COATING WITH POLYESTER RESIN

SET UP

You can get polyester lay-up resin at Sears, Home Depot, or some auto-supply stores. The catalyst needed is MEK peroxide and is usually provided with the resin.

Check that the resin you’re using is not ‘finishing resin’ or resin containing wax The words you should look for/ use are ‘lay-up’ resin.

Several words on the difference between the two types of resin

Normal lay-up polyester resin is 'air-inhibited'. What this means is that the surface molecular layer does not cure - it stays sticky.

Like a lot of things in the world, this is both good news and bad news.

The good news is that you can build up as many layers as need in a structure. Just keep adding layers. The new layer 'sticks' to the underlying ones. The bad news is that this property includes gel-coated surfaces. Anything will stick to this un-modified surface, including lots of dirt and your socks.

So how do we handle that? Some smart technologist years ago found that if wax were added to the gel coat, the wax shuts off the air contact, letting the resin cure tack-free.

Once more, a good-news, bad-news story. Good news, nothing will stick to the surface. Your socks are safe. Bad news - nothing will stick to the surface. Paint just flakes off.

For application, you will need one or more thin fiber rollers, a roller handle, a roller tray (we use throw-away paint trays), and one or more inexpensive nylon or bristle brushes. Additionally, you'll need several 8 oz plastic or paper throw-away cups and several tongue depressors or paint paddles for mixing.

For personal safety and ease of working, you'll want either latex or some other thin gloves. Acetone or lacquer thinner and paper towels are used for clean up.

PROCESSING VARIABLES

The processing variables for polyester resin are temperature, catalyst level, and time.

temperature - the ideal temperature is around 70°. Never work in direct sunlight, as it provides way too much thermal energy. Don’t work below 65°, as the resin won’t cure. The warmer it is, the faster the resin will cure.
catalyst - for most small repair jobs, 1 to 1 1/2 % by volume is a good starting point. For small quantities, small changes in amount of catalyst can be a big change in percent of catalyst.
time - normal working time, depending on the brand of resin and its age, is approximately 1/2 hour for 1% catalyst at 70°

TESTING

Before you start working on your critical project, run some tests to determine how to mix the your resin, how long it will take to gel, and whether it changes color as it cures (a color indicator is added to some resins which changes as the cure progresses).

Resin after catalyzation will turn from a liquid to a 'jello' consistency (it has gelled). Once it gels, it won't wet out or penetrate fiberglass fabrics; you therefore need to complete the task at hand before it gels.

Test your resin by mixing a small amount with the recommended amount of catalyst. Apply it to a non-porous surface and spread it out. Keep track of the time, and watch for color changes, periodically touching it with a finger so you can feel the differences in consistency. When it has cured (the next 'stage' after gelling), it will be hard but sticky.

Assuming you're using mat (non-woven fiberglass fabric) as part of your project, you'll want to look at handling this fabric. Mat is held together by a binder (glue) to allow storage, cutting, positioning. This binder is dissolved by polyester resin. what this means is that time is important when handling; as the mat can literally fall apart when handled. (Not to get too concerned - 2 to 3 minutes usually is not a problem in handling small pieces).

CAUTIONS: MEK PEROXIDE CATALYST IS EXTREMELY DESTRUCTIVE TO EYE TISSUE. WEAR SAFETY GLASSES OR GOGGLES. HAVE SOME WATER NEARBY IN CASE AN EYE RINSE IS NEEDED.

ACETONE AND POLYESTER RESIN ARE VOLATILE AND FLAMMABLE. DO NOT USE NEAR FIRE OR OPEN FLAME.