Post
by James Mc » Tue Mar 04, 2008 5:33 am
Hi Alan
I don’t have much experience in the guitar construction area but I’ve worked for antique furniture restoration companies doing repairs and traditional finishes and can give you some insights into finishing and gluing from that point of view.
Often after stripping back old varnish there are oil marks from where oil based polishes have soaked through chips or cracks and soaked into the timber. If they were really bad we would sand the surface with fine paper then give it a good soaking wash with metho and put it in the sun for a few hours to dry. If it helped but the stain was still too apparent we would give it another wash or two. We would then rub on a coat or two of shellac over a stained area, if the stain was about the same colour as the timber is wet, then it would often just disappear. If not then we would just stain the whole thing to hide the makes before polishing.
I’ve French polished furniture that has previously been finished with oil, i.e. tung oil or Danish oil. Just prep it like you would any timber for French polishing and away you go. Maybe because of the way shellac penetrates and bonds to the timber it displaces the oil or something. I have seen a disaster of a home restoration job where they prepped up a gorgeous old BZ rosewood dresser then had it sprayed with one of the new modern clear finishes. It looked great for a month or so until the new finish started to lift, probably because it had been previously treated with something like Danish oil.
Old timber mosaic tables can be a bitch for oil contamination under damaged tiles, but gluing in new or restored sections isn’t much of a problem (matching them to the existing ones is). To glue we would just give it a bit of a sand and scrape to remove any old glue then give it a good scrub with metho and steel wool. When you are ready to glue give it another light sand and a quick wipe with metho then once the metho has dried off glue in the new or restored section of mosaic with hide glue. I had doubts about the glue holding when I was told to do it this way, it was a shop job and there was no rush so I put it down the list to give me time to do a test. I grabbed a bit of scrap and soaked it with linseed oil then I wiped it off and put it on the window ledge to let it dry for a week. Then cut it in half and went through the sand metho sand process before edge gluing it together. When I tested the joint the timber broke but the join held.
It is nice to have confidence in whatever method you decide to use and nothing can give you that confidence like testing the method for yourself. So I think you should grab some oil soaked timber and test away.
Hope that’s of help.
James
