Resorcinol glue caution

There is a lot less Resorcinol glue being used these days and it is not even available from the usual sources under that name but rather called Cascophene.

I have a serious caution to offer about Resorcinol glue. I have had two propellers for experimental aircraft built in my shop in the last few years. The most recent was glued with Cascophene/Resorcinol from Aircraft & Spruce Co. It was a great disappointment. After gluing up a 6 board laminate of some expensive 6'X3/4"X7' maple (not to mention all the time and work) and making preliminary carving with our home made duplicator, we found that the scraps were separating on the glue line instead of in the wood. Almost all breaks were on the glue line with a film of glue remaining on both sides. This does to generate much confidence in the glue since we are experienced with gluing all kind of material and do not expect this kind of result. The glue suppliers as well as manufacturers were contacted and they have made some tests of both liquid and powder parts we sent in for their study. They have been very responsive and it looks like the glue was just old. Because of the inability to accurately trace the history of the glue, we are unsure of its age. Some more samples were made with old Weldwood Resorcinol that I know to been on my shelf for at least 15 years. The results of those tests with old glue mirror those of the recently purchased glue from Aircraft & Spruce. This kind of result from Aircraft & Spruce for such demanding and critical projects is very disappointing.

Do we trust this prop on a real airplane? The jury is out so far.

My advice is to not use any Cascophene, Resorcinol, or any other liquid/powder glue if the shelf age is not accurately known and the source trusted.

As a result of that experience I am thinking of experimenting with epoxy. The reason for not using epoxy in the first place is the probability of starved glue joints under the high pressure needed to get good mating of such big pieces of thick hardwood. I plan on trying a fabric fabric separator like Xnole and or sawdust to prevent dry joints. Pre-wetting with epoxy to a tacky state before clamping will also be done. If successful, this will also make assembly easier since glue shelf life, open time, working time and temperature is critical with Resorcinol and not very critical with epoxy.

Tom L

 

Sounds like the glue containers should be dated with the production date of the glue.

Another possible separator is monofilament fishing line. A quick search found sizes starting at 0.008.

 

Of course that is true and we expected to be able to pin down the age but so far, that has eluded us. Even tracking back through the various businesses that handled it. One of the problems related to repackagers is that such data gets lost.

 

Thanks for the heads up.

 

I use monofilament as a separator in highly pressurized joints too.

I've had some old resorcinol issues over the years too, but have long ago used only "known quantity" products. I haven't bought any in a few years, so sourcing may be an issue now.