Generate Some Heat with Polyester Laminations
Fabricating a polyester lamination can be like a good dinner date. Consider the scenario: you’ve invited a “special someone” over for a nice meal. The house needs to be clean, the room temperature comfortable. The table must be set with all the right implements. And what you bring to the table must be well selected: top quality choices, of course, and foods that work together. Throw in some great conversation and, at the end of the night, you’re likely to get a goodnight kiss. A desirable outcome. The lesson is this: with solid preparation, you’ve generated enough heat for some good, old-fashioned chemistry to kick in.
Creating a polyester composite works in much the same way, and experienced fabricators will confirm that generating heat makes all the difference for parts. This is particularly the case when it comes to working with polyester resins in an open-air environment, if you’re repairing a boat in the garage, for example, or making parts out-of-doors. While polyester resins are generally easy to work with, they must be sealed from the air in order to cure properly. Otherwise, they’ll stay tacky (and nobody wants that in a composite or a date).
Here’s where chemistry comes into play. Once catalyzed, the resin in each layer of laminate will produce two things: exotherm, or heat; and tack. Heat helps the laminate to cure properly, and tack promotes bonding between layers. The more layers in the lay-up, the more heat is generated, which facilitates cure and, ultimately, eliminates tack altogether.
Keep in mind that outside factors, like your technique and workshop conditions, will have an impact. If your workshop is hot—let’s say you’re working with the windows open in the dry Arizona heat of August—your part will cure more quickly. More heat means faster cure. Cooler temps and higher humidity will slow down the process.
Environmental conditions make an even more significant impact on thinner polyester laminates. Chances are, if your laminate is only a few layers or less, it won’t produce enough heat to cure on its own, and the surface will be tacky. In this case, fabricators need to take additional steps to “seal off” their laminate, keeping the air out and the heat in. Here are some things you can do:
- Add Styrene Wax. When you get to the last layer of resin, add the wax at about 5% to resin before lay-up. The wax, which is paraffin dissolved in styrene, will rise to the surface, sealing out air. Once cured, it must be sanded off, particularly if you plan to add other layers. (At Fibre Glast, Styrene Wax is our part #71.) REMEMBER: WAX SHOULD ONLY BE USED WITH YOUR LAST LAYER OF RESIN.
- Spray on PVA. Polyvinyl alcohol, or PVA, can be sprayed directly onto polyester repairs forming a surface film that seals out air for a full cure. When done, it can be easily washed off with water. (PVA is our part #13.)
- Add Duratec Hi-Gloss Additive. If you’re applying gel coat or making a gel coat repair, this resin additive can be mixed 1:1 to accomplish a number of tasks, which includes improving surface gloss, reducing thickness, and permitting a complete open-air cure.
Keep in mind that these methods only apply to thin laminations. If your part only requires a few layers of reinforcement—or if environmental conditions aren’t perfect—take the extra measure to facilitate a full cure. And remember to control the elements when possible: adjust the thermostat, use a dehumidifier or heat lamp, if necessary, and although you want to ensure proper ventilation for safe working conditions, shutting a drafty door or window might help.
If you’ve tried one of these methods, let us know what you recommend—or don’t recommend. Be a part of the composites conversation.