Wednesday, July 6, 2011

Sheathing a Hull with Glass and Epoxy

Over the years I've discovered a number of building issues which people find intimidating, and one of those is the process of sheathing a hull with glass cloth and epoxy.

As with most things in small boat construction, glass sheathing is not difficult, but it must be done the correct way if one is to avoid a bad result. It is just as expensive and time consuming to do things the wrong way as it is to do it properly, so some research and preparation is time well spent! There many 'correct' ways to do the job, but I'm going to give you a very brief insight into the method which works for me. Because of space and time limitations, this is just the most basic demonstration. I hope it helps.

Prepare surfaces with longboard and other sanders. Round-over edges
Fill gaps with epoxy and sanding filler
Re-sand all surfaces with 80-grit paper to provide a good "tooth" for the epoxy, and thoruoghly vacuum the dust
Fill any minor blemishes and sand details
Drape hull with glass cloth and cut roughly to size
Tape overlaping areas and edges in place with a few pieces of masking tape
Smooth out cloth with a dry brush held at about 45 degrees to the surface
Trim overhanging edges with shears or scissors
Ready for epoxy
I did one side at a time on this job, so I peeled back one side and held it in place with lead weights
Mix up small batches of epoxy, pour on in sections, and spread with a squeegee held at a shallow angle. Don't press too hard, or the mix will become aerated. Just gently move it over the surface and allow a few minutes for the cloth to wet-out. Don't worry about an even finish yet - just distribute the resin and allow the wetting-out to proceed on its own.
Attend to details such as the dry edges with a disposable brush
Continue working downwards until the whole section is completely wet-out. There is no rush, as long as you continue working out from a wet edge.
When completely wet-out, remove excess resin using a squeegee initially, and then finish off with a dry foam roller. The aim is to remove all liquid resin from the surface, leaving just the wet cloth with no puddles
The result should look like this - an even, textured surface with no pools of liquid resin. The glass cloth should be in direct contact with the timber, and not be 'floating' in puddles anywhere.
Another good example of a proper finish after the initial wetting-out coat.
After the first coat has cured to the point where it has stuck the glass to the surface, but before it has fully cured, a second coat can be rolled or brushed on to fill the weave of the cloth. This is usually followed by a third coat a few hours later. In this photo you can see how the weave of the cloth has disappeared.
Here is the hull at a later stage after the hull has been sanded. Because of the fill coats, and the smooth application process, the sanding was done without cutting into the cloth - just the fill coats of epoxy were sanded.
For bigger jobs, extra hands are required to get things done before the epoxy goes off. On this 22ft hull, we had my wife, the owner/builder, and myself all working in a team
The result speaks for itself


  1. Thanks for sharing these insights into boat building Ross.

    Something I'm having trouble with is getting a consistent taper on a small diameter spar perhaps you could share some gems with us.


  2. Hi Ross, great post. I've been teaching myself to sheath with mixed results, this has been really useful. Phil.

  3. Phil,

    Thank-you very much for the feed-back - it is gratifying to find out that what I've written may be of some use. I really just pull things out of my head and hope the subject matter is of interest - not always an easy thing to do!


    I'll write a short post specifically dealing with your question - nothing earth-shattering, but it will show what works for me.

    Ross Lillistone

  4. That was great! very informative. You have nice technique and the results are impressive.