What Is Sanding Sealer & How To Use

Being a somewhat newbie to fine woodwork finishing I’m looking for information. I know how to paint and some staining but I’m nowhere near proficient. I see people using sanding sealer to treat wood as a first step. What, exactly, is sanding sealer and how is it used? If I use it first can I still stain after sanding? Will it prevent paint or stain bleed? Any typical use or application methods is what I’m looking for. TIA.

@Heyward43 H: I use a lot of sanding sealer, as I use a lot of maple and, IMNSHO, you cannot get a good stain finish on maple with using a sanding sealer.

There are basically two kinds of sanding sealer: shellac-based and lacquer-based. I’ve used both and don’t find a great deal of difference between the final results whichever I use. Basically, and without getting more technical than my competence allows, they are thinned down shellac or nitrocellulose lacquer.

In the case of shellac-based, you either buy a de-waxed shellac and dilute it with alcohol, or you can buy a pre-thinned shellac sanding sealer. I use Zinsser’s Seal Coat:

https://www.shellac.net/SandSealZin.html

It’s a 2-pound cut, meaning they dissolved 2 pounds of shellac flakes in a gallon of alcohol. You can read on the link that I posted on how to use it and its benefits. It’s getting more difficult to find in my area, but there is still one supplier. If you go for it, make sure it is the Sealcoat and not the “ordinary” Zinsser shellac, which is not de-waxed. You don’t want the waxed version if you are going to apply any finish on top of it.

Sealcoat is available in rattle cans, too.

Then, there is lacquer-based sanding sealers. As the name implies, this is a nitrocellulose lacquer thinned with lacquer thinners. It serves the same purpose and achieves the same results as the shellac-based sealer. I tend to use it if my topcoat is going to be a lacquer- based stain or clear lacquer top coat.

I’ve never found the lacquer-based sealers at a retail store. I am lucky to have a local industrial supply source that will sell to me.

It’s likely a good point here to emphasize that both these products should only be used in a very well ventilated area. Plus, masks are a must. These products are not people friendly. That said, used properly, they are likely as safe as many of the other products we use.

OK, now that I’ve shown off my meagre knowledge of all this, I’ll try to answer your other questions:

Yes, if you use it, you can stain afterwards. That’s it purpose, really. It seals the wood so that the wood’s structure is more uniform and you get a better looking stain application. Since the sealers are so thin, they penetrate relatively deeply into the wood and “harden” it up a bit.

They will, within reason, prevent stain bleed. Always test first. (Obvious, I know.). For example, I’ve done some v-carved picture frames and to get crisp stain lines, I use contac paper mask, then after v-carving, I spray the carved out features with sealer. Then, I spray the stain. I get virtually no bleed into the background wood.

That’s about it. I’m sure that you will hear from other, more experienced users, too.

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Wow! Good info Grant. That will get me further down the road than I was before. I really needed to know this before I started trying to stain projects. Finishing products are expensive and I didn’t want the trial and error method to waste product and thus money. I didn’t think full strength shellac or lacquer would let me stain afterwords so glad to know sanding sealer will work. I will do some testing on the woods I primarily use to see how it goes. Thanks again.