Red Cedar Kayak blotch

[Toymaker Len]

I've made these kayaks from 3mm red cedar ply (stitch and glue, epoxy on 6oz. cloth, linear poly varnish) and after about four months these unsightly blotches have appeared on one of them. I guess it is infiltration of moisture somehow though everything is sealed both sides with epoxy. The question is what to do if any thing? Meanwhile they work exceptionally well, very light to handle and glide through the water easily and smoothly. I'll be quite happy to use them until they begin to fall to bits.

[Oldmeadow]

I'm not sure sorry but I have to say that I'm very impressed with the build.

[labr@]

Hi Len, it's always difficult to tell with photos but I notice that in the second photo the weave of the cloth is very apparent almost as if it was not fully wetted by the epoxy. If this is the case and water has worked into the cloth then the only fix may be sanding the cloth off and reglassing the section.

Some types of glass do not wet easily (learned that from bitter experience with a cheap source) with epoxy. Also contamination with water, dust or other substances may affect wettability.

When I was looking for ply to build a kayak I found the only good stuff was very expensive. I (and probably others) would be interested in knowing more about the red cedar ply.

[Toymaker Len]

Thanks for that advice Bob. I wouldn't be able to sand this back because the veneer is incredibly thin, much less than a milimetre. The story is that we had six sheets of 3mm red cedar veneer on 3mm ply good both sides. It was a misorder and should have been 3mm mdf formulated for laser cutting. We used to have a business which cut hopping kangaroos from 7mm red cedar veneered mdf and the venture into 3mm was to be an experiment in miniaturisation. Anyway the wrong material turned up which was a fairly crap mistake at $180 per sheet (our fault though) so I just wrapped them in a tarp and parked them in the shed. Not long after we sold the business and the sheets ended up leaning against my garage. So I had it in mind to start dabbling in making kayaks so I unwrapped the sheets even though they are a mill too thin and found that they were just starting to decay along the bottom edge and I had to do something with them quickly or lose them. There are a few good looking plans on the internet and I opted for the Chesapeake sixteen footer and bought the plans and book. Luckily I've got a big enough room downstairs at our place to do the construction in. It took about two weeks actual work spread over a month or so around last Christmas. Then I parked them under the house and set off for the Kimberly second week of march. After three weeks in Tassie we had to come home. I dragged the kayaks out from under the house, finished them with seats, lashing, varnish, kayak racks on the van and off we went kayaking around northern nsw and then up into southern queensland for a couple of months. My wife and I really like paddling up tidal creeks and coastal rivers just bird watching. These kayaks are so much lighter and easier to paddle than plastic ones. And they look pretty good too. I get a lot of people interested in them and surprised that I made them myself. I tell them that the stitch and glue method is really easy to do and what could possibly go wrong Ha ha ha. My partner will probably paint over the discoloured bits and we will keep using them until they start to fail. The all up cost of making them added up to about $500 each not counting the plywood. Next time I will be buying 4mm marine ply.

[ian]

Len
what brand of epoxy and glass did you use for your kayaks?

The problem could be the epoxy itself. Cutting the glass back to bare wood could be done if you are super careful.

[Toymaker Len]

I don't have the name of the epoxy any more as I gave the leftovers away. It was just a generic couple of litres from a local supplier called Trojan Fibreglass though. Something they package themselves from 300 litre drums so you could be right. As for cutting it back to the wood very very carefully...I am trying to imagine how that might go. I might be able to crack the skin and then get a fine chisel or a spatula in and peel the glass and epoxy off if it would come free. If there is too much frigging around involved it might be better to just start the next one and there are a couple of other mistakes which I could avoid the second time around. Also I have in mind to rig these two side by side into a little catamaran with a small jib and a main. The rigging could be carried on the roof racks and get pulled out on those days when there is a bit too much wind to be comfortable paddling. Not that that makes any difference to the blotches.

[ian]

Len,
My epoxy experience is building a couple of stitch and glue kayak kits sourced from Pygmy Boats (Pygmy Boats: Voted Best Wooden Kayak Kit (http://www.pygmyboats.com/index.html)) who, prior to closing their showroom in July this year, were located in Port Townsend, Washington State.
The epoxy supplied by Pygmy boats was System Three -- either System Three's General Purpose or SilverTip resins. these resins are mixed in a 2:1 ratio, so the mix ratio is nowhere as critical as West Systems which is typically mixed in a 5:1 ratio. I note that the epoxy sold by Trojan Industries is the more critical 5:1 ratio akin to that made by West Systems. I haven't studied Trojan's website in enough detail to determine if the Trojan epoxy is very similar to that made by West Systems, but suspect it is not.

Last year I fortuitously happened to be in Sydney at the right time for Sydney edition of the TWWS, so I took the opportunity of having a conversation with the Bote Cote epoxy people about the availability of System Three products in Australia. Their answer was that while neither System Three's General Purpose or SilverTip epoxy was not available in Australia, the Bote Cote epoxy was "the same formulation."


as to what to do with your kayaks,
I suggest that you do not reserve the hulls for use as part of a catamaran. To my mind the risk of catastrophic failure of one of the hulls is just too great.

What I think I am looking at in your photos is delamination of the glass fabric from the hull of one kayak.
Whilst I was out riding today -- I'm in a time zone 16 hours behind Sydney -- I recalled that I had a similar delamination issue with the three layers of 2" wide fiberglass reinforcing tape applied to reinforce the inside of one of my kayak's deck main stress point.
In my case, I was able to lift the delaminated glass with a sharp chisel and sand the residue back to good glass. If you use a very sharp knife to cut the glass and then a spatula to lift all the loose bits, you should be able to feather sand the resulting edge so that you can lay a fiberglass cloth patch over the delaminated sections.
To my way of thinking doing that is a much better option that having your partner cover up the damage using opaque paint.

[Toymaker Len]

Thanks Ian I like you remedy for delamination and that is probably the way I will go. I know the hulls are not designed to take the stress of a catamaran hull and I intend to make a very light weight underpowered rig if I do it at all. And I just noticed that the first photo is upside down. The epoxy I used was 1:2 and performed well in every other area. There are even a couple of deep scratches on the bottoms, from scraping over oyster shells in tidal creeks, which haven't led to any deterioration at all despite the glass being scraped and exposed to water.