•Knife Grade: Consistency is similar to spackling putty or creamy peanut butter
•Flowing Grade: Consistency of a motor oil
•Penetrating Grade: Consistency of water
•Super Penetrating Grade: Consistency of a solvent such as mineral spirits or paint thinner
Generally knife grades are used for repairs with fills more than 1/16 in. wide. Flowing grades are used for repairs smaller than 1/16 in. and for laminations and rodding.
Penetrating and super penetrating grades are rarely used by fabricators, but can be used to resin stone and on applications where an adhesive is needed to penetrate very small pores.
Today's adhesives are available in a number of colors; however, there may be times when you need to add coloring. Many adhesive manufacturers have tints that you can use, but if you're in a pinch I have found that artist's oil colors work well for most polyesters. Epoxies, however, need tints designed specifically for them.
General Adhesive Properties
Temperature: All adhesives are sensitive to temperature and humidity. This means that cure times will vary. Adhesives will cure faster with increasing temperatures and slower at cooler temperatures. Temperature will also affect the viscosity. Higher temperature will thin the adhesive. There are also several heated dispensers for epoxies that work well for faster cure times and easier flowing.
Cure Time: The general rule of thumb for most adhesives is the slower the cure time, the stronger the bond. An epoxy with a seven-hour cure time is going to be much stronger than an epoxy with a five-minute cure time. If too much hardener is added to polyester, though, you will increase the cure time but reduce the bond strength.
UV Exposure: Nothing is 100 percent UV proof; however, epoxies are more UV-resistant than polyesters and are the adhesive of choice for outdoor exposure.
Moisture: Polyester is very sensitive to moisture and for that reason it should be avoided in wet areas, such as showers. Epoxy has a much higher tolerance for moisture and is the adhesive of choice in wet areas. When using polyester, you must make sure that the stone is completely dry. Epoxies can tolerate some moisture.