CD36 hull liner to hull bonding weirdness

[Troy Scott]

Folks,

I've been working to install all new seacock backing plates. I'm using 1/2" FRP, and I'm bonding the new plates in parallel to the outer surface of the hull. Today I worked under the lavatory in the head, where there is a 3/4" seacock for the toilet intake and a 1 1/4" seacock for the lavatory drain. To accommodate these two, the factory cut out a portion of the hull liner about 6" by 12" so the plates could be mounted directly on the hull. They "sealed" the space between the hull and liner around the perimeter of this cutout, using what I believe to be a mixture of polyester resin and gypsum. Now there is a gap of about 3/16" between the liner and this filler. I suppose maybe the filler shrank, or possibly as the the liner aged it curled inward strongly enough to separate it from the filler. The hull is definitely not deformed or "bulged out" in this area. As an experiment I tried using a boat stand to push the hull in enough in this area to close the gap. I could not apply enough force to close the gap, and the hull looked deformed when I tried. I do not believe the hull is the problem. I'm thinking I'll mix up some epoxy spooge and fill this gap. After that I'll do a little filling, sanding and painting to make this area look better than new, and install my new FRP backing plates. At least that's the plan unless someone out there convinces me why I shouldn't. How about it folks, have any of you noticed this kind of hull to hull liner disconnect?

[Duncan]

It seems to me I saw some discussion of this "mish-mash" on the pages at S/V Fenix. I recall he said that they used to use asbestos, so I'd be careful about dislodging any of it.

I suspect the gap is more a matter of appearances than an indication of any requirement for bonding or sealing. Spooging it over and sealing it with a layer or two of glass will probably make it look nicer, though?

[Dalton]

but they left it totally open. I'd probably pull it out and let it breath in there. And if it is asbestos, can't it be removed safely? gloves, mask, heavy duty Ziploc bags.

Greg

[Dalton]

An interesting thing happened this year on launch. The engine intake thru-hull weeped a little, a couple of drops an hour at only one spot, from between the hull and the 3/4" marine ply backing plate. At first I was concerned. But then it occurred to me that, like a wooden boat the plate would soon swell with the moisture and sure enough it stopped after a few days. FWIW.

Greg

[Andy Denmark]

There's a good thread on this subject in the archives. Bottom line; wet plywood will eventually rot while FRP will not. I've replaced all plywood backing plates with 1/2" vinylester from McMaster Carr. Most of the plywood backing plates I removed were rotted or well on the way (after 25 years -- not too bad, I'd say).

FWIW
________
PLYMOUTH ARROW HISTORY

[Cathy Monaghan]

Folks.........They "sealed" the space between the hull and liner around the perimeter of this cutout, using what I believe to be a mixture of polyester resin and gypsum. Now there is a gap of about 3/16" between the liner and this filler.......

Hi Troy,

Cape Dory used Dolphinite Bedding Compound to bed or seal nearly everything on our boats. The hull does alot of flexing while underway and it's not unusual for any seals, anywhere on the boat, to work free after time. That, and the fact that the stuff eventually dries out, is why hardward needs to be rebed every 5+/- years. Anyway, it sounds like the stuff has dried up and shrunk, so you just need to clean the old stuff out and reseal the area.


Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

[Troy Scott]

I would be surprised if asbestos was cheaper than gypsum in 1987, and I think also that by 1987 it was a well-known health risk. And surely milled glass fibers (also cheap) were available. Why would they have used asbestos? I certainly hope that's not what's in there. I have had occasion to grind some of that stuff out here and there. While I usually wear a breathing system when I make dust, I like most people am not as diligent as perhaps I should be. If I had any suspicion that I might have been grinding asbestos I would have either not done it, or I would have taken even more precautions.

[Troy Scott]

Cathy,

There was a lot of good Dolphinite bedding compound in my boat. Practically all the Dolphinite I have cleaned away is in excellent, pliable condition. Very little was compromised or leaking; what was leaking appeared to be poorly bedded hardware added after the boat left the factory.

The material in question is not bedding compound. It is hard, resin-based structural stuff with characteristics similar to the better quality fiber-filled Bondo. Since it is probably polyester based, it is reasonable to assume that it has shrunk.

[Duncan]

...by 1987...asbestos? I certainly hope that's not what's in there...

This quote suggests you may be ok, based on 1987.

A cautionary note: In the era that this boat was built (1978) it was quite common to use asbestos as a filler in polyester resin to make "Mish-Mash". This type of "Mish-Mash" was used extensively in boat building. In my Cape Dory it is used as above and to set the interior liner in the hull (emphasis added) and also as the principle hull-deck joint bonding material. When I first worked for Sam Morse (1978) we were using asbestos to make mish-mash. It was not too long afterwards that word came down from on high about the "dangers" of asbestos, thereafter we stopped using asbestos and started using industrial grade talc. S/V Fenix page

NB. Fred does not say specifically that CD used asbestos to make mish-mash, just that his experience was that this was common practice at a certain point.

[Troy Scott]

I have now finished rebuilding the area in question to "better than new" status. When painted it will be as beautiful as "the space under the lavatory where two seacocks fit" can be.

But I'm still concerned about the possibility of having inadvertently breathed asbestos. I'm thinking I could send a sample of the mish-mash to a biochemist friend in St Louis for analysis. Thoughts?

[Troy Scott]

Folks,

I have heard from Dave Perry WRT the asbestos question. Here is what he wrote:

"You are pretty accurate about the gypsum powder mix with polyester resin, making a polyester bonding compound, used for deck / hull joints and attaching liners, etc. No asbestos was known to have been a part of this material."

Needless to say I am relieved.

[fenixrises]

...or the boy who cried wolf.

Asbestos and its hazards are known? Well sort of. It is like the hazards of silicon breast implants. Even though silicon is also made into artificial joints, with no problems.

As for asbestos, I suspect that an occasional inhalation of a few bits of dust will not immediately cause you any problem. Remember the people who had asbestos based problems worked with the material on a daily basis for many, many years and often did not use any form of mask.

If your filler has a dark gray almost black look about it then it is almost surely asbestos. I know because I mixed 100's of lbs of this stuff into poly resin to make filler. It works great because the fibers are longish and add a fair bit of strength to the resin.

The danger I was told is because the fibers tend to have "hooks" in them. And just like fish hooks the fibers hook into lung tissue and stay forever. Glass fibers on the other hand do not have hooks. They will actually slowly work to the surface, it may take years. Many military people wounded by flying glass particles have had the tinyest of particles surface years later.

Milled glass fiber is also a good filler, very strong, but it does not make a good "butter" like asbestos. Industrial grade talc makes a good filler but I do not think it is a strong as asbestos but the "butter" is better than milled fibers. I often used a combination of milled fiber and talc to get the best of both.

Take care and breath easy,
Fred

[Troy Scott]

Fred,

Well it is dark gray, and very tough. With respect to Dave, I think I will send some of it off for testing just to be sure. In the meantime, all you other CD folk, don't grind any of this stuff you see. In my boat this is the filler/bonder in the hull to deck joint and it is the material CD used to fill the gap here and there to attach the various parts of the hull liner (where there is one).

My boat had a huge "donut" of this stuff around the direct-overboard seacock next to the toilet. There is a space of maybe 1.5 inches between the hull and liner there. The factory(?) cut a nice round hole in the liner, maybe 7 inches in diameter, to provide access for mounting the valve on the hull. They filled the gap with this mish-mash/butter and shaped the inside wall of the resulting doughnut (more or less perpendicular to the hull) to look nice and painted it white to match. BUT..., the huge, heavy (probably 7 or 8 pounds) doughnut came loose. When I removed that valve the doughnut slipped down about a foot and jammed into a space that hasn't seen the light of day since 1987. Luckily I was able to work it around to a spot in the bilge where I was able to pull it out. I threw it away. It was immediately apparent to me that I could easily mold a strong, lightweight FRP part to serve that purpose. But I'm eliminating that valve anyway; no more direct discharge for us.

CD also used this material to correct the shape of the portlight cutouts as well as fill the gap between the cabin ceiling and the outer wall/deck where the portlights are mounted. I can't imagine why the cutout was so sloppy, requiring someone to go back and, using a waxed portlight as a mold, recreate the shape the window fits into.

Honestly, if CD had used this material (or something like it but better) to replace a 1.5 inch cylinder of wood core everywhere a fastener or hole was anticipated to pass through the deck, very few of us would have experienced any wet core troubles.

WRT the asbestos fibers having "hooks", I've heard the same thing. The "hooks", combined with the particular dimensions of the fibers, make our lungs particularly susceptible to being invaded and "occupied" by these loose fibers. I've also heard that once the fibers are embedded in resin that they are harmless. I am not enough of an expert to comment. Now, another popular (more modern) thickener is fumed silica; one brand name is Cabosil. This stuff is everywhere. I've heard that it is sometimes even used as a thickener in candy. I've not observed this under a microscope, but I'm told that this stuff looks like billions of tiny Ss. When mixed in resin, they quickly give the material a mayonaise-like quality as the Ss link together. They add almost no bulk. This fumed silica is probably harmless, but there is a small voice in the back of my head that occasionally says "maybe not..."