Gluing Santos Mahogany
Gluing behavior of Santos Mahogany, and a description of potential allergic reactions. December 6, 2008
Question
We manufacture stair treads and have an order for some constructed from Santos mahogany. I understand that this material does not glue well. What type of glue should we use and how can we achieve a good glue line?
Forum Responses
(Adhesive Forum)
From Professor Gene Wengert, forum technical advisor:
The high density and some oiliness would make this wood somewhat difficult to glue with standard woodworking adhesives, but not as difficult as teak or other resinous woods. Surfaces should be prepared and glued within 15 minutes to achieve the best joint strength. It should not be necessary to clean the freshly prepared wood with a solvent before gluing. However, if there is a delay between machining and gluing, then the surface must be cleaned with a solvent. A fresh, clean surface can use any modern woodworking adhesive.
From contributor C:
I am not familiar with Santos mahogany. I came in contact with plywood and hardwood which was sold as Santos rosewood this past year, which was one of the most toxic things I have ever encountered. The sawdust was just as toxic as the sanding dust. Where the sawdust escaping the dust collector during a tablesaw operation got on your forearm, you would have a measles-like rash the next day, as well as around the perimeter of your dust mask on your cheeks and the hollows by your nose. Two to three weeks to clear up the rash and itch. Thorough research is in order and necessary. The Santos rosewood looked like a mahogany grain and I'm sure is a relative, so be careful what they are asking you to work with. Gluing it could be the least of your worries.
A surefire method of a good glue joint on difficult woods is perfectly fitted glue lines (no gaps when placed side by side), a gentle wipe with acetone, and a good epoxy. Call MAS or West Systems and tell them what you want to glue up.
From Professor Gene Wengert, forum technical advisor:
Many tropical woods do cause dermatitis reactions. Your description is typically what I hear. Santos rosewood is Machaerium scleroxylon, although sometimes some other species in the Machaerium genus may be included in the lumber sold as Santos rosewood. Santos mahogany is Myroxylon balsamum.
From contributor J:
We do a lot of work with Santos mahogany and have had very good luck with regular yellow wood glue. We even use a fast setting assembly adhesive on it with no problems.
From contributor D:
I've done a few stair jobs with Santos (man, I can almost smell it now...). I tried a few samples after my first glue-up attempts had mixed results. After making several samples, using different adhesives, some were sawn edges, some were jointed, and cleaning half of the samples with acetone first... I broke each sample apart, looking for the best joints. The acetone didn't help (but the samples were all glued within half an hour after milling). My results showed that a perfectly jointed board and yellow glue worked best for me. Santos is a very stubborn material, and a lot of it was twisted to some degree. Careful preparation is the key. This stuff likes to chip out when you joint it, and needs to be jointed slowly to avoid scalloping the edge. You may need to reverse the direction you're jointing to make things go smoother, yet sometimes the wood doesn't seem to want to be jointed in either direction. Also, a large tread job can easily trash your jointer blades, so you should constantly check the edge of your boards for any raised ridges due to nicks in the jointer knives.
