# Another Finishing Question



## RobH (Apr 25, 2007)

Hey all,

It seems that I got a good thread going with my topcoat question. I will just say that I would spray the shelves if I had the capability to spray.

Now, for tonight's question…

My dad asked me tonight why I did not use sanding sealer over the stain. I could not answer the question because I am not sure of the difference between sanding sealer, polyurethane, and lacquer. Could someone please help me out here?

Also, why not use sanding sealer instead of one of the other finished?

Thanks for the help,
Rob Hix


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## Karson (May 9, 2006)

I've seen two kinds of sanding sealer. Shellac based and lacquer based. The intent of sanding sealer is to make the wood fibers collect the sealer and when you lightly sand it you sand off the hardened wood fibers.

When you sand raw wood these wood fibers might be pressed down into the surface of the wood and are not sanded off. So the sealer makes them hard and you can then sand them off.

I said lightly sand because if you are too aggressive then you are back to the original wood surface again. And, back to the original problem.

Water makes the grain raise, so if you use a water based stain what you have done is raised the fibers of the grain and it feels rough again. So if you stain and then use a sanding sealer, you will be lightly sanding off the raised wood fibers that are stained and hardened.

The Zinsser shellac sanding sealer is a de-waxed sanding sealer. What de-waxed mean is that all of the wax has been removed. So the Zinsser sanding sealer can go over any previous finish and any new finish can go over it. Shellac is a natural prodect made from the Lac Bug and it is a secretion that they ooze out of their pores and completely cover their bodies. They are then stuck to the branches that they live and die on. They are harvested and heated and remove all bug and branch pices and make the shellac sheets. The workers pull it like you might pull taffy. It is then disolved in alcahol and you end up with shellac. When you purchase a dry version of shellac flakes you can get different shades, but in a pre mixed version only two. clear (yellow), and an orage version. The organge is great on Walnut, and Cherry.

If you have a waxed surface and try to cover it with a water-based polyurethane finish it won't stick. But if you cover it with Zinsser Sanding sealer and then use the water based poly it will stick.

I have seen but never used Lacquer sanding sealer.

I do use the Zinsser product all the time. I use it as the final finish also. It is the main ingredient of my French Polish finish. So I spray many coats of shellac and then wet sand with mineral oil and 400 - 600 grit sandpaper and then French Polish on top of that.

Shellac is not an outdoor finish. So some other exterior finish would be required.

You didn't say what your project was!


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## Radish (Apr 11, 2007)

I'm with Karson on the absolute utility of this wonderful product. It's the bomb.

As to the spraying, you can get in for less than the price of a good router (HVLP conversion gun and a small compressor). Since I do mainly small boxes, I use a small pancake compressor used to drive a brad gun (Porter Cable). If you don't run it full time it will handle bigger projects. I sprayed thinned outdoor enamel paint and refinished the wife's iron patio furniture with mine (good justification if you need wifely support on the purchase).

There are many ways to get a good finish. Spraying is a great way to get a good finish fast. And the widening availability of waterborne products makes it safe and you don't need a booth and an explosion proof fan etc. to spray in the garage workshop. Although the bookcase may not be the project for this as it is already in the works, I urge you to do some reading and mull over the possibilities that become available with a HVLP conversion or turbine gun. Jeff Jewitt and Andy Charron have some good books on the subject.


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## bbrooks (Jan 3, 2007)

Great information Karson and Doug. I have not used a sanding sealer before. Somewhere I read that you can just allow the first coat of your finish to be your sealer. Just apply it, lightly sand if needed, and then go from there. So far it works for me, but I have not been doing any french polishing like you Karson.


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## furnitologist (May 31, 2007)

RobH:

To add to K - D & B…....sanding sealer is one of those wood working topics that creates very strong opinions. Lacquer based Sanding sealer doesn't create the best bond….blah-blah-blah. The topic always creates too much information.

If you are in a production environment (100's of units) lacquer based sanding sealer is the way to go with a lacquer top coat. The key is ease of sanding and will seal end grain prior to staining…...specific example would be the end-grain tops of turned bed-posts. This prevents the bed-post tops from being darker than the total Headboard. If your using lacquer as your top coat in the home shop, as Bill says, just allow your first coat to seal and give it a good scuff sanding.

For the home shop; sealing with anywhere from a 1 to 2# cut de-waxed shellac as described by Karson above is the way to go. From a de-waxed shellac base, your final finishing options still remain open.

Neil


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## Karson (May 9, 2006)

Thanks Neil for your insight on Lacquer sanding sealer.


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## Treefarmer (Mar 19, 2007)

Very good info guys. This is so valuable. A good finish makes or breaks a piece and my knowledge is so poor you could type for a week and I'd stiil be finding out new things. I just followed what seemed to be the concensus on my chair. What about the use of oils? I put two coats of watco on then finished with shellac. I also poly'ed the arms. Does the use of the shellac on oil still harden the fibers the same way?


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