---

Epoxy and glass notes:

Suppliers:
Epoxy:
Talk to a few suppliers in your area to gain knowledge of the product choice, pricing etc. They will be able to guide you in the choice of resin for your project. My input is to insist on epoxy of the slow cure type with a low viscosity for glass fiber work. The same epoxy resin will be used for sealing the surface of the ply and solid timber, for gluing and for glassfiber work. The slow cure variety will generally cure overnight (depending on temperature) and have a longer pot-life. A long pot-life makes all assembly work more relaxed. Some of the suppliers offer different hardeners that allow you to control the cure time. There are times when a faster mix may be desirable.

Read further in Epoxy application techniques.

Glass:
You will usually find that your Epoxy supplier stocks glass as well as fillers etc.

Glassfiber:
Either woven or stitched glassfiber cloth is suitable for the taping of the seams.

Biaxial stitched cloth has two layers of unidirectional glass strands held together by rows of polyester stitch lines that stand proud of the glass (some users dislike it for that reason, but as the seams need to be sanded in any case I don’t see why). If you use a scraper (or the plane iron out of a hand plane) the next day, while the epoxy is still ‘green’, most of the stitches can be scraped off very quickly.
 
The advantage of stitched cloth, and this by far outweighs the slight inconvenience of the stitching, is that the two layers of glass strands run at 45 deg. across the cloth – in two directions. The joint being taped thus has better strength, especially in shear.
Another benefit is that it conforms better to compound curves such as at the stem.
Weight of glass should be in the order of 400-450g/m2 (12oz). A single tape - inside and out - of this weight is all that is needed for dinghies and small boats, but read the building instructions to get the correct spec.

Woven cloth is the alternative, but I would cut the tapes at an angle of about 45 deg. across the cloth. If cut along the length of cloth, the fibers running with the tape direction contribute hardly anything to the strength.
Woven roving must be the same weight as stitched cloth, but this weight can be made up of two layers of tape.
As the length of individual tapes is shorter with this method (about 140% of the cloth width, that is 1.83m / 6' for a 1.37m / 4'6" cloth), overlaps are necessary if a single tape is used. If you use two layers of about 200g/m2 (6oz) you can butt the ends and stagger the second layers joints.

Updated: 02 August 2005
Back to Tips and Hints menu