Sealcoat under wipe-on poly on walnut?

[Bennett Ostroff]

Hi all. Long time reader, first post! I'll get right to it: When using walnut, is there any good reason to use Zinsser Sealcoat as the first coat if I plan to build a finish with wipe-on poly, Waterlox, or other oil-based varnish? I know it sands well and dries fast, but so does the first coat of poly honestly. I'm using kiln dried walnut, no odors, resins, etc that need to be sealed.

I'm also wondering if there would ultimately be a difference in appearance using Sealcoat + varnish vs just varnish. I've done a couple samples and the Sealcoat doesn't darken quite as much as the poly or Waterlox (some were too close to tell), but I'm guessing the color will catch up once the additional varnish coats are applied over the Sealcoat?

Finally, would Sealcoat help build an initial film in sapwood-y areas that quickly suck up the first few coats of finish?

I usually sand to 120 or 180 and then sand the first coat with 320. Thanks!

[glenn bradley]

There can be a lot of different responses to this. The Seal Coat can act as a barrier or a binder coat if compatibility issues exist but, that doesn't sound like the question. Seal Coat will quickly absorb into areas just like other finishes will but, having sealed those areas should let your other finish not do so as extensively.

I'll assume your wipe on poly is oil based and in that regard the Waterlox and wipe on will give similar results in appearance. Walnut lightens over time so if you want to avoid or lessen that, a tint added to a shellac finish prior to you topcoat can have a few benefits. The sealing of high absorption areas, an evening of coloration differences and a sustaining of that color over time.

I work with a lot of walnut and add a bit of colorant to my thinned first coat of finish to do get the previously mentioned effects. I don't see doing this with shellac as better or worse so I would say it is a personal choice. An initial treatment with shellac is certainly more easily altered or corrected if you are unsure of the result but, you are using test boards. As long as you faithfully prepare your test board surfaces like your actual piece the results should be consistent.

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[Prashun Patel]

I think sealing with Sealcoat is a great idea. Walnut has varying porosity and it can take a couple coats of varnish to start getting build. Because of this, I am tempted when applying varnish over raw walnut, to wipe and re-wipe to make the absorby areas drink as much as possible. This can lead to streaks as some areas start to build quicker.

Poly is generally lighter than Waterlox Original Sealer Finish. It's slightly lighter than the other full-strength Waterlox products.

I use one of the following regimens depending what's on hand:

Sand to 240. Sealcoat. Sand with 400, then 600, wipe-on varnish (osf or poly)

Sand to 600. wipe-on varnish (OSF or poly)

[Jim Becker]

There is certainly no harm in starting with SealCoat before moving on to your wipe-on oil based varnish. Whether it's right for your project is a different story. Personally, I like to get oil into walnut before I get to clear coating because it brings out the color I prefer. (I generally only use air dried walnut, too, for the same reason) And because I use water borne top coats, I use the SealCoat to, well...seal as a barrier coat between the oil and what comes next. The shellac also adds a bit of amber that further warms up the color of the walnut. That said, you might want to see if you personally prefer the look of the oil based varnish directly on the walnut in comparison to SealCoat and then varnish. Test it out and see what you like the best because ultimately, it's about the look.