WWA Info Exchange

I apologize for the length of this post ahead of time but it will show you the measure of my frustration. I am in the midst of completing a coffee table and I'm having a serious problem with the finish on the table top. The frame is completed including the finish. I'm now doing the bottom shelf and the table top. I'm only having a problem with the table top. The wood is Lyptus. The finish regimen is as follows:

1. Sand to 220
2. Wipe with tack cloth
3. One coat of Minwax oil-based red mahogany stain. Let soak for 5 minutes and wipe off. Let dry.
4. Wipe on a coat of oil-based satin poly thinned 25% with mineral spirits
5. Sand with 220 when dry, wipe with tack cloth
6. Repeat poly coats and sanding until it levels out

This has been the regimen I've used for two previous projects and for this one. It has worked really well until the table top. Temperatures have been 60 - 80 and humidity has been 40 - 80 although I usually apply the finish when it's around 75 and 50% and let it dry for 24 hours. I keep the wood inside at night to keep humidity below 80%.

What appears to be happening is that the absorption of the poly into the wood is happening at various rates. When I brush on a coat of poly I end up with "islands" of poly on the surface that are very visible in oblique light. Yesterday I heavily sanded the surface with 220 to level it out and get rid of the islands. Today I wiped on a coat of poly in hopes that it would be thinner and would level out better. I didn't get islands but it still seems like the absorption is not uniform. I'm not sure whether I should just keep wiping on coats until it evens out or whether I've done something fundamentally wrong.

The bottom shelf is being finished at the same time and it looks fine so I think that rules out bad poly or bad stain. Here is a picture of what is happening. If you look at the area where the sun is reflecting you will see the alternating matte/shiny spots.



Any advice that anyone can give would be greatly appreciated - as always.

Hey PK, first of I love the look of the top and even the stain.

On to the problem at hand. I'm no expert by any means, but this looks a lot like problems I've have with oily wood and poly. I solved mine by sanding off the poly and going with shellac. You might give that a shot.

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Was the board in question exposed to any solvents/chemicals etc that you know of? Lots of things (including wiping down with a tack cloth that had a little/wax/silicone/polish on it or being on top of a stack when something funny is sprayed nearby) could cause problems with inconsistant coverage. You may need to let it completely cure, sand down to the wood, and try over. You also may try letting things COMPLETELY cure (2 weeks-1 month) and then give it a light sanding and try putting coats on top... but you may get witness marks from the spots the finish is not sticking...

I do as Frank suggested and use shellac as a base on just about everything I do.

Lawrence

P K : If shellac is used as a sealer coat in other finishing processes I think ICE PIRATE has a good idea. Would a sanding off of the poly really be necessary though? If you build coats of 3#-4# cut shellac scuff sanding for nibs between coats then lay on the poly high gloss coats first for more poly solids then a satin coat for sheen I think you would be home. I don't think the mottled sheen would be visible after the seal coat/poly finish is complete.

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newtooth 311
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It was exposed to everything that all the other boards were exposed to as far as I can remember. I used the same tack cloth on all the wood and this is the only board with the problem. That's what is so puzzling to me.

Hey PK,

I agree that a coat of blond dewaxed shellac, like SealCoat™ is your best bet. It's unfortunate that we didn't get to you before you put the poly on, but it shouldn't make too much difference.

It's important, particularly with your humidity, that you use fresh shellac, and that you let it dry thoroughly. The humidity will make that difficult, but it's important to maintaining the clarity of your overall finish, particularly if you are going to top coat it with poly.

Good luck,
Tom

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Thanks for all the help. Does this say I should not remove the poly? Just put a sealer coat of shellac on top and go from there?

I'm not sure and am waiting the others' answers with (almost) as much anticipation as you. One thing about it... shellac dries so danged fast that I don't think it would hurt anything to try it-- if it doesn't work you've only lost a little time. The biggest thing I can think that might screw things up for you is that the shellac will possibly alter the coloration of this board in comparason to the others... I would definately try things out on the bottom first and see how things look.

Lawrence

Thanks Lawrence. As dark as the red mahogany stain is, I'm not sure that the slight blond/orange color from the Sealcoat would be an issue. I have some Sealcoat (pretty fresh) so I may try it tomorrow and see if it evens out the sheen on the top. The problem is not that it is uneven in height but rather that it is uneven in sheen. If shellac would even it out then I would be home free. If it doesn't work then it's time to pull out the ROS and go from there - after a few days curing time. At that point, the boat may be out of the shop and I will be able to give it a longer curing time

PK... what? You don't call me? Sniff... sniff...

Yeah, you can sand that thing down with some 220 to get it nice and flat, then hit it with a coat of seal coat (I'd thin it down half and half with Denatured Alcohol), then, once that dries, sand that down with 400. Then, refinish with poly...

You are da man!

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I don't see rag or brush margins where the urethane has failed to adhere, so I would not go with the contamination theory, just the grain reversals accepting the finish differently. Sometimes you can do the same to yourself by not getting an even tooth on the surface. The next coat will adhere where sanded, draw back where not. Doesn't look like that's a player either.

I'd tooth with 320 or 400 then wipe with mineral spirits. Put on the number of coats required to even things out. Save shellac for the future.

You're not thinning a wipe-on are you? That would really cut back on the solids. You want them to build a finish.

PK, I talked to the professor at Palomar Cabinet & Furniture College and he says "bleedback" is not uncommon and can be dealt with without sanding back. When applying the finish, don't just wipe it down and leave it to dry. You need to go back about every half hour and wipe it down again. Each time you will see less bleedback and each coat will produce less bleedback.
I, personally, have experienced this kind of problem with oil finish and used this remedy successfully but I have not using poly.
good luck,
don