Unveiling the esoteric secrets of epoxy resin works. /PART 1

One of the most common fear of newbie boatbuilders involved in our projects is related to the use of epoxy resins and glass fabrics.

Since this is a very important part of our projects to achieve a strong, light and long lasting boat, we will give some tick and trips on the subject; the following tips are mostly based on my experience as a boatbuilder, so they are not the bible, but at least every single tip has been personally tested.

Let us start form our main protagonist : the epoxy resin !

  • learn your resin system: each resin system has pro and cons but the most important thing is to “learn” the behavior of the resin you selected for your build; I am not going to endorse any specific brand here, as long as you stay within renown brands it is fine, the important thing is that you learn how it behaves with the different hardeners (you will use at least a medium one and a slow one for different operations), how viscosity is affected by temperature, how is the real pot life in your working environment , how it reacts when mixed with silica or cab-o-sil powder, and so on.

  • Temperature is a key factor: temperature will affect the pot life of your resin of course, that is to say to say the amount of time your mixed resin will be workable, but this is not the most important fact. The most important fact is that temperature will affect the viscosity of your resin changing from very liquid, almost like water, to a kind of honey like viscosity ; this will affect HEAVILY your capacity of soak glass fibers, a super easy work with liquid resin , a hard and annoying work with honey like resin, that will lead to a poor lamination with an excess of resin and a possibly resin starving glass fabric (this seems a contradiction but it is exactly what happens, you will pour too much resin fighting with high viscosity and you will not be able to soak the glass fabric poperly)
  • how to master temperature ?
    • Cool down or heat up the resin (it is a smart idea to do this operation with all the amount of unmixed resin you will need in the next few hours)
    • mix only the resin you will use in the next half hour of work
    • in case of cold: keep the resin hot not only before mixing it, but also when you are laminating the areas (a small hair dryer is a good help)
    • try to cool down or heat up all the working environment: this is a little bit tricky, but if you can do it, it will solve a good part of the problems
    • avoid the coldest /hottest part of the day and NEVER work under direct sun during summer (unless you do not live in Norway or similar)
    • it is really difficult to use resin with decent results under 13° C / 54° F and above 33° / 92°F
    • avoid days or environments with super high humidity , it is better to avoid resin works with more than 75% of relative humidity , if you are somehow condemned to work with high humidity (on the seaside, for example) try to investigate which resins on the market are less humidity sensitive

  • weight is mandatory : epoxy resin must be mixed in the exact proportion given by producers (we are currently using an epoxy system that has to be mixed 100 grams of A component with 24 g of B component, for example) , this is a very important factor if you want to have a good quality lamination or bonding.
    • Use an electronic scale or volume pump (I prefer by far the first one, cheap and super precise) ; print a datasheet in which you detail the A and B component for the most common quantities (100g—>24 g, 200g—->48g , 300g, 500g, 700g, 1 kg and so on, for example) ; and stick the printed page on the wall near the scale, and CHECK it every single time you pour and mix the resin ; professionals do it, you can do it too;
    • volume mixing ratio vs weight mixing ratio: some epoxy systems give both of them in their datasheets, you need the ratio by weight to use a scale; they are different because A component and hardeners have different density ; in case you need ratio by weight and this is not given on the datasheet remember that weight = volume x density (or ask resin manufacturer the info)
  • mix the resin properly: that is to say for at least one minute with a wooden stick or similar.
  • Thickened resin: we will use it as a bonding compound and to make the so called “liquid joinery” or “filletting“ works (thickened resins radiuses), so it is very important to master the subject.
    • First mix the resin (A and B component) properly, then add the thickening compound :this is mandatory to have e good resin setting
    • resin viscosity matters, here too (temperature matters, again): if you start from a honey like resin the quantity of powder required to achieve the desired final consistence will be affected.
    • Which thickening powder have I to use ? The better solution is that your epoxy producer has in catalog a thickening powder ready to be added to give a strong, light and slightly elastic bonding compound; otherwise I normally use a mix of silica and cellulose fibers (about 50/50) ; sometimes you can find on the market ready to go bonding compound cartridges, they are expensive, but it may be a good choice , it is by far better if they are based on the same epoxy brand you will use for the other works. You can find a good product on the market under the name cab-o-sil (hydrophilic fumed silica powder).
    • PAY ATTENTION: cab-o-sil or similar silica based fillers are toxic to breath and they are super light, a gust of air and they will literally take off
    • resin volume grows A LOT : when you add thickening powder total volume will grow approximately THREE-FOUR TIMES , that is to say 250 grams of mixed resin will result in about one liter of bonding compound !
    • The right density is when thickened resin stop to flow and stays in position even in vertical faces but the compound is still soft and with all the powder perfectly mixed; avoid to add too much powder, the final compound will result grainy and too hard to smear to form good shaped radiuses , once set it will result to brittle and prone to crack under stress

the next episode can be found here

few images, just to complete this starting chapter: the typical resin cans for big projects, two cans of resin and one of hardener , an electronic scale protected with tape and battle ready , cheap and super precise , and a small weather station, quite useful to keep track of temperature and humidity in your working environment , and a pack of wooden tongue depresser, which are cheap and super useful to mix resin and other small tasks