Name the Substance

[Christian Williams]

I am replacing lenses on 1984-era Lewmar Superhatches and the sliding hatch.

The lenses are bedded in a black, tarry medium that dissolves easily in mineral spirits or PB Blaster. It looks like butyl rubber.

It's a sealer not an adhesive, but since the area of the hatch perimeter is large, makes a very secure connection.

It scrapes off the aluminum easily with a putty knife, in contiguous strips.

The visible seam, as you'd see it from above with the hatch in place, can be separated from the frame with a razor blade.

I'm pretty sure this black stuff isn't silicone, which clings like a bad girlfriend.

Maine Sail, last time around, doubted it was butyl.

I'd like to use it again, rather than silicone. But--what is it?

 

[GrandpaSteve]

I am replacing lenses on 1984-era Lewmar Superhatches and the sliding hatch.

The lenses are bedded in a black, tarry medium that dissolves easily in mineral spirits or PB Blaster. It looks like butyl rubber.

It's a sealer not an adhesive, but since the area of the hatch perimeter is large, makes a very secure connection.

It scrapes off the aluminum easily with a putty knife, in contiguous strips.

The visible seam, as you'd see it from above with the hatch in place, can be separated from the frame with a razor blade.

I'm pretty sure this black stuff isn't silicone, which clings like a bad girlfriend.

Maine Sail, last time around, doubted it was butyl.

I'd like to use it again, rather than silicone. But--what is it?

Maybe it is butyl though. See if a piece of butyl dissolves in PB Blaster.

 

[Loren Beach]

Over the years, we first replaced the foreword Lewmar #70 hatch and later the #20 vent hatch.
(The large hatch had a bent frame from before we bought the boat. )

I have noticed that both hatch lids have their lenses bedded in a pliable sealant, and it's interesting that my forward hatch will still show some indentation from a sharp fingernail into the black sealant edge, 20 years later. Interesting product.

You might want to ask Lewmar, or, closer to home, ask Select Plastics. Select installs new lenses into Lewmar frames when you send them your hatch lid. A friend of mine did just that for his '86 E-38-200. The result was "like new."

Regards,
Loren

 

[Kerry Kukucha]

I replaced the lenses on my hatches 8 years ago; the Lewmar frame had an integral rubber gasket that fit into a channel on the hatch frame, upon which butyl tape was afixed to hold/seal the underside of the lenses. There was a small gap on the top side between the aluminum frame and new lense (which was identical in size to the old one); sourced a 3M flexible window sealant from a commercial window shop to fill the gap. Hatches have been water tight and perfect ever since!

 

[lonokai]

Where is all this work accomplished?

Do you do all of this work at the slip? or, do you haul the boat out?

 

[Ian S]

Hi Christian. You are most likely dealing with polysulfide. Polysulfide stays very flexible for decades. I have re-bedded many a hatch and lenses and most recently i replaced all the lenses on my 90' 32-3. I have to say I have always had the most success with Dow 795. It is incredibly flexible (50% elasticity), UV stable, and has excellent adhesive qualities. Mask off the lens and frame with a quality blue masking tape (3m) when you apply your bedding. Denatured alcohol is your best solvent prior to full cure. You can perform additional clean up with a product called ID RED. this is a must have product and well known in the aviation industry for cleaning greases, waxes and even silicones from plastics and sensitive substrates including paints. dow 795 is also accepted as a bedding compound for aviation polycarbonates. Lastly The best scraper is a plexiglass scraper for removing excess bedding compound of any type. These are tricks I have learned from an aircraft mechanic friend and has improved my skills and the quality of my work markedly! Again plastic scrapers are of paramount necessity for all jobs around gellcoat and plastics!!

Good Luck. Cant. Ian

scrapershttp://www.jusntyme.com

 

[Rick R.]

Christain, as you know, we just did ours three days ago. I'd swear it is black butyl. I say that because of the way it is still plyable after nearly 30 years.

 

[Christian Williams]

What marine sealants identify primarily as polysulfieds? Anybody got a brand name?

Yeah, the general recommendation for plastic is Dow 795. And it's cheap.

But it's silicone, with different properties than the factory stuff that worked so well and came off so easily after 30 years.

 

[GrandpaSteve]

What marine sealants identify primarily as polysulfieds? Anybody got a brand name?

Yeah, the general recommendation for plastic is Dow 795. And it's cheap.

But it's silicone, with different properties than the factory stuff that worked so well and came off so easily after 30 years.

Life-calk(tm)
http://www.boatlife.com/lifecalk-sealant-tube-1oz/

 

[Rick R.]

The Dow 795 I use the other day is still very tacky. Maybe it will remain that way for many years as well?

3M 4000 UV Fast Cure Sealant is a polysulfide.

 

[Tom Metzger]

The Dow 795 I use the other day is still very tacky. Maybe it will remain that way for many years as well?

Dow says the 795 should be tack free in 3 hours. I suspect that number is for people who actually buy in-date tubes, though. :0

<cite class="_Rm">https://sweets.construction.com/swts_content_files/324/830431.pdf</cite>

 

[Loren Beach]

One note about sealing acrylic or lexan

Life Calk was referenced in this thread, and since this is about hatch lenses (or ports), there is a known problem with that particular product in contact with some plastics.
I found this out for myself when I sealed a white plastic cast vent base to the deck of our first boat and after a couple of years the white plastic base started coming apart. :0

I found this quote:
"The polysulfides, such as BoatLIFE's Life Calk or 3M's 101, bond to wood better than silicone does and also bond fairly well to metals and fiberglass. However, they can melt some plastics and acrylics, such as Lexan, and some vinyls can become softened by exposure to their solvents."

Here is a link to the article: http://www.goodoldboat.org/reader_services/articles/sealant.php

I have been using Boat Life LifeSEAL for sealing/bedding pretty much everything, including plastics. Good product. No leaks, either.

Regards,
Loren

 

[Ian S]

Hi Guys, If your 795 is still tacky, it is as previously mentioned, probably because it is out of date (there is a use by date on the tube approx. 1 yr from MFG), or it's extremely dry out. I assure all that commercial / industrial silicones are the correct material for bedding plastics. Contact the largest Hatch refurbisher in the US (Hatchmasters) And I believe they will confirm that they use dow 795 or a similar commercial silicone.
IMO polysulfide is the ONLY appropriate material for bedding deck fixtures that will not be permanent. Oh and don't kid yourself about what the word permanent means. Most hardware will be removed at some point in a boats life with the exception of maybe the Keel or deck joint. 3M 4200 (semi permanent,,, MAYBE??) and 5200 (totally permanent) will tear off the gelcoat and usually a layer of fiberglass before they let go. this is because they are polyurethanes. This for me includes through hulls. Life seal and life caulk are two totally different products to be clear. life seal ( I don't care what they call it) is basically a modified silicone polymer and life caulk is a true polysulfide. Let it also be known that polysulfides can and will attack many types of plastics. A good example is clutches made of plastic & glass resins ie. Spinlock.
Back to the uncured 795. it needs atmospheric moisture to cure just as polysulfide does. As a matter of fact wetting polysulfide is the best way to accelerate curing because it can take a long time to cure. A large bead of sulfide such that may be found between teak deck planking will still be pliable and occasionally even tacky after 2 decades. All that being said I assure you Christian that Dow 795 will produce excellent long lasting results. This not your typical silicone sealant. please nobody confuse these products with bathroom caulks. Lastly I believe that there was a period where lewmar did in fact make the initial bed with Butyl tape to set the lens and then finished the seal / side gaps with some type of proprietary sealant. You should retain a generous space / clearance from the lens to the frame so that not only can the lens expand and contract but the wider / larger bead of sealant the more flexibility it will have. I have some hatch lenses I replaced 15+ years ago with 795 and the seals are perfect. the lenses are of course scratched and beat up again but the sealant is in perfect condition.

I hope this helps. Capt. Ian

 

[Rick R.]

Hi Guys, If your 795 is still tacky, it is as previously mentioned, probably because it is out of date (there is a use by date on the tube approx. 1 yr from MFG), or it's extremely dry out. I assure all that commercial / industrial silicones are the correct material for bedding plastics. Contact the largest Hatch refurbisher in the US (Hatchmasters) And I believe they will confirm that they use dow 795 or a similar commercial silicone.
IMO polysulfide is the ONLY appropriate material for bedding deck fixtures that will not be permanent. Oh and don't kid yourself about what the word permanent means. Most hardware will be removed at some point in a boats life with the exception of maybe the Keel or deck joint. 3M 4200 (semi permanent,,, MAYBE??) and 5200 (totally permanent) will tear off the gelcoat and usually a layer of fiberglass before they let go. this is because they are polyurethanes. This for me includes through hulls. Life seal and life caulk are two totally different products to be clear. life seal ( I don't care what they call it) is basically a modified silicone polymer and life caulk is a true polysulfide. Let it also be known that polysulfides can and will attack many types of plastics. A good example is clutches made of plastic & glass resins ie. Spinlock.
Back to the uncured 795. it needs atmospheric moisture to cure just as polysulfide does. As a matter of fact wetting polysulfide is the best way to accelerate curing because it can take a long time to cure. A large bead of sulfide such that may be found between teak deck planking will still be pliable and occasionally even tacky after 2 decades. All that being said I assure you Christian that Dow 795 will produce excellent long lasting results. This not your typical silicone sealant. please nobody confuse these products with bathroom caulks. Lastly I believe that there was a period where lewmar did in fact make the initial bed with Butyl tape to set the lens and then finished the seal / side gaps with some type of proprietary sealant. You should retain a generous space / clearance from the lens to the frame so that not only can the lens expand and contract but the wider / larger bead of sealant the more flexibility it will have. I have some hatch lenses I replaced 15+ years ago with 795 and the seals are perfect. the lenses are of course scratched and beat up again but the sealant is in perfect condition.

I hope this helps. Capt. Ian

Excellent reply Ian.

I'm not surprised the 795 I used was still a little tacky after three days. Tony (from Select) told me it would take 21 days to fully cure. A PDF from Dow I read said the same. Regarding the need for moisture to help, I will be putting the hatches back on the boat in the next few days (when the new hinge hardware and handles I ordered arrive).

note: do not purchase fresh 795 then wait a year to use it so says the Oracle err.....:nerd:

 

[Christian Williams]

OK, I conclude that the original black bedding of the lenses is indeed butyl tape. If it walks like a duck....

But this time around I will re-set the lenses in only one course of butyl tape.

Then I will use 795 only for the 1/8th inch expansion gap, applied separately, from the top, and last.

Hatch lens plastic is held down securely by the hinges and dogs, anyhow.

This time I am also having a new sliding hatch heat-formed out of 1/2" acrylic. More on that later. It is proving expensive.

 

[GrandpaSteve]

Where do you find someone to fabricate the hatch Lexan (or whatever the appropriate material name is)?

 

[Christian Williams]

uality Plastics, in Ontario

Here, the nearest facility is California Quality Plastics, 909-930-6635, in Ontario, about an hour's drive from me.

It's looking like $250 for the heat-forming, $100 for the custom "mold"--and buying a 4x8 sheet of 1/2" inch acrylic ($350). But I can use the rest of that piece for the hatches and port lenses.

Heat-forming isn't a big deal, just beyond the capability of neighborhood plastics fabricators.

My guy says that if the curved hatch was 3/8ths, we could probably bend it over the Ericson frame without heat. Heat from the sun would then eventually make the bend permanent.

 

[Rick R.]

Where do you find someone to fabricate the hatch Lexan (or whatever the appropriate material name is)?

Steve, if you're doing the two Lewmar hatches, go to estreetplastics.com or call them ( Mike). I purchased a 24x36 sheet of 1/2" acrylic #2064 transparent grey. This was enough to cut out both hatches and cost $69

 

[GrandpaSteve]

Steve, if you're doing the two Lewmar hatches, go to estreetplastics.com or call them ( Mike). I purchased a 24x36 sheet of 1/2" acrylic #2064 transparent grey. This was enough to cut out both hatches and cost $69

Thanks Rick! Do you cut it with a router?

 

[Rick R.]

Thanks Rick! Do you cut it with a router?

You surely can. I took it to my local plastics guy to do it.