Painting over cascover

[katie777]

Hi, we have a 40s/50s ex-naval pinnace with a cascover sheathed (mahogany) hull. The sheathing is in good condition and the hull is good as far as we can tell (it's double diagonal so we obviously can't inspect the outer layer). For the first time in ten years of ownership, we have taken the hull right back to the cascover and now have the tricky task of working out what to paint over it! Has anyone found an option that works well below the waterline?
There are a few wrinkles along plank joints, has anyone tackled these successfully?
We're not looking to remove the sheathing! Just make good the best way we can ?

 

[srm]

Way back in the 70's my first boat was a plywood catamaran with cascover sheathing to the gunwales. I repaired a few damaged patches with glass mat and polyester resin and applied antifoul.

Probably not the best way to do it, but I was young and even more foolish then. As far as I am aware it lasted the life of the boat - she broke from her mooring and was smashed on a rock breakwater around 20 years later, long after I had sold her.

If faced with the problem now I would use epoxy resin and glass cloth for making good. Painting should not be a problem, but perhaps an epoxy primer first. Just a suggestion.

 

[AntarcticPilot]

I'm sure everyone knows, but cascover sheathing is nylon impregnated with resorcinol resin.
This Overpainting 'Cascover' -The Official NORFOLK BROADS FORUM is interesting and might give some pointers.

 

[wrr]

Way back in the 70's my first boat was a plywood catamaran with cascover sheathing to the gunwales. I repaired a few damaged patches with glass mat and polyester resin and applied antifoul.

Probably not the best way to do it, but I was young and even more foolish then. As far as I am aware it lasted the life of the boat - she broke from her mooring and was smashed on a rock breakwater around 20 years later, long after I had sold her.

If faced with the problem now I would use epoxy resin and glass cloth for making good. Painting should not be a problem, but perhaps an epoxy primer first. Just a suggestion.

Hi, we have a 40s/50s ex-naval pinnace with a cascover sheathed (mahogany) hull. The sheathing is in good condition and the hull is good as far as we can tell (it's double diagonal so we obviously can't inspect the outer layer). For the first time in ten years of ownership, we have taken the hull right back to the cascover and now have the tricky task of working out what to paint over it! Has anyone found an option that works well below the waterline?
There are a few wrinkles along plank joints, has anyone tackled these successfully?
We're not looking to remove the sheathing! Just make good the best way we can ?

I have had a Cascover hull blasted. I inserted a wide bore needle into any raised areas and injected Cascophen via a second needle, thereby expelling any air. I then ironed the area flat using a ski waxing iron protected with aluminium foil. The blasting raised the nap of the fabric which then consumed 25l of Primocon in 3 coats on a 10m hull. All is well and antifouling is adhering 3 years later. Any patches can be covered with nylon mesh or Kevlar and Cascophen.

 

[Poignard]

The plywood coachroof of my Twister had been sheathed with what I think was Cascover when she was built in 1967. A few years ago I noticed it had become detached from the plywood in some places allowing water to creep under it so I decided to take it all off and re-sheath with glass cloth and epoxy. A lot of the Cascover sheathing was hard to remove which is a tribute to the product and to the yacht's builders (Uphams Ltd, Brixham)

 

[AntarcticPilot]

I understand that the resorcinol resin used for cascover sheathing is still used to bond weatherproof and marine plywood. It has better UV resistance than epoxy, and for some application sis superior to epoxy, but is not so widely useful.

 

[Gary Fox]

Check there are no secret puddles of water hiding between the textile and the timber.
I had a couple of surprises today on Marihøna, scraping around I popped a bubble of fresh water, it could have been there for years.
Sandwiches WILL cause rot unless you physically take action.
Slightly different boat, my deck is laid pitch pine. Hans Jolivet, a previous owner, covered the laid deck over with Sikaflex, then sheets of plywood, then topped with glassfibre. I'm sure it seemed like a good idea at the time, and he made a really good job. Not an ideal long term solution.
Thank your lucky stars it's not triple diagonal
I have carried out maintenance on 'Thais', a British Powerboat Company air sea rescue launch, also an un-named MTB. both 1940's built, and a random small DD pinnace; don't be shy of modern methods and substances, because your boat was not designed with long term maintenance considerations. If you can scrape out dry gaps and slits, be 100% sure there is no fresh water lingering, and everything is dry as a bone: literally spurt some Sika 291 (or no-name equivalent) in there, her structural strength will probly go up as well, happy days!

 

[Tranona]

Owned a Cascover sheathed boat for getting on for 40 years. first you need to check whether it is just Cascover (the cloth weave is visible when stripped of paint) or whether it has the additional Vinyl coating before painting. Above the water on mine was vinyl and below uncoated as I discovered when having it blasted. The vinyl did not like it and balled up leaving a poor surface. The underwater nap was raised as described in post#4 except in a few areas where I think it had been skimmed with epoxy filler in the past. advice from Wessex Resins (10 years ago when there was still a guy who had experience of Cascover) was fair the topsides with epoxy filler - I used International Watertite - Prekote and Toplac. Very successful. Underwater, again as per wrr above primer (I used Jotun Vinyguard, half the price of Primocon) and antifoul.

Over the years I carried out a number of localised repairs very successfully with epoxy and glass cloth, although my boat was plywood and very stable. Original sheathing was done in 1963 and still sound when I sold the boat in 2019.

 

[katie777]

Really grateful for so much really helpful advice. We really weren't sure what we needed to use but underwater primer and antifoul sounds like a great way forward.
We will attempt to inject and iron the wrinkles in the way you describe wrr.
Thanks all, invaluable advice. I'll update this post to let you know how we get on, we have our work cut out! ??