Achieving a Smooth, Glassy Finish on a Burl Veneer Tabletop
The crazy grain and deep structure of a burl surface pose a special finishing challenge, and the choice of adhesive can also add a twist. Here, pros offer advice from several different perspectives. December 8, 2006
Question
I am currently building a small table that has a book matched myrtle burl veneer top. The substrate is plywood and the veneer is applied with contact cement. The top is edged with solid walnut. I am worried about getting a nice, smooth, glassy finish on the burl with all the swirling grain. The client is very picky. Any ideas for the best finish? This table has to be perfect.
Forum Responses
(Finishing Forum)
From contributor M:
If it needs to be perfect, then contact cement isn't the adhesive of choice. Too much exposure to problems and issues. Also, depending on the finish schedule you choose, the solvents in the finish will permeate through the thin veneer and possibly have their way with the contact cement. In my opinion, you don't want to take that chance.
As for the finish, I've done this before with a small table using highly figured kewazinga veneer in a bookmatch, and I also needed a high mirror polish. The finishing schedule called for a coat of boiled linseed oil, let cure a week, followed by four coats of ultra-blonde dewaxed shellac. Let that dry a day just to be sure, and sand with 600# paper. Then I applied fifteen light coats of spray lacquer, wet sanding every five coats with 600#. The lacquer was for build and to take advantage of its natural wet sanding properties.
The final three coats were a mix of 60-40% mineral spirits and alkyd resin varnish for a wiping formula. This final top layer let me escape the perils that would have normally affected the lacquer.
From the original questioner:
Thank you. Yes, I should have known better. Contact cement isn't the way to go. Just got lazy and there seems to be lots of literature to support contact cement. I actually have a vacuum system. Well, the new top is in the bag. I will try your finish on both tops, as I have till December to finish this table.
From contributor R:
You will get quite a nice grain fill by wet-sanding the oil with 400 grit paper. The slurry fills the pores. I'm not sure what contributor M was leading up to, trying to escape some kind of perils associated with lacquer. I'm not so sure, either, about a thinned down version of varnish that was applied over the lacquer. Seems to me that no type of chemical adhesion would take place between the varnish and the lacquer. The varnish just sits on top of the lacquer and will lead to adhesion problems down the line. Small projects like what you and contributor M are doing really look wonderful with a pre-cat lacquer finish that's buffed out. This not only looks great, it also doesn't cost an arm and a leg.
From the original questioner:
Well, that seems a bit simpler. I often use lacquer with excellent results. I have used it over tung oil and deftoil. I have never, however, put it over linseed oil. Linseed oil seems like it never dries, even the double boiled stuff. I do like the darkening effect it has on wood and I am kind of interested to see what it will do to walnut. I think I will make a test board and do some experimenting. Thank you.
From contributor R:
I should have been clearer - if you are hesitant to use linseed oil for this purpose, you can use other oils like Watco or Dura-seal, as they work fine. Trick is to keep the surface real wet. I have a cheap Black and Decker palm sander, 1/4 sheet, and I use it to wet sand the oils into the wood.
From contributor B:
Keep it simple. Ideally you should have used hot hide glue to lay the veneer, but that is past. Use some paste wood filler, then coats of shellac, to achieve a full filled coating. You know the drill - spray (or brush), then rub, spray, and rub. Or, if you prefer, use lacquer - no sanding sealer needed if you use something like Magnalac or Magnamax. Same deal, spray and rub, spray and rub. Do not spray full wet coats, as you will open the possibility of affecting the holding ability of the contact cement.
From contributor A:
Contributor M, you really need to find a better way to finish your work. You're spending too much time and material, and too many applications of coatings to achieve a high gloss finish. Rethink your entire finishing process.
From contributor M:
No, this isn't a particularly cost-effective method of finishing. I find that burl veneers are slightly more topographic than flatsawn veneers when they come out of my vacuum bag. Perhaps it's the nature of the grain structure, but I find that they require special attention as compared to other, plainer veneers. Especially when a high polish is called for.
Had the request been for advice about a less figured veneer, my response would have been different. So my finishing schedule, as described, was more for build and to establish a flat surface. I do not use this schedule as a habit, but occasionally - as with some burls - I go the extra mile to get the finish that I'm going for. Hence the recommendation, which works.
As for the perils of lacquer that I described, in my experience a bare lacquer finish is not as durable in a day-to-day office environment as I'd like. Perhaps that's a vagary of the lacquer I've been using - I've never used a pre-cat lacquer (I'm a one-man garage shop without a dedicated spray booth). I'm all for trying it - just haven't been there yet. So among the products that I've used, I've found regular lacquer to be far too abrasion friendly as a final surface. The alkyd resin varnish topcoats were laid down to provide a more durable surface that would hold up to coffee cups, briefcases, etc.
The wiping blend is every bit as effective as a full-strength blend - it's just a physically thinner layer after the solvent flashes off. So more coats are required, but it's easier to manipulate and flows out better than an undiluted coat. The mirror surface I got bears that out. It's not buffed or treated in any way. That's the final end result of just the wiping blend over my leveled undercoats.
From contributor B:
The Magnalac is a ML Cambell pre-cat lacquer. The Magnamax is a post cat lacquer. There are others, but I am most familiar with these. I spray a lot on Magnalac on lots of different things.
From contributor I:
Burls should be laid up as a 3 ply veneer. This eliminates the telegraphing and supports the wild structure of the grain. Use the vacuum bag and quality hard glue. Instead of the linseed or Watco oil, I would suggest that you try SW clear stain base concentrate and wet sand it in just like you are doing with your oil. This product is designed to be topcoated and you will not have to wait so long to spray on your finish.
From contributor D:
Because you used contact cement, I would advise against using an oil or stain base sanding slurry idea to fill grain. I believe that using that much oil to create a slurry will penetrate the veneer and cause problems with your contact cement bond.
Here's what I would do: Spray about 3 or 4 very light "mist" coats of your favorite sanding sealer, shellac, or other film-forming finish. This is to seal the veneer without spraying a wet coat that would soak through the veneer. Do a light scuff sanding with 320 for adhesion (don't sand through the sealer). Then, you should be able to finish normally.
On a burl veneer, you'll need lots of coats of a lacquer to fill and level, and you may run into maximum build problems with a lacquer. I would suggest using a 2-part high build polyurethane or, even better, polyester to develop a thick quick build. Polyester is the best for this - sands flat easily, and is a very hard, stable base that will not shrink back into the wavy burl grain later like a polyurethane will. For ease of finish sanding and buffing, you can topcoat your leveled polyester with a 2-part acrylic urethane. Check out the fine Italian ILVA polyester and acrylic urethane products distributed in US by IC&S in Lancaster, PA.
From the original questioner:
Just to let you all know how they turned out… I made a second top using resin glue and my vacuum bag. I finished both the same. First the Watco oil wet sanded with 400. I even bought a Skill palm sander for this (what a piece of crap - sure makes me appreciate my Ridgid). Anyway, lost track of the number of coats of lacquer. 400, 600 then 000 steel wool. Rubbed out with a finishing wax. Wow! Both tops are perfect - no sign of delamination. I will keep the one done with contact just to watch it long term. Thank you to all that posted.
