Epoxy Application Techniques and Procedures
This epoxy manual is relatively brief, and we will try to explain in simple terminology, the more basic procedures of epoxy gluing, coating, and fiberglassing. There are many fine, readily available publications on the market that explain a multitude of advanced techniques using epoxy if this manual does not address your questions. Study the work of at least two authors, for each has his own methods. Some authors may have an affiliation with a certain brand of epoxy, but we can assure you that as a general-purpose marine epoxy, ours is second to none. We base this statement on published manufacturers’ data, our experience, and feedback from the many repeat customers that call us daily.
Please read this manual carefully and always practice proven techniques. Because epoxy has so much strength, the difference between a good and a bad job may not always be easily recognized. If failure happens, it will come at the worst possible time. The epoxy will be blamed when the real problem lies in the user not applying the proper mixing or application procedures. If you have a problem or don’t understand something in this manual, don’t hesitate to give us a call.
Epoxy is not just for boats, but is also excellent for crafts, woodworking, car body repair, and hundreds of other home and industrial uses. With epoxy, even a crude patch-up repair can often be stronger than the original design. Though most of our customers are using epoxy in the construction and repair of boats, it also can be an excellent adhesive and filler that bonds well with metals, concrete, and some plastics. The production of fiberglass boats of today is usually constructed with cheaper polyester-type resin. Polyester resin is used because of its low cost and quicker cure time. Its shorter shelf life is not a problem for large volume users. Epoxy resin and hardener, on the other hand, have an indefinite shelf life, are much stronger, more flexible, and much more waterproof. Epoxy resin products not only have a greater bonding strength but also will bond to a greater number of different materials, including cured polyester resins. It’s for these reasons epoxy is used for so many boat repairs.
We have tried many of the epoxy products that you see in your local marine and hardware stores, from thick pastes to thin penetrating epoxies. I find, for the most part, they are of high quality and do the job for which they were intended. The problem is that they can be quite exorbitant in cost. We have found that for most boat and shop applications you can custom-make your own epoxy products. Take our low viscosity epoxy and mix it with one or more of our fillers, and you can have an epoxy product tailored to your specific needs.
WHAT IS OUR RAKA EPOXY SYSTEM?
We have several different epoxies with a variety of mixing ratios and curing times. We purchase the basic epoxy resins and hardeners in bulk from different manufacturers and then blend them to get a finished Raka Epoxy. One way, Raka Epoxies are different from many industrial epoxies is that we mix in different and expensive additives that help with better flow and air release. Especially in thin coats, you will notice less pin holing and cratering. The products we ship to our customers with our Raka name will be easy to use and give consistent performance. We can offer lower prices because we don’t have distributors and dealers to support, so we are free to sell directly to the customer.
BASIC TECHNICAL INFORMATION
Our main epoxy resin 127 is a low viscosity, thin, liquid. It is basically thick standard-grade resin that has been thinned with special additives and reactive diluents. When mixed with its companion hardeners, it will cure to a very tough waterproof plastic. We have several hardeners with different mix ratios and curing times. Raka mix ratios are by volume and not by weight. Please note that our epoxy resins and hardeners have no evaporating solvents, so you will get no shrinkage compared to polyester resins and some solvent-loaded epoxies. Some people prefer a one-to-one mix ratio because of the simplicity of mixing. Our Table Top System mixes together one part resin to one part hardener. It is designed primarily to be used as a thick coating epoxy for tabletops, bars, and crafts. It is a very clear nonblushing epoxy system. The high viscosity of Table Top also makes it an excellent general-purpose gluing and repairing epoxy. Table Top epoxy tends to be more flexible and has somewhat less strength. Pot life is approximately 40 minutes. The hardener 631 is a medium-fast curing agent that can be mixed at a ratio of five parts resin to one-part hardener. 631 gives the most strength and heat resistance, but you have to give more care to the critical mix ratio and is subject to more blushing. 631 is not recommended for clear coating. Our best-selling hardeners are the 610 which is very fast curing and the 606 which is slow curing.They are mixed at a ratio of two parts resin to one-part hardener. The two-to-one ratio epoxies are probably the most popular because they give a good compromise in ease of use, are low blushing, and have good overall physical properties.
I’ll give a brief description of our two-to-one epoxies because these are what our customers most often request. Depending on the job requirements, you can choose a fast or slow hardener or a combination at no extra cost. At 77 degrees [F.] the pot life (using 3 mixed ounces) of the fast hardener-resin mix is about 8 minutes. Three ounces of slow hardener would give you about 25 minutes of working time. A mixture using only fast hardener 610, can be used down to 50 degrees F, and using only slow hardener 606, should not be used below 60 degrees. A useful feature of the two hardeners is their ability to be blended together to customize a cure time for your particular requirements. We recommend when working under 70 degrees, use a blend of hardeners if you want a working cure within 24 hours. The majority of our customers divide their purchase of hardeners into equal amounts of slow and fast. When epoxy systems are described scientifically, you will hear frequently used terms such as hardness, flexibility, impact strength, resiliency, modulus, etc. These are measurements of physical properties. You must be aware that you can’t have all the best properties in any single epoxy. A good characteristic in one area is likely to give you a poorer showing in some other area. When we selected our Raka system epoxies, the prime considerations were to get good general-purpose boat building and woodworking characteristics. One of the outstanding qualities of our epoxy is that the mixed resin and hardener have a lower viscosity than some other epoxy systems. This allows deeper penetration into the wood and very thorough saturation when wetting out fiberglass cloth. Bubbles that are introduced when mixing dissipate very well to give you a smoother unblemished coating. A thinner mix also allows easier mixing and higher loading of the many fillers that are available. An example would be loading your epoxy with a higher proportion of micro balloons to achieve easier sanding of the cured epoxy.
MIXING
The different Raka epoxy resins and their companion hardeners are engineered to be mixed in a precise way using a certain volume or weight of resin for each volume or weight of hardener. Some of our manufacturer’s specifications give the mixing ratios by weight and some by volume. We feel that mixing by volume is simpler and the mixing instructions on our labels specify using volume measurements. Correct mixing volumes can be obtained by the use of measuring cups or by the use of our pumps. Before starting any project, check the pumps for metering accuracy and also check your measuring cups as many cheap cups and pots have inaccurate marks. In a clean pot, mix thoroughly in a nonbeating motion and not too fast as you will introduce air bubbles. Make sure that the liquid that slops up on the side of your bowl and on your mixing tool gets mixed also. Ideally, you will pour the mixed epoxy from the first pot into another container and mix again for the most consistent mixing of all the hardeners and resin. This may be extreme and too time-consuming for most people but will insure a more consistent mix. If you plan to add any fillers, do so only after completing your initial mixing. Mixed epoxy that is in a mass can heat up and become unworkable very fast. Experienced users work with small batches so there is less waste. It is important to remember that epoxy applied in a layer thicker than 1/8 inch may produce enough heat to damage the substrate or cause the epoxy to foam (especially of concern when using fast hardeners under warm conditions). Immediately after mixing (especially when using the fast hardener), spread the epoxy out on a flat surface in a larger container (a plastic plate works fine). In some cases, if you want a faster setup and cure time, it is better to leave the mixed epoxy in its pot for a few minutes so it will get a chance to heat up. The epoxy curing process depends on the heat from its own reaction and the ambient temperature. You will have to experiment to understand each epoxy’s properties. I want to emphasize the importance of proper mixing. Epoxy’s strength and desirable properties come from the complete mating of the resin and hardener molecules in the correct ratio. Too little hardener produces brittleness, and too much hardener makes your epoxy softer with the accompanying loss of strength.
FILLERS
With the proper selection of fillers and the basic resin-hardener mix, you can create a dozen products that you would pay dearly for in your local marine store. Just five of the more common fillers will be explained here.
(1) Silica: It’s sold under a variety of names and product codes (fumed silica, aerosol, cabosil, etc). For general purpose use, silica is an economical and widely used filler. Though any filler can thicken a liquid, silica has the unique properties of being very smooth spreading, strong, and thixotropic (non-sagging). Thixotropic qualities are especially helpful in allowing your fairing paste to hold its shape, and preventing run-off on vertical and overhead work. According to the amount added, you can achieve a viscosity from thin ketchup to peanut butter. It can be used for gluing, laminating, and making a very smooth fairing compound. Silica is also very useful for making fillets that are useful in structural and cosmetic applications. Fillets are probably most commonly used to fill in sharp corners between two glued pieces. Strength increases because your glued surfaces are spread over a larger area. Silica sands very hard, so smooth it and clean up well before the mixture cures.
(2) Micro balloons: Tiny glass spheres are used to thicken epoxy and make an easily sanded fairing putty. Though not as strong as silica, it is much easier to sand. It’s usually wise to add some silica. It makes your putty easier to spread and helps it hold its shape once applied to your project.
(3) Milled glass fibers: Finely ground glass fibers that are added to epoxy to thicken and add high strength. Adding silica also improves the properties of the mixture.
(4) Chopped Glass Strand: One-quarter-inch chopped course fiberglass strand that makes a very rough filler for exceptional strength and large gap filling.
(5) Wood Flour: Makes a good wood-toned non-sagging putty for fillets and gluing.