By Bob Pierce, written to Ragwing Online Group:
Asking what is the best type of glue is almost like asking the best brand of beer. Most people have a preference but they all will do the job (with certain limitations) . I have built 7 aircraft several of which were all wood construction and I have used most that have been available.
Let me begin by saying that price should not be a factor. You do not want to nickle yourself on one of the most important items going into your ship……However ease of use is important.
Rescorcinol —– Probably of the first of the glues use in aircraft construction that is completely waterproof. A 2 component glue that requires an accurate and close fit of parts to be glued. The clamping pressure required for a good joint is high and it should be evenly applied for best results. Many have used and liked it. I tried it on my first ship and was not pleased with the results. Poor gap filling properties. Well fitted joints are important.
Urea formaldehyde. — Weldwood Plastic Resin, Panite etc, Usually comes with hardener in the dry powder mix. Mixing with water activates the hardener and prepares the product for use. Formerly very popular. Has adaquate pot life, is easy to mix and use and is highly water resistant. Weakens at high temperatures such as can be found inside the wing of an aircraft parked in strong sunlight. I personally do not consider this an important factor. Available at most hardware stores
Polyurathane. — Gorilla Glue, Excel. 1 etc……Has seen increasing use in recent years. Comes pre mixed and easy to use. Apply glue to one surface and dampen the other. When brought together a chemical action occurs curing the glue. It swells and foams while curing. The glue forced from the joint by this action looks rather messy but other than appearance it is of little importance. What I don’t like is that thin material such as plywood tends to be forced away from the joint by this action possibly leaving a thick glue line. I have used the product with satisfactory results. Hghly resistant to moisture. Available locally.
polyvinyl acetate.….Often called white carpenter’s glue. Sometimes yellow in color. Ready mixed and simple to use. Some types very water resistant. Softens with heat. Joints can creep when subjected to constant high stress. I often use use it in non structural areas such as turtle decks, fairings etc…Requires good joint fit.
Epoxy.….Most suppliers carry a product approved for aircraft use. T88 is very popular. I use it exclusively for all structural work. It is a 2 part mix, usually 50/50. It neither swells or shrinks while curing. Proper mixing is important but relatively simple. Adaquate pot life. Setting time is temperature sensitive and it should be used at near room temperatures. There are types available for low temp. use. Sets up over night. Excellent gap filling properties and a tensile strength exceeding that of wood. Completely waterproof. DO NOT get it on your hands. Rubber gloves a must…..uncle bob