Cyanoacrylate adhesive

How does this glue work for gap filling? (From WOODWEB's Finishing Forum) March 23, 2003

Has anyone had experience with cyanoacrylate adhesives for gap filling? I want to know if I can use this type of adhesive to glue small sections of various timbers about 4mm thick to a timber substrate. I need quick and very permanent adhesion without subsequent movement, as the pieces are fitted tightly together forming a geometric pattern.

Forum Responses
From WOODWEB's Finishing Forum
CA could work well for this application providing you don't need a high degree of water resistance and the pieces won't be subjected to considerable shock.

Jeff Pitcher

From contributor K:
There are three things to be aware of when using CA.

1. Moisture: If your wood is dry, make sure that humidity is high. Often a heavy breath on the material just before gluing is sufficient. This moisture allows the adhesive to cure properly and will keep it from absorbing water later. It will then be quite waterproof.

2. Acid: Most woods and your skin oils are slightly acidic. CA cures best in an alkaline environment. Dusting the area with baking soda will solve this situation.

3. A tight joint: CA cures when it reaches a certain thinness, in the absence of oxygen. Open cell woods can give you a little trouble if you do not seal the pores first.

With these things in mind, CA can be the best wood glue that you have ever used.

I know that most containers of Jell CA say not to flood the surface. This is because they want to see an "instant" bond. If you flood (cover) the surface then clamp strongly, the CA will act as a hydraulic jack, lowering the pieces together slowly and evenly. Allow 20 minutes to cure before routing or turning. The bond will reach full strength in 24 hours.

Gap fill ability is directly related to the viscosity of the adhesive. Low viscosity adhesives have small gap filling capabilities; they also cure quickly. High viscosity adhesives have greater gap filling abilities and have longer curing times.

A CA adhesive intended for wood is usually formulated to eliminate the acidity problem. Avoid a CA not intended for wood.

There is enough moisture, even in dry wood (about 24 gallons per MBF), that moisture for curing is not an issue. Moisture can be helpful with gluing other materials.

Gene Wengert

Where does one get a good industrial selection of CA glues?

From contributor K:
A simple search on the internet will find many. Depending on your needs this may not be the way to go. Hot Stuff available from Rockler is an excellent craft quality.

Those companies that serve industry often charge more, not less, because of the selective adjustments that they make to the formulas and they avoid packaging for the public.

Getting large containers is not necessarily cheaper. You have shelf life and contamination problems. I find that small disposable applicator bottles are the way to go. Since a .7 ounce bottle can do up to 40 feet of seam (in 1/2" Corian) it is time to dispose of the bottle by that time.

We sell only one "industrial" version, because it is hard to get a good wicking version and the quality was far superior to others we tested. For applications where wicking is not an advantage, I recommend "Hot Stuff" and other brands that are available everywhere.

These types of adhesives, cyanoacrylates, work exceptionally well in tensile applications. This is where two pieces are being pulled apart. Never use in a shear application as they have no strength and will fail quickly. An experiment you can try is to glue two fingers together. Try to pull them apart and you're in trouble, but slide them from side to side and the bond will fail almost immediately.