by Bob Smith Industries
If CA’s are the cure-all for just about all bonding problems, you may be wondering, “Why do I need epoxy?” One primary reason is price. Epoxy costs are about one fourth that of CA. When large objects are being bonded, economics can be a deciding factor on choice of adhesive. The specific characteristics of epoxies also give them advantages in some applications.
All our epoxies are mixed with a 50-50 ratio. Any scrap material or paper scratch pad can be used as a mixing surface. We have found; however, that the plastic tops to coffee cans work best due to their outer border and their flexibility, which allows the unused cured epoxy to be released and thrown away. Squeeze out equal length beads of the desired amount of epoxy, then mix together thoroughly with a popsicle stick or scrap piece of material.
In cold weather, epoxy takes longer to cure (too cold and usually they never fully cure) and becomes more difficult to get out of the bottle, especially if it’s less than ½ full. The epoxies can be heated in a microwave oven for about 10 seconds so that they flow easier. The heating process, with the caps off, also releases any moisture that can be absorbed by epoxies. Their shelf life; therefore is virtually unlimited.
Acetone works as the best solvent for cleaning epoxy from brushes and unwanted surfaces before it cures. If epoxy gets on surfaces that acetone will attack, use isopropyl alcohol. Isopropyl alcohol that is 90-99% pure can be used to thin epoxy, but by no more than 15-20%. Most rubbing alcohols are only 70% pure. Heat will also cause epoxy to be less viscous. FINISH-CURE is thin enough to be brushed.
Epoxies bond best to clean, textured surfaces. Smooth, non-porous surfaces should be roughened with coarse sandpaper to improve adhesion. A small amount of CA can be used in strategic locations to hold parts in place while the epoxies cure. The minute designations for epoxies refer to the working time, i.e., the time one has before the epoxies begin to set up after being mixed in a large mass. When spread into thinner layers, the working time is increased significantly (Except for QUIK-CURE). Working time decreases approximately 25% at temperatures above 90 degrees F.
Don’t panic if your skin comes in contact with either epoxy or CA. While contact should be avoided, uncured epoxy can be washed from your skin with soap and water. Allergic reactions are rare. Cured epoxy and CA can be peeled off the skin and usually are gone after a full day of normal activity. UN-CURE will debond any body parts that get stuck together if a peeling action (never pulling) doesn’t part them.
QUIK-CURE 5 min. epoxy cures to a slightly flexible consistency. This lack of brittleness allows it to form a lasting bond in areas subjected to high vibration or stress. QUIK-CURE shouldn’t be used in areas that are subject to long-term immersion in water; however, it works fine for the internal structure of wood framed boats. QUIK-CURE is our only epoxy on which you can apply polyester resins. It can be mixed with microballons to form a quick setting putty. Items bonded with QUIK-CURE can be handled after 15 minutes. Full strength is reached in 1 hour.
MID-CURE 15 min. epoxy is used in larger areas where more working time is needed. It is more water resistant and can be used as a substitute for QUIK-CURE in most applications. MID-CURE is our most flexible epoxy and is ideal for gluing to fiberglass surfaces. Allow 45 minutes before handling parts and 2 hours for full strength.
SLOW-CURE 30 min. epoxy works best for forming reinforcing fillets on joints. It has the highest strength of our epoxies. It is waterproof and more heat resistant. SLOW-CURE can be used for bonding if you’re willing to wait overnight. Fillers such as microballoons can be mixed with SLOW-CURE and FINISH-CURE to form a putty-like consistency. Such fillers will usually decrease the working time by about 25%. Bonded objects can be handled after 8 hours and cured epoxy reaches full strength within 24 hours.
EX-SLOW-CURE 2 hr. works as an excellent coating epoxy. It is thinner than the other epoxies and spreads out into smooth layers much easier. It will cure to a clear, hard finish that shouldn’t be sanded. It works well for creating lakes in model R.R. landscapes and for decoupage. You should allow 24 hours before handling. Don’t cure in temperatures below 70 degrees F.
FINISH-CURE 20 min. epoxy is an excellent, low odor substitute for polyester resins. It can be used for applying fiberglass cloth to wood or by itself to give wood a surface ready for primer and paint. FINISH-CURE can be sanded the easiest of all our epoxies and is excellent for the sheeting of foam core wings. Allow 8 hours for full curing. For best results, FINISH-CURE should be heated to a temperature above 85 degrees. For applying lightweight fiberglass, lay cloth on balsa first, then brush on FINISH-CURE. When fully saturated, go over the surface with a heat gun, and the squeegee off excess epoxy with a playing card from an old deck. Heat and remove excess several times for a light weight finish. If room temperature is below 70 degrees use a heat gun on the surface several times for the next 2 hours. When dry, use 180 grit sandpaper on a hard backed sanding block to achieve a smooth finish ready for primer. A second coat of FINISH-CURE isn’t usually necessary. For heavy weight fiberglass, apply the epoxy before and after laying down the cloth. FINISH-CURE is best mixed in a disposable cup in quantities of 1 oz. or less.
Reprinted by permission of Bob Smith Industries 8060 Morro Road, Atascadero CA 93422 All Rights Reserved.
FINISH-CURE, QUIK-CURE, MID-CURE, EX-SLOW-CURE, SLOW-CURE, and UN-CURE are registered trademarks of Bob Smith Industries incorporated.