Sanding Steps in the Glazing Process

      When creating a glazed finish, does sanding between coats help, or hurt? March 28, 2008

Question
This is my first attempt at glazing (alkyd base, wiped on and off) over a white pigmented vinyl sealer. What should the final sanding grit be so as to not leave scratches that the glaze will stick in? I feel that I will have to sand a bit on the final coat to level it out perfect. So far, I have done one coat, sanded with 240, and now sprayed the second coat, which I am planning on sanding with 320. It looks like it will take a third coat. Should I use 400 to level the third coat, then a scothbrite before the glaze? I didn't need to level the final coat on a sample piece I made, but I am getting some overspray, rough places, etc on the full size pieces that will need to be fixed before glazing. Any suggestions?

Forum Responses
(Finishing Forum)
From contributor R:
I don't sand my final coat prior to applying a glaze since any scratch pattern will grab the dark glaze and show up as a dark scratch. Maybe, just maybe, you can gently drag a white scotchbrite pad over the large areas just before you apply the glaze. As you have progressed throughout your project, have you made up some sample boards that might give you an idea on just how much you can clean up the surface before it shows the dark glaze in the scratch patterns? If I was you, I would try and make my surface as smooth and as dust free as possible without having to sand the last coat.



From contributor T:
I generally try to make my second coat (or third coat, in your case) as smooth as possible, therefore, I don't have to sand it. My vinyl sealer doesn't like to flow out, so I thin and heat it on all coats.


From contributor P:
Don't sand. You want them as smooth as possible. We just completed a large glaze job and it looked great!


From the original questioner:
It seems that I am not getting a really flat finish off the gun without any sanding, though. Won't any discrepancies be highlighted with the glaze? I realize that sanding will cause its own discrepancies, but I was thinking that if I sand at a high enough grit, then scotchbrite that, the glaze won't pick that up.


From contributor J:
You might be able to find a high enough grit if you get into micron paper, but you are just making more work for yourself. Concentrate on getting a smooth finish off the gun on your last coat of sealer before glazing. Some retarder in that last coat may be in order to help combat the overspray and help it flow out better.


From contributor R:
I think a 400 grit is more than enough and if you wish to go up to 500 that is okay. Remember the sandpaper leaves small scratches that you can not see, and with the 500 grit you won't see the difference.


From contributor E:
Why are any of you glazing if you don't want the glaze to stick? Why not just do a light shade and make it look like glazing? Isn't glazing supposed to highlight areas of cut-throughs, depressions, and hang up in areas like corners and profiles?

Also, I would really like to know how good is your adhesion if you don't sand between coats and put a glaze on? Glazing is a weak link if this is a concern.



From contributor I:
He is going over white, so the scratch telegraph could be an issue. But the other tools leave their footprints as well - brushes, sheeting, cheesecloth and such. I almost always sand at 320, but am using the glaze as more of a contrast stain to pick up the pores and carving/turning details than using it to tone the surface overall. Mild scratches, brush smears, faint rag tracks and small spatter have always been "part of the look." We don't know what the goal is here though.


From the original questioner:
Thanks for all the replies. I tried a sample with my intended sanding schedule and it didn't work like I thought it would. I had a 2x3 section of plywood with the white vinyl on and left 1/3 as it was/off the gun, sanded 1/3 with 320, and the last 1/3 with 320, then 400, then a scotchbrite. The two I sanded definitely had a better sheen, but I had to remove more glaze overall to get the pigments out of the scratches, leaving the surface too white for the "dirty/antiqued" look I am trying to achieve.

So that put me back at requiring a better off the gun finish as most of you recommended. I experimented with different thinning ratios (the instructions recommend a max of 10%) and was able to get it to lay down flat enough to be acceptable.



From contributor R:
If I do an opaque finish, say an off white with a raw umber glaze, I try to get as smooth and as dust free off the gun finish as I can. I always apply the glaze over a clear coating, which I have applied over the opaque color. Sanding either the clear coat or the opaque coat would only allow the glaze to telegraph into the scratch pattern. After the glaze coat has been applied and manipulated to the look I'm after, I apply a clear coat over it. That binds the glaze to the coating underneath it and protects the glaze coat with the clear coating on top of it. I then proceed with my topcoats being careful not to exceed any mil thickness issues.

So, for an opaque coating, we're looking at:
Vinyl sealer (thinned coat, sand well)
Prime (full coat, sand real good when dry)
Color coat (full coat, no sand)
Clear coat, thinned (no sand)
Glaze
Clear coat, thinned (light sand)
Topcoats X2 (no sand between)

Keep in mind that it's not how much product you spray on, but how much you sand off.



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