How Many Times to Sand During Finishing

Finishers discuss when and how often to sand when spraying multiple coats of waterborne finish. December 2, 2009

Question
Years ago, I was taught by a former employer to seal everything with 2-3 coats, then sand once and topcoat. That is how I have been doing it for years and never gave it a second thought (using solvents). Now that I am using waterborne finishes, I don't think that system will work. It requires way too much sanding. The other day, I gave some pieces 3 sealer coats and 1 topcoat, and lightly scuffed after each coat, and got a beautiful finish, and I think it was just as quick as sanding only once at the end like I was doing before, since it didn't take so much elbow grease to get it smooth. I am just curious how much everyone else here sands, from the first sealer coat until the final coat.

Forum Responses
(Finishing Forum)
From contributor T:
I am sure the finish we have been getting comes from sanding between each coat. I have not come across anyone using 2-3 seal coats before the topcoat application. Seems to me your finish is not going to be as hard and may fail at some point.

I know I am on a learning curve when it comes to CV, but with a pre-cat lacquer I have several years under my belt and will stick with sanding each coat, 1 seal, 2 topcoats at 3 mil.


From contributor G:
Solid or clear? What are you sealing with? I've seen 2 primer coats, sanded after the first then topcoated in solid color. Also seen stain, shader coat, sealer, sand, topcoat with clear, but that was using self-sealing lacquer. Those were in solvent base, however.

From the original questioner:
My schedule looks like this on stained wood:

1- stain (spray and wipe with Woodsong)
2- seal with sealcoat
3- sand
4- seal with Aguabarnice
5- lightly scuff
6- seal with Aguabarnice
7- lightly scuff
8- topcoat with Aguabarnice

Does this schedule look like too much work, or is this the kind of schedule required to produce a good finish with waterbase?


From contributor J:
You could skip the sealcoat, as the Aguabarnice is self-sealing. Then spray just 3 total coats of Aguabarnice as you are doing. Other than that, your schedule looks correct. I use a 320 grit sponge for sanding between coats. Works very well as they are less likely to burn through at the edges.

The only time you should need to use the sealcoat is if you need a barrier between something that may be incompatible with the Aguabarnice or if you want the ambering from the sealcoat. In that case you would spray 1 coat sealcoat and 2 coats of Aguabarnice.


From contributor A:
Your former employer thought he was saving some time by not sanding. Imagine your substrate (stick of wood/plywood) as having highs and lows (mountains and valleys). When spraying, the finish evenly covers the highs and lows. Your old boss thought that if he applied numerous coats in succession he would fill up the lows with finish. This does not happen.

It doesn't matter if you sand once or twice, you still have to take off the same amount of finish to achieve a smooth/flat final coat. Even if you do the flawed "fill method" you will still have to start with 240 grit to remove a bunch of material, then switch to 320.
The one topcoat method is not a good idea either. It is hard to achieve a decent film thickness in one coat. If the finish is self sealing and thick you can get away with 2 coats.


From contributor A:
We all posted at the same time. You are calling your first 2 coats of AguaBarnice "seal coats". Only the first coat is referred to as a seal coat. The rest are first, second, etc. As long as you are starting with sound surface, scuff sanding with 320 paper or maroon scotchbrite works fine.

From the original questioner:
Thanks for all the input. I have been using sealcoat just because I like the look it gives on stained wood, and it seems to help with grain raise on the first coat of waterborne. Between using sealcoat and adding some Transtints to my Aguabarnice, I really got this finish looking like warm amber nitrocellulose lacquer.
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