Epoxy will not stick to OAK

LAST EDITED ON Aug-09-04 AT 08:40 AM (CDT)
 
I have had some problems with my hard maple engine mounts smashing and the engine getting loose. I decided to use white Oak instead of maple on an airplane but first I did an experement and glued some oak to some plywood. After drying for 24 hours the 3/8 x 1/2 oak pulled right off leaving the epoxy stuck tight to the plywood. I tried again same thing. I tried CA glue it will not stick well to oak either. The oak is very smooth on all 4 sides it has been run through a wood planer.

There are two main types of oak - red and white - The red oak is definately a no no as it is porous. You can take a piece of it and blow cigarette smoke through a short length of it due to the openings. These openings will cause crushing of the fibers under compression and is the main reason it is not used in boatbuilding - the openings will allow water inside and it can rot from insides out and outsides in. White oak is a solid wood and would hold up to the crunching better but I dont understand your problem with the adhesion. I have used it in woodworking for years without any problem using an assortment of glues. It does have a slight tendency to warp and twist more than maple but in our small sizes that would be negligable. Is there any chance the wood is still wet ( uncured )? If that is a possiblity run the mounts throught your microwave for 10 minutes - let cool and do it again and that should dry any sizes we use. Any chance it was subjected to some sort of oily substance - especially if it was reused wood. Slickness should not affect if the epoxy has time to do its thing - maybe setting too fast.

Epoxy adhesives don't "wick" into the surfaces that you are bonding as well as other types such as CA or solvent cements. Epoxies are more dependent upon the amount of surface area and surface finish for bond strength so you can improve the bond strength by roughing up the surface to provide some "tooth".

Also Bill made an a comment in his post that is pretty important. Generally, the faster the cure rate of the epoxy the more brittle the bond and the less time it has to flow into the surface imperfections of the surfaces. So use a slow cure epoxy and sand the bonding surfaces with 80 grit and let us know how that works.

Also, is your epoxy "fresh"? The stuff has a shelf life; about a year, unless it gets too warm, then it's less.

If you do try oak again for MM stock, be sure you drill the holes true and a bit oversize; oak has a slight tendency to split along the grain if stressed internally. But Hard Maple is so good, and so inexpensive, why experiment, unless you're looking for something lighter?

A question that needs to be asked. Is the oak varnished?

Epoxies will stick even non porous materials. You can glue a golf ball to a coke bottle with JB Weld.

A little trick documented by Bob Hunt on his video on the fuselage construction: use your jigsaw to add little sawcuts (say 1/16") deep, on the edge of your engine mount where it will be glued. This will increase the bonding surface area considerably.

Epoxy makes a mechanical bond, help the mechanics!

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"The optimist sees the rose and not its thorns; the pessimist stares at the thorns, oblivious to the rose." -Kahlil Gibran

A few decades ago when I was a Shipwright's apprentice the Old Master of Wooden Boats Earl Wakefield said "not all glues & adheaseves will work on Oak''

How about trying "Gorillia Glue". I used it to glue some Cocobolo wood together. The Cocobolo wood is one the the most dense and hardest woods known

I don't know about the epoxy problems,but I solved my motor mount crushing problems by using aluminim pads under the engine.Just be careful about tightening as you may break the blind nuts.I've gone to brass inserts to solve that problem.

I've had some luck with oily woods like spruce by warming the surface and the epoxy first. Thins the epoxy and helps it penetrate better. I'd use some 15 or 30 minute epoxy for this as well. The 5 minute stuff is somewhat different chemically, and not as strong as the slower setting epoxies. If you can, clamp the pieces being glued until the epoxy reaches full strength, which is actuall at least 24 hours.