glass. If it crinkles or stays gummy, you need to get fresh shellac. Clean off the old with alcohol and lots of rags. (I'd worry that light sanding may leave too much of the old bad finish on.

Oil not dry? Pure tung oil is very slow drying (actually, curing). Much slower than BLO, in my experience. E.g, a cloth used to wipe off BLO will usually be stiff within a few days, while for tung, it takes a few WEEKS. (My approach to avoiding spontaneous combustion is to lay out rags INDIVIDUALLY, allowing the oxidation but denying the heat build-up needed for spontaneous combustion.)

[Andy]

Might your shellac have too much wax (if it's not too old)? I know wax content affects how well it sticks to other finishes. If you didn't buy it dewaxed, you can let it sit for a few weeks and then pour off the top (clear) layer. (If you happen to have access to a centrifuge and some 50mL tubes in a biology lab, you can dewax your shellac much more quickly - it works like a charm).

[Hax Planx]

You can't apply shellac over wet oil. What you got was predictable. You can use shellac over oil (tung or boiled linseed), but you must use the bare minimum of oil to coat the wood and immediately and aggressively wipe away the excess. If you soak the wood, your shellac won't stick. You definitely soaked the wood, so yes you have a basic incompatibility. I think you need to strip the shellac. Sanding it all off will be a royal pain. Then you need to reconsider your top coat or not use one.

[Andy]

You can use denatured alcohol to strip the shellac, and AFAIK, that won't affect the oil underneath. Sounds easier than sanding.

[Tim Douglass]

I think that all you did was apply the shellac before the oil was thoroughly dry. I've been using shellac over Danish oil (which has dryers) and I generally allow 1-2 weeks before applying the shellac. I think that a pure tung oil or a mix with an oil stain like you used would require even more time.

I've never tried it, but I've heard that if you shine a heat lamp on your piece and any oil appears as it warms it still needs to dry longer. I'm into letting things dry longer than really necessary just to be on the safe side.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[Graham Walters]

Please excuse the dumb questions, but I thought each was a finish in its own right.

Why coat with Danish Oil first, why not just use shellac? Why put shellac over Danish Oil?

Thanks

Graham

[Hax Planx]

You can try, but it will take forever.

[Patriarch]

"Graham Walters" wrote in news:dahl3h$689$1$ [e-mail]:

The oil 'wets' the wood, and gives a different character to the finish, with the shellac over coats, than does the shellac alone.

'Danish' oil has some, usually quite small, varnish/resin properties, beyond that of a 'pure' oil. Note that all of these terms are relative, not absolute.

But previous posters are correct in that the oil(s) need to cure, before the shellac is applied. This goes beyond 'drying', or solvent evaporation, and deals with the oxidation & crosslinking of the molecules. Chris Minick authored an excellent article in FWW from about 3 months ago on the subject.

Don't give up on shellac. Don't hurry it, though. Woodfinishing takes patience, if done correctly. Screwing up, not so much.

Patriarch

[Tim Douglass]

The oil, any oil, tends to bring out the grain. I like the Danish oil because it drys better. The shellac provides a surface film that (if I ever manage to get good at it) can be polished to a mirror-like shine. Shellac by itself doesn't "pop" the grain the way the oil does. Oil finishes don't have the glossy look of shellac.

It's just a way of getting the look I want.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[Hax Planx]

bring something to kill"

completely wiping away the excess. You don't even have to wait to apply the shellac. See Jeff Jewitt article:

[Tim Douglass]

oil on the "flood it on until no more soaks in" basis. It's given me good results (better than my padding/French polishing technique gives) so far, but as I keep looking to better woods I want to explore different techniques.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[George]

French polishing really only requires the oil as lubricant. Since oil and water, or it's polar counterpart alcohol mix so poorly, the oil comes up through the film and is normally removed. For that reason, non-curing oils like mineral, olive, or grape are better choices for padding.

[nospambob]

[Tim Douglass]

The oil I'm talking about isn't for the French polishing, it is to pop the grain before I begin the polishing process. Maple seems to need something more than just the shellac to give it character and the oil first seems to fill the bill. I flood it and sand it in with 600 grit wet or dry. Let sit for 30 minutes and wipe off the excess. Generally I repeat the process the next day then let it dry for anywhere from a week to a month before starting the shellac process. So far, aside from the fact I can't seem to polish on a smooth enough finish, I've been getting essentially the look I want.

Mineral oil is my choice for the padding.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[Tim Douglass]

And some of us really need to be able to find the shop time to apply a finish more often than about twice a year. It seems like I forget everything I knew from time to time.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[George]

I like thinner oils, but you have compared a French polish with and without extra oil? Mostly what oil does is cut down on light scatter. Which the clear finish will do as well. Try it, you'll like it. Maybe even better'n oil plus. Keeps the maple whiter, too.

I don't believe in slurry sands, either, so I guess you'd have to do without that, too.

[Tim Douglass]

The oil significantly darkens the end grain portions of the figure, making them stand out a lot more than shellac alone. I am trying to get a slightly amber color anyway, so the oil is good for that too. I find the shellac alone on the maple is rather characterless to my eye. Next time I do a project with some figured maple I think I'll do some experiments - one of which will be going to a darker (not dark, just not super blonde) shellac. Unfortunately I'm not likely to get to another "real" woodworking project for at least 6 months or so, since I have a bunch of built-in cabinets to make from ply and MDF first. Just FWIW, MDF looks pretty cool french polished.

Maple doesn't really *need* the slurry sand, so it is just a matter of habit I guess.

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass

[Patriarch]

Tim Douglass wrote in news: [e-mail]:

THAT's an image that will take a while to get out of my head.

Patriarch

[Tim Douglass]

Heh, heh. I make my zero clearance inserts out of MDF. A couple months ago I was working on how to French polish (with limited success) and decided to wipe some shellac onto one of my inserts just to seal it and make it a bit smoother. After a couple of coats and a touch of wet sanding I decided to see how it would all polish out, so I wasted a bit of time getting a pretty nice polish on it. The important thing is that it gave me an insert that is slicker than glass and definitely doesn't look like it came out of a store!

-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"

Tim Douglass