There are hundreds of epoxy resins, curing agents, and diluents available. Producers of boatbuilding epoxies are formulators who purchase the resins, curing agents and diluents and mix them to achieve particular design goals. This is a very complex process, because several pairs of design goals are mutually exclusive. For instance, higher quality materials cost more than others, and will drive a higher price point. Dow, Shell and CIBA-Geigy manufacture 90% of the raw materials used by formulators; they all have formulation guides that explain how this process works, and will send one to you at your request.

From a chemical standpoint, each resin has an epoxide equivalent weight (EEW), or number of reactive crosslinking sites on its molecule. The curing agent chosen must be adjusted so that it has the same EEW as the resin. These numbers never match by accident, and so both the resin and the curing agent must be adjusted by adding diluents so that dummies like us can measure it accurately.

So, to take your questions in order:

: This is what I assume to be true about epoxy based upon internet research: 1)
: The 2:1 ratio epoxy may be watered down (solvents added) to increase
: penetration.

Any epoxy or curing agent may be "watered down" with any number of solvents or diluents for any number of reasons. Common boatbuilding epoxies are all 100% solids, that means they contain no evaporative solvents. They may contain diluents to reduce viscosity, reduce price, increase toughness, decrease blush, increase flexibility, produce a clearer color, or any number of other design goals. There is no correlation between ratio and penetrability.

: 2) The 2:1 epoxy tends to have less blush problems.

Blush tends to be a function of additives used in cold weather formulations. The gel time of epoxy goes up as temperature goes down. Most formulators produce one or more products that gel quickly so as to cure faster in cold conditions. These additives tend to make the film react with moisture in the air and create blush. There is no correlation between ratio and blush.

: 3) The 5:1 epoxy has more strength, but may be more brittle.

There is some variation between formulators among strength and brittleness, but it is not so great as you might think. There is a far greater variation in physical characteristics brought about by mixing the wrong ratios. A variation of just 5% can be significant. If the mix is resin-rich, it will be weak and flexible. If the mix is curing agent-rich, it will be weak and brittle. Again, the ratio depends on the original choice of raw materials, not on the ratio.

A minor mistake in volume with a 5:1 product will have a greater negative impact than the same volumetric mistake with a 2:1 product, but off either way produces less strength.

: 4) The Cost of 2:1 epoxy is somewhat cheaper because of the hardner
: additives.

Maybe yes, maybe no. Look on the MSDS for nonyl phenol or butyl acetate. High percentages of these tend to indicate cheap diluents, but again the ratio does not correlate to price.

: I was recommended by an epoxy distributor in Florida to use the 2:1 epoxy
: ratio because the higher ratio epoxies are too brittle. This company has a
: range of epoxy mix ratios starting from 1:1 all the way up to 5:1.

: If I could get some help with the following questions, I would greatly
: appreciate it. I might note that I would probably put up with some amine
: blush if it meant a more structurally sound kayak.

: 1) Are my assumptions listed above correct? If not, what is not accurate and
: why?

See above

: 2) Does the higher strength (5:1) epoxy (if true) translate into a more rigid
: finished boat?

No, that characteristic is governed by the choice and thickness of glass. The epoxy does two things. It constitutes the matrix which transfers forces to the glass, and it keeps water out of the wood. The difference in rigidity of the finished boat is nearly unaffected by the choice of epoxy.

: 3) Is brittleness a problem, specifically with the 5:1 epoxy?

A brittle epoxy may be more prone to crazing and bruises caused from impact damage. But consider that the core of the composite is soft cedar, and realize that dings will happen. The cedar will compress far enough that the glass will stretch within the epoxy matrix and debond internally, causing whitish bruises visible through the finish.

: 4) Has anyone used epoxy from Fiberglass Coatings Inc? If so, let me know
: what epoxy ratio you used and what type of success or failure you had with
: their product.

Not familiar with that one.

: 5) Overall, in general, which epoxy ratio is easier to apply?

2:1 is always more forgiving of metering mistakes.

: 6) Any other insight?

Any of the commonly available boatbuilding epoxies will produce a strong, beautiful and reliable craft. Professional builders seem to stick with West, System 3 or MAS, while many amateurs like RAKA.

: Any help would be greatly appreciated!!!!

We have a tossup here. Pick one and go with it. Enjoy!