ghost paddler

Curious about Wooden Canoes
was reading a filler post that says silica is glass beads.does anyone know if the media for glassbeading machines is the same or will work??? thanks. mike
Silex is finely ground silica. It uses includes pigments in paint and it is often added to clays for pottery. Silex is not glass micro balloons. Glass micro balloons are also very small and are used in many different things including light weight spackle. Some people are also replacing silex with micro balloons in their filler recipes as the micro balloons weigh less. Some also think that micro balloons hold water. Neither silex nor glass micro balloons absorb water. Ruptured glass micro balloons will not trap any more water in the canvas than does silex. Both are almost pure silica, the difference is the shape. Silex being crushed and ground into random shapes while micro balloons are sealed ultra tiny sherical shapes. Both appear as powders.
You can also get phenolic microballoons that are 10 to 15% lighter than the glass balloons. I do not know if any one has used the phenolic in canvas filler. It is used al lot in filling foam board and fiberglass and used in making surfboards. May be something to look into or maybe some out there can share their experiences phenolic or glass micro balloons
Silica chemistry

I am a retired R&D Chemist. Although my area of specialty was not silica chemistry, I worked for almost 10 years for PPG Industries, one of the major manufacurers of silicas, and used to do analyses of silica research materials. Here are the basics of silica chemistry.
Silicas are not pure elemental silicon (Si). They are polymeric forms of silicon dioxide (SiO2). They are mostly obtained commercially from sands, quartz, and diatoms and are manufactured through two major types of processes; precipitation from silicate solution, and high temperature vaporization/sublimation of sand heated in a furnace. By controlling the conditions of the manufacturing processes the properties of the final product can be highly engineered to yield a wide variety of very different forms, from glasses, to the microballoons mentioned, to coils, and the most common spongelike random shapes. Silicas are not usually crushed or ground to achieve a very small particle size, but instead the particle is created directly in the manufacuring process itself. Crushing or grinding would ruin a very important property of the silica, it's surface area. Think of a ping-pong ball and a spongy "nerf" ball of the same size. The nerf ball has about twice the surface area of the ping-pong ball because of all those nooks and crannys. The surface area is also one of the properties controlled by the manufacturing process because it gives rise to something called surface activity.
The surface of a silica particle can interact chemically with most materials that undergo a phenomenon known as hydrogen bonding. Water is probably the most well known of these materials. Hydrogen bonding is what gives water it's surface tension, solvent properties, and also partly why it is one of the few materials that becomes less dense when it freezes. Many silicas will readily grab onto water molecules and hold onto them very tightly. Heating the silica in an oven will force the silicas to release the bound water. Not all silicas absorb water though. It depends on the geometry of the silicon dioxide polymer.
The oxygen atoms in the silicon dioxide polymer can also react in other ways with materials forming true covalent bonds. Many of the silicas manufactured by PPG were used in formulating synthetic rubber for tires, shoe soles, belts, etc. Adding silica to these materials helped to bond them together during the vucanization process and made them much tougher.
I don't know a lot about the chemistry of the filler materials used in canoe construction. It seems most akin to paint technology. To get the silica to chemically interact with the other components in the mixture you would probably want it to have as little surface absorbed water as possible. Dry your silica in an oven at around 300'F and then seal it up immediately in a glass jar or metal can with as little airspace above it as possible. Don't use plastic bags as they are porous to air over time. Try to use silicas from different sources, precipitated silicas are generally larger particle size with lower surface area, while fumed silicas are smaller particles with very high surface area.
I don't know if this helps, but perhaps it will help you to understand some of the variables better.
John S.