If too little resin exists, places where the reinforcement is dry will cause weak spots. To optimize the resin content, the entire reinforcement must be saturated with resin with as little excess as possible. An autoclave can elevate the pressure on a laminate two to three atmospheres. While this can be quite desirable, an autoclave is expensive and not readily available to the general public. This brochure assumes that a room cure, hand laminate is being improved and that an autoclave is not available.
Vacuum bagging adds one atmosphere of pressure to a system.
Although the technique is relatively inexpensive and easy to perform, it is worthwhile to understand the principle of atmospheric pressure and how it is measured so that you know if you have a problem with your system. The atmosphere that surrounds the earth can be considered a reservoir of low pressure air. This low pressure air has weight which exerts a force that varies with temperature, humidity, and altitude. When the vacuum bag is first sealed, air pressure on the both sides of the barrier equals that of atmospheric pressure. A pressure differential develops between the closed system within the bag and the open atmosphere.