torn canvas on cabin top

[Doug Tutty]

I'm considering purchasing a 37' Stevens Ketch. One of the things it needs is attention to the cabin top as the canvas has torn 4" at one corner. Underneath looks like wide T&G mahogany but I don't know yet. Underside is 4" T&G mahogony, varnished. Decks and soles are teak, the only white 'deck' is the cabin top. Structure seems sound; can jump on it, etc. Yet to be surveyed, but it will be!!!

My first question is, what is the purpose of the canvas? There doesn't appear to be anything between the canvas and the wood.

In this repair, I want to minimize 'modern' materials re chemical exposure for wife. Cabin top ie about 10' long by 5' wide.

Is there a way to just repair this part of the canvas or do I have to look at the whole top?

[Thad]

You can patch canvas, bedding with paint and tacking or gluing, painted it will not look bad but it will always look like a patch. The canvas is for watertight in this use although in lighter built boats with canvased decks it also has a structural purpose, if you believe L. Francis. Usually a house top will not have nearly the number of cleats and rails on the canvas to remove and replace if you are going to recanvas, and it is a fun job.

[Doug Tutty]

So to patch: paint under the edge of the existing canvas, tack down the edges, then paint over and cover with a piece of heavy canvas, tacked all around and paint that?

If I were to redo the whole cabin top, I would consider teak to match the rest of the deck, both in looks, functionality, and maintenance. How big a job?

What is a good book on wooden boat maintenance, preferably one book that covers all the usual requirements well rather than some good and some bad ideas, because I wouldn't be able to differentiate, and I want to minimize the number of books since we'll be living on the boat year-round.

[Nicholas Carey]

Originally posted by Doug Tutty:
So to patch: paint under the edge of the existing canvas, tack down the edges, then paint over and cover with a piece of heavy canvas, tacked all around and paint that?In my experience, patching torn or split canvas looks ratty, doesn't work all that well and is a temporary expedient at best—because the tear or split you're patching is usually a symptom of some other problem like a sharp edge that caused chafe or rotten canvas or wood under the molding at the corner of the house where the canvas is torn and peeling -- that's probably why the canvas let go in the first place.


If I were to redo the whole cabin top, I would consider teak to match the rest of the deck, both in looks, functionality, and maintenance. How big a job?Well...if you're going to replace the house top with a laid teak teck, it's a big job. Housetops are also not usually teak as people don't ordinarily walk on them. Teak is also heavy and using on the housetop adds weight up high where you don't want it.

Replacing the canvas is the way to go—a canvas deck should last for 15-20 years or so.

Replacing the canvas should be pretty straightforward and you could probably do the entire house top fairly quickly.

One other option to consider would be to replace the T&G subdeck with a marine ply skin, covered with dynel and epoxy. Done right, it looks a lot like canvas, adds a lot of rigidity (something older boats often need) and avoids leaks.

However...

There's always a however...to do this, the surface must be developable, which means it needs to be a conic section, like a cylinder or cone. If it's not, the plywood won't conform to the curve (it can only bend on one axis.)

Prep Work

Remove all hardware and trim from the house top. This means removing hatches, skylights, winch bases, cleats, blocks, mast boot flange, etc. Everything mounted on the canvas has to come off. Note that if the mast comes through the housetop, you might want to remove the mast as well. That or plan on providing a cut in the canvas to go around the mast and hand-stitching a flat-felled seam to close it up when you put the canvas down.

You might want to photograph the housetop prior to removing all this stuff so as to facilitate its reinstallation. You might want to make measurements as well that you can use to locate any hardware that isn't through-bolted.

When you're done the house top should be a — dare I say it? — blank canvas :D

The edges of the canvas should be exposed all the way around, either stapled or nailed in place. (n.b., while all this stuff is off the boat, this would be a good time to turn the basement into a varnish shop and refinish the removed items.)

Strip off the canvas and remove the nails/staples holding it in place.

Check for rot, signs of water incursion, etc. Make any necessary repairs (this is where it could get time consuming). Ensure the all edges are rounded where the canvas slides over. Sharp edges will chafe through the canvas.

Consider filling with epoxy/silica any screw holes from hardware that's just screwed in place and not through bolted and through-bolting it instead. This is a good time to drill the through holes for that hardware now and installing any necessary backing plates needed.

Since your housetop is T&G mahogany, you won't be wanting to bed the canvas on it. You might want to put down a layer of Irish felt first, though. It helps to minimize chafe and print-through of the T&G seams, and it gives the deck a little padding. Irish felt is tar-impregnated felt, rather like roofing paper. Some people don't like it; others think it the bee's knees.

Get plain, undyed cotton canvas wide enough to cover the housetop. Ideally it should be pre-shrunk. You might want to stretch it out flat, pour hot or boiling water on it to shrink it and let it dry in the sun prior to Installation. Rememember to allow for shrinkage when sizing the canvas if you do this. It's important to allow for and deal with any shrinkage one way or another: if you don't, you're likely to wind up with tension tears in the canvas. When it shrinks, something's got to give.

Canvas Installation

Installing the canvas is about the same as putting together an artist's canvas for a painting...and not a whole lot different. To install it...

Lay it out on the house top, lining up the warp and weft so it looks right. Don't worry about openings in the house top right now -- those will be cut after the canvas is down.

Using copper tacks or monel staples, tack the canvas (one fastener) at the center front of the house. Pull the canvas the right amount of snug and do the same at the after end of the house (if the companionway is in the way, tack it on either side of the companionway.

Repeat this exercise at the center sides of the house.

Repeat this criss-cross fastening until the canvas is completely tacked down, alternating house sides and house ends, working around the house in a consistent pattern. It's not unlike tightening head bolts in a criss-cross pattern to ensure uniform torque.

The point of this exercise is to get a uniform tension on the canvas without wrinkles and with the warp and the weft aligned pleasingly.

Once the canvas is down, you need to cut any openings in the canvas, leaving enough excess so you can pull it snug and tack it down as well. If the opening is circular, you'll need to cut darts in the flaps so it lays down smoothly.

Looks nice, doesn't it?

Painting the Canvas

The point of painting the canvas isn't to put a film on the surface, but to fill the weave with paint so it's waterproof. So...

Did I mention the canvas has to be kept dry while all this is going on?

Start with extremely thinned conventional (alkyd) enamel (no primer) in the Color of Your Choice. A lot of people here like Kirby Paint's products, but Interlux, Petit/Z-Spar/Woolsey or Epifanes' products will work perfectly fine as well.

A good place to start might be 1 part enamel, 5 parts thinner. Paint the new canvas with it and let it dry. Do 2-3 coats like this. You won't see much build up. That's the point. You want to get the paint into the fibers, not on the surface.

Reduce the amount of thinner a bit and repeat.

Repeat this process — reduce the amount of thnner a bit, do a couple of coats — until the canvas is saturated with paint. The last coat should be near fully strength.

What you don't want is for the canvas to look 'painted'. It should still look like canvas and it shouldn't be glossy. At best, it should be semi-glossy.

If you wind up with too much paint, or a film on the surface, it will crack and you will get water incursion (aka leaks). Which, in turn, leads to rotten canvas which leads to...doing this again.

Don't do that.

Reinstalling Hardware, etc.

Through-bolted stuff is easy to locate. Using a drill of Appropriate Size, punch through the canvas from beneath, using the existing holes. If the hardware is screwed in place, you may be better off drilling new screw holes (you did fill the existing holes with epoxy?).

Don't forget to bed everything well. Dolphinite is a fine bedding compound for this use. Avoid 3M 5200 like the plague. It's a glue, not a sealant. If you use something modern, use a polysulfide like 3M 4200 or Sikaflex instead.

That's about it.

Painting the canvas, all things considered, probably takes more time than anything else, because there's no good way to hurry the painting.

Good Luck.

[ChuckG]

Maybe some of the old hands remember a product for covering canvas that was for all the world identical to white Elmer's glue. I seem to remember the name "Flexideck" but a Google search doesn't turn up what I'm thinking of.

It was a water-soluble latex product, that filled in the cnavas material and provided a flexible and durable finish that survived a bit of abuse on a fishing boat wheelhouse and cabin trunk top.

Anybody seen that around lately?

[Nicholas Carey]

Originally posted by ChuckG:
Maybe some of the old hands remember a product for covering canvas that was for all the world identical to white Elmer's glue. I seem to remember the name "Flexideck" but a Google search doesn't turn up what I'm thinking of.

It was a water-soluble latex product, that filled in the cnavas material and provided a flexible and durable finish that survived a bit of abuse on a fishing boat wheelhouse and cabin trunk top.I know what you're referring to (but I can't come up with the name offhand either). Googling....got it. Arabol.

It's a casein-based lagging adhesive and it's used to lag the canvas down to the sub-deck, but not to fill the weave—that's still down with paint.

Borden's out of that business these days; Arabol is no more.

The current replacement is Childer's Chil-Seal CP-50A HV2 Coating (http://www.fosterproducts.com/Images/childers_tds/CP-50A_HV2.pdf) (PDF, 129k), High Viscosity Coating and Adhesive for Finishing and Adhering Canvas and Other Lagging Cloths over Thermal Insulation,
Military Specification MIL-A-3316C, Class 1, Grade A

It essentially the same thing as Arabol.

However, as noted in my earlier post, you don't want to lag down the canvas over the T&G subdeck. You want to allow the subdeck to work underneath the canvas. If the canvas is bonded to the T&G, it will develop cracks at the plank edges.

[WFK]

The other name for flex-a-deck, was cover-deck,and fisheries supply in Seattle use to carry it.
In my opinion the way to go here is remove the old canvas, cover the existing wood house top with 2 layers of 1/4" marine ply or even less, maybe 3 mm. With some spiling where the joints meet,it will bend. Cover this with cloth and epoxy and you got your self a bullet proof cabin top, with no changing of the appearence inside the cabin.

Bill

[Doug Tutty]

Thanks all, that's great. Redoing in canvas seems easy enough. I've got the canvas. I bought a whole bolt of it when we found that Jane could only tolerate cotton and silk. I pre-shrunk the whole bolt, ironed it, and rolled it up again. Compared to that, cavasing a deck sounds easy.

I can't use Irish felt due to the tar. Is there something else; there's nothing there now.

The T&G is close-seamed; I know its T&G because I've seen an end-view through a tear in the canvas. From the top it looks like a table-top.

Since its so late in the season, I'll probably patch it this fall and redo it in the spring at whatever priority the surveyor recommends.

I can't use casiene glue; I'm allergic to milk.

I can't use marine ply; my wife is allergic to glue.

Thanks for the advice re the teak; I'll save the weight.

Since the cabin top looks so close-seamed and doesn't leak despite the tears in the canvas, are there alternatives to canvas? For example, the decks of Muscoka run-abouts are bright-finished mahogany with white caulking; looks very spiffy. What keeps it from leaking? If you don't put teak there because one doesn't usually walk there, couldn't one do a bright top like that?

[Carlsboats]

Nicholas Carey's "how to" is thorough and very helpful, but I disagree with one detail. He says that you should keep the canvas dry throughout the process. To the contrary, I was brought up to believe that you put the canvas down with tacks, then dampen it (to make it shrink), then give it a coat of very thin paint while it is still wet.
The water works its way out through the prime coat of paint (moisture vapor will go through any paint, with time), but the paint, one it dries, keeps the canvas drum tight. I have done several canvas decks this way, with nary a failure. Most recently, I used 12-ounce plain cotton (from Defender Industries in Waterford, CT) over a plywood deck, and it came out without a trace of a wrinkle. By the bye, you can get real cotton canvas in very wide pieces -- 100" or more -- which means you can do most decks without seams. That's a big plus.

[Ed Killian]

Very helpful thread, guys - thanks especially to Nicholas Cary for the time he put into his answer. Been thinking about glassing the top of my '37 Richardson but wasn't looking forward to it. Just doesn't seem right to put that elegant old lady in something that hard. Seems like the orignal canvas approach will work just fine and be a lot easier and more fun to work with
Ed