Glue
There are a number of different criteria I use to decide on the type of glue to use for different applications and I would like to talk a little bit about that in this blog. Exposure to the elements (inside or outside use), density and oil content, color, stability, and use of end product. Below is a partial list of common glues I have used in the past.
1. Plastic Resin (water and powder mix). This glue is too brittle and I don't recommend using it for any circumstances.
2. Urac (powder and resin mix). A urea-formaldehyde glue. It's very strong, has good gap filling qualities, and is good for exterior use. It comes in second place to Epoxy for oily/dense woods. Wear gloves and mask when mixing. I have replaced it's use with Titebond III which has a very low toxicity level and is just as strong and versatile for interior use.
3. Gorilla Glue (urethane glue) is very strong but because of foaming I don't use it when other glues are as strong and much easier to work with.
4. Resorcinol (powder and resin mix). This leaves a dark glue line, and has all the same good and bad qualities as urac. I use epoxy in its place now because of more versatility.
5. Epoxy (liquid hardener and resin). I mostly use West Systems for exterior use, dense oily woods, and in the vacuum press for bent laminations (epoxy doesn't need air to cure). It is very toxic and care must be taken when using it.
6. Titebond III (yellow or tan, water clean-up) I use Titebond III by Franklin on interior and some protected exterior work. This glue is very strong, gap filling, #1 type water resistant, easy clean up, and low toxicity.
To sum up the above, I use two types of glues now. West Systems Epoxy on exterior heavy-exposure areas or where extra strength water resistance is needed, on dense and oily woods like teak and rosewood, and in vacuum press bent laminations. And Titebond III on interior work.
West Systems requires special pumps for mix ratios. You should apply an even coat of properly mixed hardener/resin, wait 10-15 minutes for it to soak into wood surfaces and then mix another batch of epoxy adding 20-30% by volume of colloidal silica to epoxy mix and again apply an even coat to both surfaces. Apply a light pressure with clamps, 5 to 10 lbs. Any more pressure will drastically reduce joint strength.
Another thing to remember - don't use silicon lube on your machine surfaces, it will contaminate epoxies. Thoroughly mix epoxy. Different hardeners are available to lessen or lengthen open times. I buy West Systems at a local marine supply store. Clean up is with alcohol. Always wear gloves, it's very toxic.
And, as I said before, I use Titebond III mostly on interior work. I don't recommend its use for dense, oily woods. Being water resistant doesn't hurt, especially on bath and kitchen work. It has a longer open time (about 30 minutes at 70 degrees Fahrenheit) which helps for the more complex glue ups. Apply an even coat to both surfaces and not too much pressure or you'll weaken the joint, up to about 15 to 20 lbs. is good. Clean up is with water. Don't forget to wear gloves, even though its a low-toxicity glue. This glue is a good choice where food will come into contact.
I hope I have explained the differences between glues, and you have a better understanding of the applications each type is used for.
