Sheathing a Hull with Glass and Epoxy

Over the years Ive 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 Im 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. Dont 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. Dont 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

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Epoxy Encapsulation Prefinishing in Montana!

We can go one step further with epoxy encapsulation: paint some parts before they get set up on the strongback. One of our kit builders is demonstrating this nicely in his Beg-Meil build. He lives in Billings, Montana and started the project this past summer. I advised him to layout all the parts from the kit and precoat them with 2-3 coats of epoxy. He took it further and precoated the bulkheads in his chosen interior color for the boat. This will be quite handy for the bulkheads that are trickier to reach.

You can imagine there is a little more work in tighter places if you do not precoat:

When you precoat with epoxy it is important to think about primary and secondary bonding and your timeline. If you precoat with System Three epoxy, you have a nice long 72-hour window where you get a primary (chemical) bond when you glue pieces together. In a small boat, you can probably put parts together in this timeline. However, with a bigger boat, since it will take longer, it is good to mask off areas that you want to keep as bare wood. This way when you glue those parts (e.g., the end-grain of the bulkheads and 3/4" or so along the sides for the fillet) you can get a primary bond. If you choose not to tape, you can rigorously sand the faying surfaces with 80-grit and get a very good bond, but it will be a secondary bond.

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Quality Plywood Epoxy Encapsulation

I am a believer in epoxy encapsulation of wood; I wasnt always. Encapsulation entails coating the wood with multiple coats of epoxy, saturating the wood surface and building up a moisture-barrier. The moisture barrier is key for bilges and underbodies as it keeps water out of a laminate and maintains a more constant wood moisture content in timbers. Wood movement and ingress of water is what often gives wooden boats a bad name: high maintenance. Encapsulating forms a stable base for varnish and paint. We tell customers to expect a 10 year life for their paint. After 10 years of normal use they may need to do a fresh coat. That is as good as any fiberglass boat maintenance.

What convinced us of the merits of epoxy encapsulation was a visit to my friend Stevens house. He has a faering he built with his son that shows the effects of different plywoods and of epoxy coating wood.

You can see three panels in this Faering. The darker plank is Joubert Sapele faced Okoume (varnished), the middle strake is Okoume by Joubert, and the lower plank in the photo is Shelman Okoume. All planks are finished with a Behr spar varnish.

This is the same boat closer up to one of the tanktops. It is Joubert Okoume. The neighboring plank is Shelman Okoume. Both were varnished the same. The tank top is more degraded and molded than the plank. The tank top along the edge of the plank is perfectly clear. This strip was inadvertently epoxy coated when the squeeze out from the glue joint was spread during the clean up process. The same thing happened in the next photo: can you see where the epoxy is?

The results? It is clear that the epoxy coated areas of plywood are making the plywood much more durable and holding up much, much better. The sheer strake is probably holding up better because it is higher in the boat and receives less foot traffic and a lower angle of sunlight upon it. The middle strake and tank tops get more direct sunlight. But the different brands of plywood may have to do with the difference between planks made of Joubert vs Shelman. It is too bad Shelman went out of business. Clearly, Sapele holds up great and Steven made a good decision putting it in as the garboard. With that said, I have also seen Sapele planked boats flake and shed paint after many years and these were boats that were not epoxy coats.

The moral of the story: epoxy encapsulation is a good thing.

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Covering Star45 model hull with fiberglass and epoxy resin

From: "John Fisher" racer577 at citystar.com
I have used the 3.2 oz satin weave on 7 boats now. The first was a single layer and now that hull is 4 or 5 years olds it is showing wear and tear. I went to using 2 layers to help with durability and to have more material for sanding. Another thing I like about the cloth is that is drapes very nicely and easily will cover the hull with one pc. On my 10Rs I have used 2 yards folded in half to do the hull. On the star I was concerned that it would be too wide for a single yard. I ended up with more than enough material so I cut it on the diagonal.

The glassing starts by laying the glass over the hull. Then I smooth it out so there are no wrinkles. This may take a couple of min. Then I repeat with the next layer. Once the glass is smooth, time for epoxy. I used the 209/105 west systems combination. I used about 10 pumps of material.

I start applying resin to the middle of the bottom with a cheap paint brush. Then I work my way out to the edges of the bottom. Next I do the sides. You need to use lots of resin and dont pull too much or you will pucker the cloth. Once everything is wetted out I go back with a squigee and remove the excess resin. Dont get to carried away or the cloth will go dry again. If in doubt of how this should look practice on a spare block of wood first to get a feel for how the cloth looks as you take out resin.

I did the glassing at about 8 pm and with the 105/209 the resin is still green at 7 am the next morning. When green the glass can be trimmed with a #11 blade in a hobby knife. Then wait another day or two until sanding for full cure. I dont like to do much sanding, instead I try and do most of my fairing by using a thick primer and sanding most of it off between coats. For a clear boat I use polyurethane for a top coat.

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The Easy Way to Remove Cured Epoxy

A frequent complaint I hear from amateur boatbuilders is the dificulty they experience removing excess cured epoxy from glued joints, glass cloth, and fillets. Most people seem to attack the epoxy with a power sander or a chisel, but not only does that make an unpleasant job time-consuming - it also generally results in damage to the surrounding timber.

The use of masking tape alongside glue joints goes a long way towards keeping the job clean, but it is inevitable that clean-up of cured epoxy will have to be done frequently. I have attached a short video clip explaining the use of a heatgun and scraper for epoxy removal, but always try to be as neat as possible in the first place. When using a heatgun, be careful to use the heat to the minimum extent necessary to remove the material, and keep the gun moving so that you dont get deep penetration of heat into the joint.

Here is the video we made in the workshop - I hope it helps.

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