Sanding sealer

[Gregor1]

I am finish sanding my glued up panels in preparation for milling. After that, should I use sanding sealer before applying wipe on polyurethane? Can you get wood, oak and walnut, too smooth for finish? I am final sanding with 320.

Thanks  Greg

[jteneyck]

I am finish sanding my glued up panels in preparation for milling. After that, should I use sanding sealer before applying wipe on polyurethane? Can you get wood, oak and walnut, too smooth for finish? I am final sanding with 320.

Thanks  Greg

Sanding sealer is a way for companies to separate people from more of their money.  To me, the only time a sanding sealer is of any benefit is if your topcoat is waterborne and applying it to the raw wood will cause a lot of grain raising.  In that case, I use Sealcoat shellac first as a sealer to prevent the grain raising.  

Can you get the wood too smooth?  Yes.  If you are using a film finish there's no benefit, and the potential adhesion problems, in sanding beyond where you can no longer see the scratches, typically 150 grit but maybe as high as 220 with some woods.  For oil finishes, sanding higher does have benefit and I don't think there's any upper limit although at some point it's of no further benefit.  

John

[Willyou]

If you are using a soft wood, sand through 220 grit. If your using a hard wood, 180 is enough. Then apply your first coat of poly and let dry. Then sand with 220-320 to remove any raised grain or dust nibs. Apply remaining coats sanding between coats as with the first. It you want a fine polish after the last coat, start with 600 grit wet/dry using a cork or smooth rubber faced block by hand and use water to lube. Work through 2000 grit wet/dry. Wax if you like. If you are going to do the final polishing, make sure you have enough film thickness to accommodate it.

[Bill Tindall]

I am finish sanding my glued up panels in preparation for milling. After that, should I use sanding sealer before applying wipe on polyurethane? Can you get wood, oak and walnut, too smooth for finish? I am final sanding with 320.

Thanks  Greg

The first coat of many finishes results in a rough surface that needs smoothing.  Some top coats do not sand well without gumming up the paper, lacquer for example.   In these cases, a sanding sealer is applied that has additives than enable it to be sanded without loading the paper.  When I sprayed lacquer I always used a first coat of sanding sealer. The conversion varnish I spray more frequently sands without loading paper so I never use a sealer under it. There can be a reason to need a sealer in some situations other than to aid sanding but that is a more involved discussion.

There is no economic disadvantage to using a sanding sealer.  It simply substitutes for a layer of something else and it is often cheaper than the top coat.  Many of the urethane varnishes sand acceptably with stearated paper ( I use 360 or 400 grit whichever I can find).  If what you are using sands acceptably then a sanding sealer is unnecessary.  (Shellac is an excellent sanding sealer.  I use Zinser because it is cheaper, convenient and stabilized to have a long shelf life)

Where to stop sanding depends on what happens next. I stain walnut and oak.  I find the staining result is best when I stop sanding at 180 for these woods.  I usually stop at 220 for stained cherry.  I have made on the order of 100 major pieces of furniture and never had need to sand the bare wood past 220 for any.  I start at 120 if I can.  If 120 is too slow then the progression will be 100, 120, 180.  I find it difficult to remove 80 grit scratches so I avoid starting at 80. If I needed 80 to remove something I will instead use a scraper or hand plane.  

I follow the 80/20 rule. Spend 80% of your sanding effort on the first grit and 20% on the rest.  Sanding defects reveal a beginning woodworker.  When sanding look for dull spots.  These spots are dull because they are torn grain and catching sanding dust.  They will similarly catch stain and result in a dark blotch. Sand the first round until the surface looks perfectly uniform in good light.

[MichaelMouse]

I am finish sanding my glued up panels in preparation for milling. After that, should I use sanding sealer before applying wipe on polyurethane? Can you get wood, oak and walnut, too smooth for finish? I am final sanding with 320.

Thanks  Greg

No and no.  Seal with a cut coat of your poly after a 320 (CAMI) sanding and wiping along the grain.  Power sanders and people that press on them can heat and case-harden the surface of woods with close grain, which causes them to reject stain, and unthinned surface sealers.  Oak and walnut are so open that 220 or less (CAMI) is all they require with the grain. 

After your seal, sand nibs or embedded dust with that 320 and put on full-strength coat(s) smoothly.

[jcclark]

I personally love sanding sealer,
It's much cheaper than my final finish so it saves money.
It's also much easier to sand and doesn't gum up the sandpaper
like the final finish.
And it cures faster saving time.

[jteneyck]

I personally love sanding sealer,
It's much cheaper than my final finish so it saves money.
It's also much easier to sand and doesn't gum up the sandpaper
like the final finish.
And it cures faster saving time.

Every finish system is different so that might work best for you.  For most of the WB's I use they dry as fast as sanding sealer and sand just as easily.  Sanding sealer costs marginally less but having to have two cans of finish eliminates any cost advantage until you use enough to cross the breakeven point.  If you use WB products look at GF's Enduro Clear Poly and TC's EM-6000 if you have not already done so.  

John

[Wildwood]

A good short article on sanding sealer. Tells you what it is & when to use it.

https://www.rockler.com/learn/when-to-us...ing-sealer

[jcclark]

I use conversion varnish with a vinyl sealer, both are 2K products (use an activator).
I buy gallons of this stuff and won't ever go back to a 1K product again.
My sealer is $43.00 a gallon, which I think is pretty good.
The 2K products are quite different than the "use out of the can" 1K products
so there are different results.