Finishes are put on glass fabrics to allow a strong bond between the resin and the glass. If you take a sheet of glass and put resin on it, let it cure then try to peel it off it will easily come off, or chip off. Finishes like Volan or Silane act as intermediaries between the resin and the glass. Volan has been around a lot longer than the Silanes but I think is still one of the best finishes. Volan is generally the softest finish with the exception of some Silanes. Volan is a chrome based finish that complexes with the silicon dioxide in the glass and leaves one group to bond to the resin. Silane is a molecule that, like carbon, has four groups (bonds) with three of them bonding to the silicon dioxide in the glass leaving one group to bond to the resin. Some of the reasons for using Silanes instead of Volan are 1 - doesn't leave a green tint like Volan which is preferable for surf boards. 2 - forms a little stronger bond and generally considered more moisture resistant. 3 - better for the environment.

When cloth is woven it has an oily starch type material on it to make the glass yarn slide a little easier to prevent breakage. After weaving is complete the cloth is heat cleaned to remove any of this material then the finish is added. There's a lot to know about Finishes and you want to be sure you're getting cloth that is proper for the resin and application you're doing.

The thread count and weave of the fabric can make a lot of difference in the the handling of the cloth as well. Some weaves are tighter than others and are not suitable for complex curves. The satin weaves will take complex curves better but are a little tougher getting the bubbles out. Satin weaves are also effected by the type of finish. This is probably because the yarn is closer together and allows cross bonding of the finish more than in plain weaves. For example, there's a tremendous difference in the way a satin weave like 7781 will be if it's finish in Volan or in a Silane. Some Silanes are pretty good while some can be pretty stiff and good for flat panels only. We sell the stiffer material for a good bit less than the softer material. Unidirectional fabrics are for composites where you need the strength in one direction like in a wing. Or, you need it to conform in one direction more as would be the case for composites tubes. Some of the unidirectional fiberglass styles include 1557, 1543, 3743, 7715, 7721 and 2515.

Silane - is a type of finish on fiberglass cloth based on silicone. It has four bonds like carbon. Three of the bonds are methoxy groups. When they are reacted with silicone dioxide, in the glass of the glass fibers, they give up an alcohol group forming silicone-oxygen-silicone bonds. The remaining bond of the original four is an organic compound that is compatible with a variety of different types of epoxy, polyester, phenolic, and other thermo-set resins. There are many different finish numbers for basically similar types of Silanes. Most Silanes are suitable for epoxy resins. There are exceptions, for example CS-316 is a Silane that is for polyester.

Volan - is the chrome based finish that's been around for years. It is good for any resin. Cloth finished in Volan is generally softer than cloth finished in Silanes. Fiberglass cloth that's finished in Volan may be written as "Volan" on the box or as 504 (BGF), F3, F16, F43 and other numbers if made by Hexcel. The differences may be % concentration of the chrome itself.

Greige - This is in the loom state and has no finish per se except that it still has the oily PVA on it that was on the yarn so the yarn would slip preventing fiber breakage during weaving. Many rubber coaters use fiberglass in the greige for their coating applications.

Other info on Fiberglass

You can get some idea by the count - threads per inch. Warp is length wise down the cloth and fill is side to side. If you laid a ruler on the cloth and counted the threads in one inch that's the number you'd get.

The lighter weight fabrics like 104, 106, 107, 1080, 2112, 2113, 2313 are the ones that have been used in model planes for years, with 106 being the most common to use with epoxy over balsa skins. For molding R/C fuselages softer materials like 1522 3.7 oz, 7533 6 oz type materials are easier to use than tighter weaves.

A lot of the fabrics were first used primarily in the circuit board industry and because of this more is available at cheaper prices. Some materials that are easier to laminate are more expensive because of the higher demand and lower production.

S-2 glass - S glass (primarily S-2 glass) is generally considered to be about 20% stronger than e-glass. S-Glass is 64-66% Silicone Dioxide compare to E-Glass at 52-56%. S-Glass has no Calcium Oxide where E-glass has 16-25%. S-Glass has more Aluminum Oxide at 24-26% where E-Glass is 12-16%. S-Glass has no Boron where E-glass is 5-10%. S-Glass does have 9-11% Magnesium Oxide where E-glass very little. The price of S-Glass is higher than E-Glass. The reason for this that was given to me some years back is that S-Glass is processed at a higher temperature than E-glass. It burns through the oven liners faster and this replacement cost is the reason for the higher price. Most of the materials on this site are E-glass with the exception of styles like 6533, 6781, and 17645 which are S-2 glass and are noted accordingly.

Some methods for applying resins.

Squeegee - When I do big layups like long 4' wide or wider panels I work fast pouring the resin down the center and to to the sides. I make big long strokes from the center out and longways up and down the panel. I move my whole body and not so much my arm independently. Once I get the cloth wet out out or at least exposed to the resin I then go back and work the resin in the cloth harder getting the ideal fiber to resin ratio desired. Using more than one batch of resin I try to get any area completely wet out before mixing a new batch. In other words I don't leave some of the cloth coated on the top with resin not soaking through. In hot weather the resin could start gelling on the top and make it harder for the fresh batch to soak in. After completely wetting out an area using the squeegie you can do a test by slowly pulling the squeegie and if you still have a wave of resin you need to squeegie a little more.

Brush - Use a brush in certain areas only. Don't use a brush for big layups. I normally only use a brush when I'm stippling. I'm sure there's many experts out there that can describe stippling better than I can but I'm going to do my best. Stippling is a combination of a little bit of brushing to deliver the resin to the right place then jabbing with the bristles to force the resin and cloth in where it's supposed to go followed with some brushing to
smooth everything out. This is done in corners, tight contours, taping, but never on flat layups.

Rollers - I personally don't use rollers a whole lot myself and always thought they were more for chopped strand mat. Since I don't use chopped strand mat in anything I don't use rollers. I have used rollers some and they can be useful just not that much for the things I've done.

Resin Infusion - This is where you seal off dry reinforcement using peel ply, an absorbent layer and an outer sealing layer and apply a vacuum which sucks in catalyzed resin from the opposite end of the setup. The idea is to get a vacuum bagged type layup with less work. I have done very little resin infusion and am not the expert in this area.