14' Strip plank canoe sheathing inside

This weekend I decided to epoxy/glass the inside of the canoe. I used the same 200g/m cloth as the outside. I went through the same procedure of tack clothing the surface, getting the humidity and temp right and making sure the resin was room temp. This time I did it on my own and it took a fair while, most of this was dispensing and mixing the resin. The room was fairly airtight and it was starting to smell of curing epoxy pretty strongly towards the end of wetting out of the cloth. Next time I will wear a mask with charcoal filters.
I rolled the cloth out over the boat and cut it to length. Then I dropped it into the hull and tried to smooth it by pulling rather than brushing with my hand. I still got a couple of ripples in the finished item.

This pic shows the weave that is visible after one coat of epoxy. The next 2 coats do hide this to an extent. On previous canoes I have used 145g/m cloth that seems to be less liable to rippling and is less visible.

One thing to check if you have a go at doing this is how much epoxy is gathering in the middle of the hull at the bow and stern. This can mean the epoxy goes cloudy and bubbly as it exotherms. I had to keep mopping up the excess with a brush. Don't be tempted to spread it around to try and get rid of it as you will get a cloudy patch.

 I didn't get too fussy about the glass at the stems as it gets sanded neatly later and will be hidden behind small bulkheads. The bulkheads are just cedar strips glued together on a flat surface. The shape was taken from the hull by using a process called spiling, its a bit like scribing. These also got sheathed at the same time.

Next up is sanding the inside and planning and making the gunwales. I'm going to leave the sanding for a few days to get a full cure.

14' strip plank canoe inside prep'

This week I managed to get time to sand the outside of the hull and scrape and sand the inside. The outside sanded fairly easily thanks to being able to maintain a decent temperature and humidity during the cure. I used a dual action sander, first with 80 grit then 120 grit, both without an interface pad. I was sure to keep the machine moving all the time and used diagonal strokes to try and fair out any anomalies. I wore a protective waxed paper suit, nitrile gloves and a proper face mask to stop the epoxy dust. From what I've read, once you are sensitised to epoxy it seems you just have to stop using it or wear a space suit!

Next came the removal of the moulds. I took out the screws that were holding them to the strongback (building table) and gave them each a twist. Most of them came away easily and I pulled them out from under the hull. The formers for the stems had to be hammered out to free them. I drew around one of the narrow station moulds and made a kind of shoe to hold the canoe at both ends once it was turned right way up. I flipped the canoe with the aid of a helper (this time Mrs Newton Boatworks) and then sighed after seeing the amount of scraping and sanding to do on the inside!

Despite wiping the hull inside with a damp cloth when the glue was still wet, there were hard bands of glue where the station moulds sat. Although the cedar strips interlocked nicely, they are a series of flat surfaces that form a curved shape. This means having to scrape/sand the inner surface to lose the flats. I filed a paint scraper to a decent curve and used that to get rid of the glue bands and fair the shape. This means walking a fine line between skidding over the glue surface and digging into the soft grain and tearing a chunk out.

With this done, I got out the sand paper and sanded the hull 80 grit and 120 grit. It's essential to wear a dust mask or you end up coughing all night. I even shaved off my beard to get a good seal on the mask. I vacuumed the dust/shavings up and then mixed some epoxy/different fillers/sanding dust and flush filled any gaps. I used a high proportion of the hollow glass microspheres as they lower the density of the epoxy mix and mean you are less likely to sand a hollow into the cedar either side of the filler.

I then re-sanded the filled areas and cleaned up ready for sheathing the inside. 

 

14' Strip plank canoe sheathing

In a bid to get the hull finished I checked the humidity and temperature in the workshop to see if I could crack on with the epoxy/glass cloth stage.

 The hygrometer showed 97% and the temperature was just 11 deg C. It's important that the epoxy coating is applied when the humidity is lower (max 85%) and the temperature higher, to avoid an under-cure and a cloudy finish. I didn't want to wait for the weather to improve so I put the dehumidifier in the workshop for a day. This didn't bring the humidity down a great deal as the workshop is pretty draughty. I fitted foam tape to the door seals and a thick polythene sheet to catch any drips of condensation on the underside of the corrugated iron roofing.

The next day I got up at 6 am and set the fan heater up under the hull. The outside temp was 5 degrees. I got the temperature up to 15 degrees and the humidity down to 70%. The resin had been warmed in the house for a couple of days. I read somewhere that you should aim to to get a dew point that is at least 3 degrees lower than the air temperature to stop condensation forming on the epoxy and making it cloudy. The hull has to be the same temp or warmer than the air. I used this dewpoint calculator. Other advice is keep an eye on the temperature whilst doing the sheathing of the canoe as an increase in temp will cause air in the wood or voids to expand forming bubbles under the cloth.

The cloth is 200g/m and a little thicker than I have used before. I used West System resins and the 207 hardener which is intended for this kind of clear coating. It's great to see the first batch of resin poured on and the wood showing through. After I had wet out each quarter of the hull with a brush I went back over it with a filler card to take off the excess and get rid of air bubbles. 

Once this first coat was tacky I brushed on another coat with as few runs as possible. The idea of this is to create a chemical bond between layers. Once this was tacky (8pm) I brushed a on final coat. I left the heater running for 24hrs to keep the temp up and get as good a cure as possible. The ouside temp was only 3 degrees at night. Trying to sand chewy epoxy is bad for your health (skin and respiratory sensitisation) and uses up loads of sanding discs.

The shape of this hull has some tumblehome which meant that the spare skirt of glass cloth was trying to pull the cloth off the hull. I trimmed this as I went and smoothed it back on.
Once the three coats were all on I could get an idea what the completed canoe will look like when varnished.
This is then sanded, the moulds removed and the boat turned over.

I've just got to do the same on the inside!

Hull sheathed and 3 coats of epoxy on: time for a beer

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