Better woods with epoxy?

[Alixander Beck]

I am going to be laminating some frames and was wondering if there was a difference in epoxy bonds with difference species of woods? I have worked with mahogony and cedar mostly so my variance in species is not exceptionally diverese.

specifically thinking about the difference in bond strengths of of the common 5 woods: cedar; mahogany; maple; oak; teak used for a rib section about 5/8" in thickness and which might be suited best for ease of work and wallet. This is for a dinghy so I don't think strengh will be an issue. I'm leaning heavily towards cedar as it's light and easy to work with.


thanks

[SeaSpark]

The woods you mentioned will bond well with epoxy, except for the teak as it contains mineral oils. Teak must be rough sanded (50 60 grid) and "degreased" with acetone before bonding. The solvent must be dried 15-60 minutes before pre wetting with epoxy.

Info from pdf here:

http://forums.boatdesign.net/showpos...8&postcount=11

Note the info in the quote about aluminium bonding is not totally correct.

[frosh]

I have used epoxy glue with Western Red Cedar many times and found it completely successful. On a proa, I built curved crossarms out of four thin beams of cedar laminated together to achieve the S shape I wanted.
Under really big loadings the crossarms have remained as good as the day they were completed. If your boat is fairly small, there is little reason to use a heavier timber than WRC anyway.

[PAR]

The oily woods, or species that have particularly acidic qualities about them (like some of the oaks) will cause problems with epoxy bonds. There are techniques to improve the bond, but much depends on the application, laminate thickness, species and orientation in the laminate.

Teak is an oily wood, which can affect the bond, if the oil isn't removed, just prior to the saturation coats of untickened (or penetration coats) of epoxy.

Traditional oaks used in boat building are generally acidic, which will stop or severely retard the curing process in epoxy. Again this acid (tannins in the case of white and live oak), can be used to advantage as I found once when placing my hand in some still wet goo and having only a glass of orange juice to neutralize the epoxy reaction. It worked and the epoxy came off my hands with a paper towel.

Also using heat to best course will help offset some of the bond issues in more difficult woods. If the wood is warmer then ambient temperatures, but is cooling down (very important), ditto the epoxy, during application, the cooling wood will draw in the epoxy, much deeper into its fibers then if done at room temperature, which effects a better bond.

Laminate thicknesses need to be kept thin on these types of wood. On white oak, when laminating frames, for example, I'll do 5/16" thick "lifts", no thicker, to insure it gets good and stuck under epoxy, without the internal stresses in the wood fighting the bond or glue line.

I also use an aggressive "tooth" (36 grit or rougher) on these species, to provide additional bond help.

If you log onto each epoxy manufacture web site, you'll get application specific information about their offerings. Most of this information will apply to other epoxy brands as well, but some recommendations will be brand preferred, such as compatible stains and paints.

Personally, I wouldn't use teak in a "rib" or other framing applications. It's not as hard and is more brittle then most folks think. Some far eastern boats have been completely built of it (I've owned a couple), but it's not my idea of an excellent framing hardwood. I'd use it in a restoration, if I was forced, but other wise would prefer something tougher for the weight.

On your 5/8" frames (ribs) I'd use 3/16" laminates (3 pieces tall) with the glue lines providing the remaining thickness (two, 1/32" joints). This is a pain in the ass, but it insures the oak gets good saturation. You could also use two 1/4" laminations, with two 1/16" glue lines, but that's a lot of glue line to control.

In any case you'll likely laminate thicker, then mill down to your needed molded and sided dimensions.