Does anyone have any proof that a seal coat adds any weight at all or that it adds enough to actually measure?

Surely the timber will absorb roughly the same amount of resin regardless of whether it absorbs it as a seal coat or while wetting out the glass.

Yes, you are right about the amount of resin the wood will absorb. If a thin coat of epoxy is evenly applied, the wood will absorb it differently, depending on the orientation of the grain, and there will be areas which will be slightly glossy and areas which will have a matt, or dry look.

Trying to apply resin to the dry spots, adds extra unneeded weight. I believe using a seal coat will reduce weight IF one fairly light (not runny) consistent and even coat of resin is applied and then the glass is wet-out separately.

Unless the home builder has the right resin thickness, shop temperature, and knows how long to let the wood and glass absorb resin, before removing the excess with a squeegee, the likelihood is the resin will thicken in the glass to a point where it will not be removed with a squeegee, with a dry wood/dry glass wet-out. Resin gets thicker every moment after hardener is mixed in. This adds up to more weight.

I have always strived to reduce weight.

One of the WoodenBoat shows around the year 2000 was held in Michigan, hosted by Gougeon Brothers of West Epoxy. I talked with Jan Gougeon about glassing and he told me they had done research and found if two layers of glass were wet-out at the same time, the glass held more resin, than two single layers of glass wet-out separately. I believe the same is true of wetting out wood and glass together, verses separately.

I believe I'm the guy who started "seal coat" use. Years ago, I and many other builders, had problems achieving a truly transparent glass lay-up. Seemingly good lay-ups would reveal a "silver fleck" appearance when the sunlight hit the boat at certain angles. This suggested to me, all the glass fibers were not totally wet-out. I vividly remember a WoodenBoat show where Nick and I were looking at someone's stripper canoe and asking, "I wonder what causes that silvery look to the glass?"

Not a big issue for most home builders. A reasonable amount of reading resin instructions and luck will produce adequate results for the one boat, home builder, but not good enough for me.

There are a great many variables involved in glassing. Resin brand, resin hardener speed, resin batch size, application speed, amount and method, temperature, glass weave, and most of all, builder experience.

So, I thought about the issues involved and decided to separate the struggle between the wood and fiberglass to absorb resin at the same time.

Until recently, I have only used System Three general purpose resin and hardeners which allow new coats with chemical bonding up to 72 hours. This allows a very relaxed time table for seal coat, glass wet-out, and fill coats. Recently, I've used other resins, which have pluses, but not the long chemical bonding window.

The bottom line for me is the ability to consistently reproduce a totally transparent wet-out. Maybe I'm a worry wort, but the consistent results greatly reduce my stress at giving my customers the best.

Having said that, I don't ALWAYS do a seal coat on my hulls.

Sometimes, on hulls, I will follow all my steps and methods except use a seal coat, IF I have a deadline for a customer, or IF I'm building a boat for myself.

Sometimes, doing only a seal coat, is just more convenient when it's late and I'm tired and I just don't feel like staying up until 2 am. (I can just imagine Etienne working) to do the full glass wet-out, and squeegee excess resin removal routine.

I do ALWAYS do a sealcoat on decks, which are most visible.

For builders using my plans I recommend a seal coat to just reduce the variables, complexity and stress of the all or nothing bare wood, dry glass wet-out. Using a seal coat adds flexibility, slows down the process and eliminates the struggle between glass and wood to absorb enough resin. Wood and glass absorb resin at different rates, with brands, hardeners and temperatures adding to the variables.

I'm a thorough guy. To work as a professional I need consistent results, with economy of labor. After building more than 6 dozen boats, I think I have a good idea of where to focus my attention, what works and what is a waste of time, for me.

For details see- http://www.laughingloon.com/epoxy.html

Your results may vary!

All the best,
rob