Replies

1. 
   Lar55 | Feb 08, 2003 06:48am | #1

   Dan,

   Since you would like to keep the natural color of the wood, I would apply a couple of coats of a Polyurethane OR a couple of coats of a clear varnish.  I'd recommend  getting  the book "Hand-Applied Finishes" by Jeff Jewitt.

   Lar

2. 
   RLMillard | Feb 08, 2003 03:58pm | #2

   The natural color of mahogany will change dramatically with time, and I know of no way to stop this process. You could slow it down with a spar varnish that has UV protection, but these stay somewhat flexible and are difficult to rubout, to an even sheen. I work with mahogany almost exclusively, but I also dye it to match the period reproductions I make, but the following is what I would do. Before committing to this, I would give the piece a quick rub down with a rag soaked in mineral spirits, to see how you like the look. Mahogany has terrific reflectivity, but this is a double edged sword. It makes for stunning grain, but if not taken in to account it can result in a less than satisfactory look. Think of it as carpet, when viewed from one direction it looks dark and the other, it looks lighter.

   Sand to 320 grit, and apply a very thinned down coat of de-waxed blond shellac. This wash coat will prevent or reduce the effect of any splotching caused by the following coat (s) of oil. Scuff this and apply boiled linseed oil with some Japan drier added to it. Apply the oil hot ( watch out this is not the safest thing you can do). Apply no more than two coats of the oil, and let dry for 10-14 in a warm room, or until you can‘t smell the oil. On the top, I would apply grain filler, that has been tinted to be slightly darker than the wood itself, so that as the mahogany darkens you won’t end up with lighter pores. Then coat with Behlens Rock Hard varnish for the top, and shellac for the base. The varnish is very durable, but it is a real pain to rubout , being prone to the halo effect of sanding into a previous layer, since they do not melt together like shellac/lacquer. If you wanted to you could skip the filler and just apply many coats of the varnish carefully sanding back to fill the grain, but this method requires considerable time, as the varnish dries slowly. Using shellac for the base is the way to go, since it is easy to apply and rubout, and is very durable for these low wear areas.

1. 
   DJBPS | Feb 10, 2003 06:24pm | #3

   Thanks for the responses!. This is much more detail than I ever expected to receive and really shows the skill level of the people that use this forum. Once again I appreciate it.

   Rob, I think I understand everything you've suggested but, being a true novice, I had a couple of other questions for you:

   1. I'll be doing the finishing in my workshop (garage). I'm in Canada and while the garage isn't really cold, it's certainly not "warm". Will this have a significant impact on anything?

   2. You mentioned that the Behlen's is difficult to apply. I'd hate to get to that step and then screw it up. Are there other options that will be a bit easier to apply?

   Thanks again for your help on this.

   Dan

1. 
   RLMillard | Feb 11, 2003 03:39am | #4

   A cold or cool space will significantly slow the cure time of oil, and may prevent the curing of the varnish .

   I have been using Rock Hard Varnish for quite awhile, and my method continues to evolve, but here is the current process I use. I use the varnish full strength for every coat. I sometimes set the can in a pan of warm water to improve its flow. Never brush from the can. I ladle some into a plastic cup and work from that, discarding any that is left over. I use Badger brushes or an oval China bristle brush by Omega.  Brush cross grain first and finish by “tipping off” with the grain

   Apply the first coat and let it dry 36 hours, and sand with 220, either with a RO sander hooked to a vac, or by hand . The sander is quicker, but takes a light touch to avoid a sand through. Then apply one coat each day, sanding after each one, to level out any brush marks and remove dust specks. This repeated sanding is important, since the layers do not melt into one another, and sanding into a previous layer, will leave the dreaded “witness marks” which are impossible to remove, and requires recoating the piece. The last coat, needs to be done carefully, being sure not to miss any areas , and be left where it can dry as dust free as possible. I apply 4-5 coats, over filled grain. Over open grained woods, you may have to apply double that number . After a curing period of at least 14 days, start sanding with 400 or 600 grit paper, using mineral spirits as lubricant . I use an art eraser as a sanding block, this may seem to be way to small, but it gives you excellent control. Sand methodically until you get an evenly dull surface. Then sand up to 1500 grit, being sure not to skip any grits. Once you have the surface uniformly dull, the rest of these grits will go very quickly.

   Now switch to a felt block with a mixture of I part 4F pumice, to 2 parts rottenstone ( just do this by eye) , and rub using mineral oil as a lubricant. After a good work out, your top will have a deep even sheen.

   I now use a Milwaukee automotive buffer and Behlen’s buffer polish to speed things up. With this method, I sand to 1000 grit and buff to a high shine, and cut this back with pumice/rottenstone , to a even sheen . The buffer will also allow for a shorter drying time of the varnish. On a recent project I got side tracked and did not get back to the rub out for over a month. This taught me that the longer the varnish has to cure the easier it is to rub out and the better the results. I’m now going to let my varnish sit for 3 weeks before the final rubout, but I will do the sanding at 10 days, this way if I encounter a problem, like a rub through, I can recoat and start the clock from there instead of at the end of the 3 week period.

   A fellow woodworker, who’s judgment I trust has given up on varnish, and has gone to polyurethane , and says the results are indistinguishable from varnish. The poly dries quicker, is not as finicky about application temperature and is probably more durable. Poly will leave witness marks, just like the varnish, so the sanding is necessary. I just have an irrational aversion to using poly on my period reproductions.

2. 
   DestinDave | Feb 11, 2003 04:59pm | #5

   Desks really take a beating and are subject to finish degradation from contact with skin oils and sweat (maybe not in Canada) and for that reason I'd suggest urethane varnish which is very durable. I use my mouse directly on my top without pad! Heat, or lack of it, affects cure time. For varnish to cure optimally, temp should be minimum of 60F.

   Another option is to varnish the top and use an oil on the sides, particularly if you're not skilled with a varnish brush. With varnish, I would do only one side at a time, turning the desk so that side is horizontal. Aoiding sagging on vertical surfaces with slow curing varnish in the cold is a serious problem that can only be avoided by keeping it horizontal.

1. 
   DJBPS | Mar 06, 2003 10:49pm | #6

   I just wanted to thank everyone for their responses. It's given me a much better idea of what I need to do.

   Thanks,

   Dan