When the resin and hardener are mixed together, a heat-producing reaction (called "exotherm") begins. At 70oF no reaction will be noticeable for about 8 to 12 minutes with POXY-SHIELD®-Fast and about 20 to 30 minutes with POXY-SHIELD®-Slow or POXY-GRIP®. These times will vary depending on the quantity mixed and the shape of the mixing container.

During the next step in the cure process, the mixture will start to get warmer and thicken(*), then change to a solid material. When a noticeable warming starts, discontinue working with the mixture. Several hours after application the resin will be relatively tack-free. Sanding can be performed after a nominal overnight cure. While the reaction may seem complete after this period of time passes, a total and complete cure will require several more days. Ultimate physical properties are not reached until this time. Because of the period of time involved in this chemical reaction, bonded joints should not be stressed for at least 24 hours after application at 70oF. At lower temperatures, it will be necessary to allow longer cures.

(*) The period of time when the resin changes from a liquid to a non-flowing gel is called the "gel-time", and is also the amount of time available to work the resin once applied to a surface. The period of time that the resin remains workable in a container until it must be discarded is called the "pot life". In spite of this fine line of definition, the terms are often used interchangeably.

In boatbuilding situations, room temperatures in the 70oF range as described above may not always occur, thereby varying the reaction from that previously described. Warmer temperatures will speed the reaction, while cooler temperatures will slow it down. Thus it may be necessary to control the cure rate of reaction to suit local conditions. In other words, you can speed up the exotherm by the addition of heat, or slow it down by withdrawing heat (making things cooler).

On hot days, extend the working time by placing the resin container in the shade, or even in an ice cooler, refrigerator (free of foodstuffs), etc. Resin in a large concentrated mass will cure faster than resin spread out over a large flat area. So in warmer temperatures, dispense the resin into a large, shallow pan, paint tray, etc., so the heat can be more easily dispersed. Also note that the addition of fillers (particularly fibers) will tend to insulate the resin and speed the exothermic reaction.

In cooler weather, the viscosity of the products may increase dramatically, making measuring and mixing more difficult. Therefore, keep the products in a warm room, and if necessary, set the containers in warm water to bring their temperatures up to 70oF or more to make them more fluid before mixing. The resin and hardeners by themselves should ideally be at about 70oF for best mixing. lf below this, the viscosity increases and mixing is harder. lf above this temperature, pot life will be decreased when mixed. Do not thin the products with solvents or thinners.

For faster curing in cold temperatures, leave the mixture in the mixing container for a few minutes after mixing to help initiate the exothermic reaction before dispensing it into other containers for use. Also, gluing surfaces can be warmed by local application of heat, such as with light bulbs, heat lamps, hot-air guns, etc. However, do not use open flames for this purpose and be careful that any such heat-producing appliance will not cause damage to the structure.

Heat should not be applied to such an extent that cure is achieved too quickly; this can cause a loss of physical properties. Also, under no circumstances should too much heat be applied (as with a hot-air gun) thereby causing the resin to foam; this will cause a severe loss of strength. Finally, DO NOT ATTEMPT TO VARY RESIN/HARDENER RATIOS IN AN ATTEMPT TO VARY CURE TIMES, regardless of ambient temperatures; the mixing proportions are important to achieve a product with all the physical characteristics intended, even though cure may be possible with less-than-perfect mixing proportion.

Return to Contents