How Does Lacquer Sanding Sealer Differ From Lacquer

[Mike Shields]

Before I start finishing a project, I'm trying to get educated on a method I have never used before; washcoat before stain to prevent blotching. My bible for wood finishing is Bob Flexner's Understanding Wood Finishing, where he explains lacquer "sanding sealers" make sanding easier because they powder when sanded, because of the addition of zinc stearate.

Visiting a local finish supplier, I read the labels of a commonly available spray lacquer, and the recommended sanding sealer from the same company. The product contents where exactly the same, without the addition of anything that would lead me to believe that the lacquer sanding sealer is probably just thinned lacquer.

Is the addition of zinc stearate not required? Or is this just a way for companies to sell more products?

Thanks,

Mike

[John TenEyck]

Or is this just a way for companies to sell more products?

Mostly. If the finish you are using says you must use their sealer under it, well then you are sort of stuck. If it says "self sealing" then there is no need to use a sealer underneath. If you use sandpaper coated with zinc stearate you can sand most finishes w/o issue once they are truly dry.

I try to keep things as simple as possible so if I want to apply a washcoat prior to staining I use Sealcoat shellac cut with DNA. Same thing if I want to put a sealer over the stain layer. Dewaxed shellac sticks to pretty much everything and pretty much everything sticks to it.

John

[Doug Hepler]

Mike,

Maybe we have two ideas mixed together here. I think you understand what a washcoat is meant to do. It does not matter greatly how you fill the microscopic pores in the wood. You could use sanding sealer as a washcoat. Thin it about 1 part sanding sealer to 3 parts solvent. In this case the zinc stearate would not be necessary, in fact it would be detrimental. When I use diluted sanding sealer as a washcoat I use it because the solvent dries fast, and I actually decant the clear varnish/lacquer off, leaving the stearate in the can. So, I can't see a reason to buy sanding sealer for this project.

I would suggest that you simply use the lacquer that you intend to use as a finish, thinned as I said. When it has dried, apply your stain. The bigger question is the nature of the stain. Is it oil based or water based? Will it dry hard? will it run when the first finish coat hits it? If so, I agree with John. Seal an oil stain with dewaxed shellac before applying lacquer finish coats. If the stain is water based it probably will not run under lacquer but it might run under shellac, so don't seal it with shellac.

In my ideal schedule, I wipe the washcoat off, leaving it in the pores. Then I wipe the stain off, leaving a very thin coat.

In addition to the possibility that the stain might run, you should work out how much to dilute the washcoat. The less you dilute it, the less stain the wood will take, with less risk of blotching.

You must work out the details on scrap or you could be very disappointed..

Doug

[Jim Becker]

It's important to understand that solvent based lacquer is a slightly different animal when it comes to things like "sanding sealer". With these products if you want to seal and sand, you should always use the manufacturer's specifically recommended, matching lacquer sanding sealer/vinyl sealer to insure chemical compatibility. (You should also be setup to safely use these products...) These products may include additional solids and/or stearates to aid in the leveling by sanding prior to applying finish coats.

That said, my own practices mirror what John mentioned...de-waxed shellac is my go-to and applied as thin as possible for use as a barrier, etc.

[Wayne Lomman]

No, sanding sealer and lacquer are not the same. Sanding dealers are designed to build quickly and dry rapidly to enhance productivity. Added to this is their easier sandability and you have a case for using it where time is money. If time is on your side, don't bother with it but there are plenty of shops where it is essential for production. Finish lacquers are typically a little lower in solids and contain more waxes etc for durability and feel. I gave up sanding sealer when numbers out the door was no longer the priority.

As far as your ingredients list goes, manufacturers are only obliged to name stuff to a certain extent so that their intellectual property is protected. There are other substances besides zinc stearate for sandability. Read an SDS and see how little they tell you about the composition.

Sealing before staining is not something I ever do. I don't know if it's my techniques or I don't use problem timber. My advice is to always get at least a 95% of your colour on the timber before any polished is applied otherwise you lose clarity. Cheers

[Lee Schierer]

Your problem is going to be the solvent in the lacquer. It will soften most other finishes, including stain. The good news is that each new layer of lacquer softens the previous layer and bonds without visible layers. I just completed some Hickory furniture for our home office that was stained with Minwax stain. I used Deft Brush on lacquer and applied a heavy first coat. If If brushed it much at all, I could see the stain coming off. I had no problem with subsequent coats. After the first two coats, I sanded lightly to get rid of any nubs and applied a third coat. Hickory is pretty dense so I achieved a nice smooth surface, not French Polish, but for a desk and filing cabinet it is fine. One more thing. Most of the lacquer was applied in ambient temperatures of 20-30 degrees F.

[John TenEyck]

As far as your ingredients list goes, manufacturers are only obliged to name stuff to a certain extent so that their intellectual property is protected. There are other substances besides zinc stearate for sandability. Read an SDS and see how little they tell you about the composition.

This is an important point. Ever since MSDS's were replaced by SDS's, or whatever they are now called, manufacturers are only required to disclose those substances that are deemed harmful. You can't even find out what resin is in many products now, unless the manufacturer decides they want to tell you for Marketing reasons.

John