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Archive for May, 2010

No, I’m not talking about the Gulf oil spill. I am talking about stain.

With the introduction of Waterbased finishes, and more so, with the improvement of them and the introduction of stiffer environmental laws, woodworkers have been switching from lacquers, etc to WBs.

I like Waterbased finishes — I’ve been using them for over twenty years. They’re not as deadly, they clean up easier, they’re easy to spray. Down side is that they don’t bring out the natural color of the wood as well as lacquer or shellac.

Waterbased stains, on the other hand,  pretty much suck. They don’t wipe on well, they dry too fast causing uneven coloration, and they raise the grain of the wood. So a lot of woodworkers use oil stains under their WB finishes. Oil based stains wipe on relatively easily, they spread well, and you can wipe the entire wood surface and get an even color. Oil based gel stains are even better because they don’t blotch hard to stain woods such as Cherry & Alder.

So here’s where I’m going with this: For my current project, The Computer Station from …, I’m using a Gel stain from Bartleys® called Pennsylvania Cherry. It gives a beautiful color to the Cherry I’m using, but being an oil based stain, I need to protect it from the waterbased finishes I will apply over it — create a barrier — kind of like what they need to do in the Gulf of Mexico.

I have done this before, on a bedroom set several years ago, with good results, but this time I had a few places where the top coats have chipped off from the surface below. So I thought I would do an adhesion test to see if I’m going to have total failure on this job.
(One might think I’m a day late and a dollar short with this adhesion test because I have finished the entire set of cabinets with the exception of the backs and the desk’s top. But, I guess, I want to know if I would be better off using my regular waterbased sealer or de-waxed shellac as a barrier coat.)

Adhesion-test Cross check pattern

Cross check pattern cut into WB sealer

An adhesion test is relatively simple: You apply the finish to a sample in the  manner that you will apply it to the final piece. After it dries, you take a razor & cut a pattern into & through the finish. Then apply a piece of tape to the cross hatch section and yank it off. Look for any lifting of the finish. If the tape is clean, you’re good to go.

This first picture shows my test after applying a WB stain, then the oil based gel stain, then a WB sealer.

Normally, I would put down a Shellac barrier coat after the gel stain, but I wanted to see if I could get away without the shellac. (Current wisdom says to use de-waxed shellac — Zinsser Seal Coat — over anything that might cause adhesion problems with later finish coats.)

Cross hatch pattern taped

Tape is applied over the cross hatch pattern

This picture I have the masking tape applied. Next I yank it off.

Cross hatch pattern after pulling off the tape

Cross hatch pattern after pulling off the tape

Pulling off the tape caused no finish to lift. I was pleased. So I sprayed all my cabinet backs using Waterbased sealer rather than Shellac and then a final top coat of the waterbased finish (General Finish’s Enduro® clear Poly, satin sheen.

Now, the last thing to spray is the infamous desk’s top. I have one more wood sample that I can use for testing. This sample I have divided in half; applying my spray stain, then oil gel stain, and then spraying shellac on 1/2 and WB sealer on the other 1/2. (I sand between all coats, plus let the gel stain dry for a couple of days before sanding and applying the sealers.) Finally, I sprayed the whole sample with my WB topcoat.

Results this time weren’t so good….

2nd adhesion test peel

tape shows ragged edges on cross hatch pattern

Looking through the tape shows more finish lifting on the left side than on the right side. Though, no finish lifted from the squares themselves. A scratch test using my fingernail lifted the waterbased sealer side’s finish easier than the Shellac sealer’s side too.

So, what does all this tell us, class?? Who knows! ;-)  No, it tells me three things:
1) Always use Shellac as a barrier between oil based stains and Waterbased topcoats.
2) I can spray non essential cabinet parts (like backs) using WB sealer because they’re not apt to get abuse and it’s easier than spraying shellac–simpler clean up.
3) NEVER USE OIL STAINS AGAIN!!!! It’s entirely too much of a pain in the ass.

What I really wanted to know, though, is will the finish on the desk’s top fail? I still don’t know. I did use Shellac over the oil base gel stain so chances of failure are lessened. But only time will tell for sure.

We’ll see how I fare with never using oil based stains again.  Class dismissed.

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