I’m not what you would call an accomplished woodworker. I’ve tackled
modest projects such as clocks, coffee tables, etc. My latest is the
federal card table that was written up in a past issue of FWW.
I finished it with several coats of polyurethane. I sure that
there are probably better finishes for mahogany than polyurethane
but poly is the one that I’m familiar with.
Given that this is winter, I tried using a brush but it causes
too many bubbles. I don’t recall that being the case back in the
summer. A simple cotton cloth seem to work well and not cause bubbles
and you don’t run the risk of a brush hair embedding in the poly. I
was wondering what are your experiences with poly? (Mine was the
MinWax version available at the home center). Also, I’m using finer
and finer grit in between coats.(120, 220, 400) Is there a better way
to do this? I’ve wound up with a fairly good finish but was wondering
what experiences others have had with poly.
Jim M.
Mt Juliet, TN
Replies
If you are having trouble with bubbles the varnish needs to be thinned. It doesn't matter whether the label says not to thin. The manufacturer just says that for regulatory reasons, they don't mean it, and those regulations don't really apply to you anyway. The fact that you didn't have the problem in the summer may be due to additional warmth making the varnish thinner.
Its too bad you have started with poly. Steve Latta who wrote that article recommended shellac and that would look much better. So too would traditional resin varnish. Poly is a bit less clear, and it doesn't sand or rub out as nicely or as easily as traditional resin varnish. Poly's extra abrasion resistence is hardly a factor on a high style card table, unless you expect people to walk on it with their shoes on. Behlen's Rockhard would look quite good on the top of the table, with shellac on the rails and legs.
Wood which will have a film finish on it doesn't need to be sanded finer than 180 or 220 grit. Between coats of varnish all you need is 320 grit. The only time you need to go finer than 320 is when rubbing out the final coat. After the final coat has fully cured, (a month for varnish a week or so for shellac) dust nibs can be removed with a light application of a card scraper. Then sandpaper, starting with 600 and going to 1200, followed by subricated steel wool (for a satin finish) or rubbing compound or rottenstone for a more glossy surface, which would be appropriate for a table of this style.
Hi Jim,
I, too, started with polyurethane varnish. In a past posting in the old Knots, someone noted that David Marks is now using a commercial product rather than his own recipe. Here is the link http://www.djmarks.com/stories/faq/What_is_the_mix_ratio_for_the_Linseed_Oil_Tung_Oil_and_Urethane_46687.asp
I did a test on a walnut board with a nice grain figure. On one end I applied seven coats of Minwax polyurethane, aggressively sanded between coats. The final finish just barely shows the wood pores, my preferred "look." On the other end I applied Marks' method. Everyone that sees the sample cannot tell the difference in the quality of the grain (i.e. "popping the figure"). Also neither end can be scratched with a fingernail. For most purposes, there is no difference (barring people walking on it).
I got the same result (no difference between the finishes) for bird's eye maple veneer.
The advantage of Marks' method (and most other wipe-on finishes) is that instead of removing excess finish by laborious sanding, you simply wipe it off. Long ago I ran out of cloth rags, now I use shop towels for wiping off the excess.
Test it for yourself on a piece of scrap from your project. BTW why not post your card table in the Gallery?
Edited 1/12/2006 10:35 am by JohnH
Hi
Thin the poly down with about 20 to30% naptha.or warm in a bouble boilerto about 90 degree F. Use a foam brush insted of a bristle brush. Works good.
Have a nice day Lee.
Steve has given you good advice. The only thing I would add is to be sure that the wood, finish and the air temperature is above 55 degrees and stays there during the curing process. The drying time on the label is based on 70-75 degrees and 50% relative humidity. Temperatures between 60-70 degrees will almost double the curing time and can cause more bubbles because the viscousity of the finish is increased. Temperatures below 55 may prevent the finish from curing at all.
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