Problems with TBII and basswood

[neil_w]

I've now had problems with using TBII to glue basswood in three different builds. In each case, the joints just weren't that strong. I have had no such problems with balsa.

Has anyone else ever experienced this? The whole "glue is stronger than the wood" adage certainly hasn't held true for me so far. I'm not sure what I could be doing wrong.

 

[Buzzard]

Plywood is less porous than balsa, so the glue does not soak in. With plywood or thin G10, I normally use a razor saw to cut numerous slots 1/32-1/16 deep on the root edges to give more "teeth" for the glue to attach to. Also, glue does get old if it has sat around opened. I usually have to replace my bottles after awhile.

Chas

 

[rharshberger]

Basswood not plywood.

Not sure why you are having that issue Neil, sometimes it helps to thin the glue just a bit to get better absorption. With the exception of oily woods TBII has been my go to glue for most most every wood to wood or wood to cardboard bond for many years in both rocketry and woodworking. Are you using any method to provide pressure between the two pieces, its usually required to get the best glue joints with wood glues.

Plywood is less porous than balsa, so the glue does not soak in. With plywood or thin G10, I normally use a razor saw to cut numerous slots 1/32-1/16 deep on the root edges to give more "teeth" for the glue to attach to. Also, glue does get old if it has sat around opened. I usually have to replace my bottles after awhile.

Chas

 

[Tobor]

I answered this question in your Alcubierre Build Thread (here).

 

[neil_w]

I'm gonna take the liberty of reposting @Tobor 's reply here:

The glue strength rule is valid but, it is also conditional. The condition is that the glue must have adequate penetration into all surfaces being joined. Basswood is not nearly as porous as balsa. I know of two good ways to achieve a better bond with basswood using any type of adhesive.
Note: A prerequisite or each of the following is to sand the basswood with as course a grit as the project can tolerate. Another trick that helps is to wipe down the surface(s) with isopropyl alcohol before applying adhesive.

1. Thin a portion of the adhesive to a water like consistency and apply a good coat to all surfaces being bonded together. Immediately recoat surfaces with unthinned adhesive and bond.
2. Use a heat gun or hair dryer to warm the basswood prior to applying glue.

Interesting. I certainly did not do any special preparation of my basswood surfaces, just treated them the same as my balsa. In the future I'll try some of this (even better, I should do some experiments).

Are you using any method to provide pressure between the two pieces, its usually required to get the best glue joints with wood glues.

I usually do apply some pressure, although details vary depending on the situation. In the case of my laminated basswood pieces (two pieces of 1/16" thick stock), I pressed them under books to dry. Those held, but there various places where the lack of bond strength was evident.

I guess the main thing is that in the future I won't just assume I can throw some glue on there and get a good bond. Will have to give it some extra care and see how it goes.

 

[mbeels]

Do you have any close up photos of the separated glue joint?

 

[neil_w]

Just this for the moment:

 

[Nytrunner]

It's also a blessing in disguise.

Better to fix glue joints than broken splintered wood. That's the logic behind the insanity of the superglue crew too

 

[Rocketjunkie]

I've always used Elmer's yellow wood glue and never had a problem with basswood or plywood. Check carefully, the glue may have peeled off a very thin layer of wood.

 

[G_T]

A good glue bond of the class of glue to which TBII belongs has three portions to it.

There is the portion on each side of the joint which consists of glue which penetrated the wood and cured there.

There is a thin layer in the middle consisting of only cured glue.

All three layers are necessary for a good joint. It is easy to do right, but also easy to screw up.

Oil/grease is your enemy. Even finger oils. Clean the wood with one of (Acetone, Denatured Alcohol, high percentage Isopropyl Alcohol). In no cases should one ever use "rubbing alcohol" as this has oils etc added. If hte wood is an oily wood, it will take many passes of cleaning with Acetone to get enough oil out. Expect the color of the wood to change (particularly Paduk).

Allow solvent(s) to evaporate.

Do not touch the surfaces with your hands during or after cleaning. Do not allow solvent to transfer finger oils to the joint!

Wood can be thirsty. Some woods, very thirsty. If one does not allow for that, and just puts a layer of glue between pieces of wood, the wood is likely to wick away the glue and leave a starved joint of little strength.

Take a cup, put some TBII in it, and add a little water to thin it out. Paint that "sizing" glue onto each surface and allow to soak in. If it soaks in, add some more. Continue until it basically stops soaking in. Blot up surface with clean fresh paper towel.

Add fresh coating of full strength TBII. Place parts together, under light pressure. Wipe up what squeezes out.

Light pressure can be a lot of force, if the joint is large. Pressure is force per unit area.

Do not disturb. Allow to cure.

Note, TBII and similar are not gap filling. The joint must be good before applying glue.

Gerald