Sand-through with water borne lacquer

TEST ON SCRAP FIRST! If your question is about repair work, either regluing or refinishing, please post it in our Repair Section.

Re: Sand-through with water borne lacquer

Postby rob newell » Thu Feb 01, 2018 6:25 am

Mike, you say:

As Gordon says, the 400 grit sand is to knock down higher spots or brush strokes, and take care of any runs. With dry sanding and light pressure you can see where the high spots are getting sanding, and I try not to sand past when everthing looks dull.

Do you mean that between coats it is OK to leave areas of unsanded, shiny finish showing?

Cheers

Rob
rob newell
 
Posts: 7
Joined: Wed Jan 31, 2018 6:55 pm

Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Thu Feb 01, 2018 12:08 pm

Rob - that was my interpretation, and is the practice I followed on my latest effort. It certainly seemed to make no difference in the quality of the pre-final-sanding finish; each subsequent coat buried the shiny spots, and the next sanding revealed new ones. When I start the final sanding next week, the low spots from the final coat should disappear without any problem, if not with the 800 grit, then definitely at some point before I get to 2000.
==Steve==
User avatar
Steve Sawyer
 
Posts: 571
Joined: Wed Jan 02, 2013 2:20 pm
Location: Detroit, Michigan

Re: Sand-through with water borne lacquer

Postby Brian Evans » Thu Feb 01, 2018 1:53 pm

With a non-catalyzed or pre-catalyzed finish (most of the waterborne, one part finishes are one or the other), the new coat of finish will chemically bind or "burn in" to the previous coat of finish if you recoat within a few hours, or a day. Sanding is not required for that, and may even be sub-optimal in terms of building the layers of finish to a depth that you want to achieve. With a totally non-catalyzed finish like old school nitro-cellulose, a subsequent coat can chemically bond even after years of time because the finish never cures, it only drys. With a pre-catalyzed finish (like the Brite-Tone instrument lacquer I have been using) the finish drys in an hour or two, but does not "cure" for several days. If you re-coat before the cure has begun but after the coat has dryed, the chemical bond happens and the new coat burns in to the old. If you re-coat after the finish has cured (the catalyst activates, the finish chemically changes and cross-links the polymers, as I understand it - not a finish chemist!) then the new coat will not chemically bond but will only mechanically bond. Like epoxy, at that point you need a rough surface to let the new coat have mechanical teeth to grip to, and I would personally use around a 180 grit at the finest.

If the finish you are using has words like "pre-catalyzed", "cures" and "cross-links" in the description, most likely you have a pre-catalyzed finish that cures after several days and is problematic to re-coat after a full cure. I am not sure, but I think the finish that started this conversation - GF High Performance Top Coat - is not pre-catalyzed. They discuss re-coating after many days, top-coating many different kinds of old existing finish, and they sell an equivalent finish that is actually named "Pre-catalyzed". That does not necessarily mean that it can chemically bond with itself after many days, months or years like nitro-cellulose can. I find most finish manufacturers are far more interested in selling you something, anything, than selling you the right thing and educating you on what it is and how to best use it.

Brian
Brian Evans
 
Posts: 668
Joined: Sat Aug 30, 2014 8:26 am
Location: Tatamagouche, Nova Scotia

Re: Sand-through with water borne lacquer

Postby Barry Daniels » Thu Feb 01, 2018 2:19 pm

I use nitro and sand about every 6 coats. Each time I sand I see fewer low spots. I know that there are some folks who hold off on sanding until all coats are applied. But I think sanding during finish application results in a more level finish and less chance of sand through.
MIMF Staff
Barry Daniels
 
Posts: 1902
Joined: Thu Jan 05, 2012 10:58 am
Location: Houston, Texas

Re: Sand-through with water borne lacquer

Postby Mike Conner » Thu Feb 01, 2018 2:20 pm

rob newell wrote:Mike, you say:
As Gordon says, the 400 grit sand is to knock down higher spots or brush strokes, and take care of any runs. With dry sanding and light pressure you can see where the high spots are getting sanding, and I try not to sand past when everthing looks dull.
Do you mean that between coats it is OK to leave areas of unsanded, shiny finish showing?
Cheers Rob


Rob,
I look at the small remaining shiny spots as thinner areas, and that the 400 grit sanding is bringing the thicker areas down to that level.

As Brian has stated, the waterborne finish should chemically bond with the unsanded areas as long as the additional coats are applied before the cure has happened. You could always buff the shiny locations with a super-fine abrasive pad if you feel the gloss surface is a risk - but I haven't taken it that far.
//mike
Mike Conner
 
Posts: 127
Joined: Wed Feb 08, 2012 8:12 pm
Location: Seneca SC

Re: Sand-through with water borne lacquer

Postby rob newell » Thu Feb 01, 2018 6:55 pm

Thanks, to Mike and others who replied to my query. I appreciate it.
rob newell
 
Posts: 7
Joined: Wed Jan 31, 2018 6:55 pm

Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Sun Mar 25, 2018 6:14 pm

So sorry for letting this thread languish for so long, but I've gotten distracted by another project that I'm doing in parallel with this build (you'll see some new questions from me on that elsewhere), but I wanted to "close the loop" on this discussion.

The re-application of the finish came off good. Had no trouble with any witness lines, so it would appear that the GF HP is pretty forgiving w/regard to re-coat times. No indication that any of the subsequent coats had any trouble bonding with the earlier coats.

As suggested earlier in this thread, I was less aggressive in my sanding, shooting to have the last of the "shiny spots" disappear with the 2000 grit.

As you can see from the pictures below, I didn't sand-through this time. Finish isn't perfect, but for my second build if it comes out this good, I would consider it acceptable. What's interesting though is that if you zoom in on the edge of the highlight in the second pic below, you'll see some remnants of the cross-hatching that resulted from my changing the direction in which I applied each coat of the finish. This was a glaringly evident pattern when I began the final sanding, and my guess is that I should use a slightly firmer backing for the sandpaper (I have been using an old-fashioned pink eraser). I have some hard rubber that I think will be a better choice for level-sanding.

Finally, it looks as though I was damned close to sanding through at some points. Look at the third pic, a close-up that shows how the grain of the veneer started to telegraph through the finish in a couple of spots. Almost makes me think that the HP might result in a much thinner coat than the Enduro-Var, and thus might need more coats to get a good build.

Again, thanks to everyone for their encouragement and advice!

Test_Finish1.JPG


Test_Finish2.JPG


Test_Finish3.JPG
==Steve==
User avatar
Steve Sawyer
 
Posts: 571
Joined: Wed Jan 02, 2013 2:20 pm
Location: Detroit, Michigan

Re: Sand-through with water borne lacquer

Postby Barry Daniels » Mon Mar 26, 2018 10:31 am

The final photo shows evidence of some finish shrinking from additional curing after level sanding. Maybe wait a bit longer next time. The cross hatch in the second photo is a bit strange. I don't know what is going on there. Probably the same issue.
MIMF Staff
Barry Daniels
 
Posts: 1902
Joined: Thu Jan 05, 2012 10:58 am
Location: Houston, Texas

Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Mon Mar 26, 2018 10:56 am

Barry Daniels wrote:The final photo shows evidence of some finish shrinking from additional curing after level sanding. Maybe wait a bit longer next time. The cross hatch in the second photo is a bit strange. I don't know what is going on there. Probably the same issue.

Hmmm... waited a full week before doing the final sanding, but your observation makes sense. No reason not to wait a little longer next time.

I was also surprised to get that effect in the last picture considering I filled with three coats of epoxy (System Three Silvertip).
==Steve==
User avatar
Steve Sawyer
 
Posts: 571
Joined: Wed Jan 02, 2013 2:20 pm
Location: Detroit, Michigan

Re: Sand-through with water borne lacquer

Postby Gordon Bellerose » Mon Mar 26, 2018 4:39 pm

A couple of observations late in the game.

1. The cross pattern you see in the second pic, is most likely caused by the cross sanding pattern you used.
When I am sanding in between coats, I use a small circular pattern first, followed by going with the grain of the wood.

2. I find epoxy a great grain filler, and use it almost exclusively. It does require a bit more work to get it level.
I sand it down almost to the wood on each coat. I use 3 coats usually.
I need your help. I can't possibly make all the mistakes myself!
Gordon Bellerose
 
Posts: 1051
Joined: Wed May 30, 2012 11:47 pm
Location: Edmonton AB. Canada

Re: Sand-through with water borne lacquer

Postby David King » Tue Apr 24, 2018 1:34 pm

The finer grits of Mirka Abranet won't load up especially if you connect a vacuum to the block. However that "paper" isn't flat, it's woven and can leave ridges in the surface if you aren't very conscious of how you're moving it i.e. in swirls, not in straight lines.

Some of your grain sinkage may be due to the underlying epoxy coats which are extremely heat sensitive when power buffing. As the surface warms up the epoxy bulges out of the pores a little and then sinks back down a bit too far as the surface cools.
David King
 
Posts: 2412
Joined: Sat Jan 07, 2012 10:01 pm
Location: Portland, OR

Re: Sand-through with water borne lacquer

Postby Steve Sawyer » Tue Apr 24, 2018 8:47 pm

David King wrote:Some of your grain sinkage may be due to the underlying epoxy coats which are extremely heat sensitive when power buffing. As the surface warms up the epoxy bulges out of the pores a little and then sinks back down a bit too far as the surface cools.

That's good to know. I'm using a small 3" random-orbit polisher that I don't THINK produces much heat, but might be enough if epoxy is very heat-sensitive as you say.

Thanks!
==Steve==
User avatar
Steve Sawyer
 
Posts: 571
Joined: Wed Jan 02, 2013 2:20 pm
Location: Detroit, Michigan

Previous

Return to Glues and Finishes

Who is online

Users browsing this forum: No registered users and 1 guest

Your purchase from these sites helps support the MIMForum, but only if you start at the links below!!!
Amazon music     Amazon books     Amazon tools     Rockler tools     Office Depot    

The MIMF is a member-supported forum, please consider supporting us with a donation, thanks!
 • Book store • Tool store • Links • 
cron