Wash Coats Under Waterbornes

      Will a shellac wash coat eliminate a sanding step when finishing with waterbornes? Probably not. December 23, 2014

Question
I do 100% wb finishing using General Finishes Enduro line. I want to know if using a wash coat of dewaxed shellac before staining will put me ahead of the grain raise problem. I am trying to eliminate one sanding step, but if I have to scuff the shellac before staining then itís a moot point. Also, if I have to take another step in sanding the raw wood (pre-wetting) say from 180 to 220 the point is useless. Right now I have to do two if not three sandings to get the smooth/level look of a solvent finish.

Forum Responses
(Finishing Forum)
From contributor M:
The washcoat of shellac will probably still raise some grain, and it will also likely significantly alter the color/pattern of the stain itself (lighter color, and less grain definition). The easiest way I've found with waterborne finishes (SW KemAqua and Campbell Agualente) is to spray a very thin first coat after staining. I used to thin the first coat 20% with water and spray it "barely wet", and it sanded easily enough that the second coat looked pretty nice. Hardwood products were a touch trickier for some reason, but this still seemed to work just fine.



From contributor N:
I'd forget the shellac wash coat as a wb stain grain raise deterrence. In my experience when you've applied enough shellac to keep the grain raising at bay you've usually applied to much for your stain to penetrate and color the wood as you would like. I go with the pre-wetting and 220 sanding (usually I do this only on open grain wood) and sadly even then I still get some grain raise after staining but to my mind the results are still worth the extra effort.


From contributor A:
Sealcoat is wonderful stuff for the mostly waterborne finisher. It does grain raise like most any finish. However, once you sand it it will not raise again, which is possible when using waterbornes. I used ML Cambell and Targets products. None of them had grain raise issues. The best part of Sealcoat is it pops the grain. It is also great to use with Transtint dyes.

From Contributor M

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A wash coat shouldn't raise the grain at all. It will however isolate all the stray wood fibers and will feel like the grain is raised. Just a quick wipe down with a red Scotch-Brite pad should be fine and take very little time.


From the original questioner:
As stated above Iím trying to avoid one sanding step and still get the smooth build that you get from a solvent finish. If all the shellac does is freeze the grain Iím ok with that. If it is necessary to scuff it before staining then I am back at square one. I have tried the light coat method and all it does is cause the need for more coats. Maybe what Iím asking for does not exist?


From contributor D:
What about sealing your stain with SealCoat instead and ether using your WB topcoats. Also solves any adhesion issues to alkyd stains.


From contributor N:
I think you got it. There's just no magic bullet. WB needs lots of elbow grease, 400 grit and one more coat to approach (and still not quite get there) the look and feel of a solvent CV finish. When I show my customers samples of my standard WB finish (Target 8000) next to my standard solvent finish (SW F-3) they always (yes, always!) choose the solvent CV finish.


From contributor L:
As long as were on this subject. I really like Zinsser sealcoat. I read on this site or another a few months ago that regular shellac will not hold up to water but a de-waxed shellac like sealcoat will do much better than regular shellac. Is there any truth to this?


From contributor A:
Regular shellac is actually quite good at resisting water. The wooden boat builders that do restoration use very thick shellac as a glue/sealant around screw holes below the water line. My personal favorite example was priming cedar flower boxes with BIN white shellac primer. My wife was supposed to topcoat but didn't do it for 1 1/2 years. Dirt, water and flowers were in direct contact with no peeling whatsoever.



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