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Old 31-08-2015, 17:13   #1
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Butyl for sealing portlights and other questions?

We've got a total of 8 lovely old bronze portlights mounted to the hull of our boat which I'm in the process of removing and refurbishing. There was a bit of a design flaw with mounting of the portlights in that they were mounted through the solid fibreglass hull and through the 1/8" plywood lining on the inside. All very well and good, except that the design of the portlights means they seal on the inside of the hull, not the outside. No doubt silicon was used in the past to seal the gap around the hull cutout and portlight frame, but it gave up the ghost long ago and the flaw in design is that once the ply gets wet (which it will because there isn't an effective seal between hull and ply) and starts to rot it then turn allows more water leakage (which eventually works its way down the inside of the hull and proceeds to rot the bottom of the chainplate knees, but that's another story!)

Anyway, I'm thinking butyl tape could be the answer, as it maybe/perhaps/will ooze into the gaps between portlight and hull and hull and ply when the portlight is bolted back in place. The only problem is I don't recall ever reading if this has been done or is advisable??? Oh yeah, some of these portlights can submerge temporarily on a decent angle of heel, just to add to the fun! Did I also mention they're opening types as well? Fortunately the window seals seem to work pretty good!

On the subject of seals, is EPDM sponge a good sealing rubber? I'm trying to source 1/4 x 1/4 sealing in Oz and not having much luck other than EPDM sealing in this size. The existing stuff is still in reasonable condition but is solid rubber and quite firm.
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Old 31-08-2015, 17:16   #2
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Re: Butyl for sealing portlights and other questions?

You'll get lots of good advice. CF has helped me many times with great suggestions I had not thought of. Collective wisdom. To make the advice even better how about a couple pics to better understand the problem although your description was pretty good.
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Old 31-08-2015, 17:29   #3
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Re: Butyl for sealing portlights and other questions?

Are you saying the portlite flanges are on the inside of the boat? No trim rings outside? I would trust a ton of caulking more than a tape type of product in that situation, but some people here swear by butyl...
I like to put so much caulking on that It comes out everywhere when tightened and forces it self into screw holes etc.
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Old 31-08-2015, 17:46   #4
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Re: Butyl for sealing portlights and other questions?

Are you sure the rubber seal is solid? Lots of the replacement seal is solid stock but I think the oem stuff had a hole in the middle. It's also hard to get solid stuff that is soft enough. The hole in the middle of the oem gave it some give and it seals better with less pressure from the wing nuts.
Gray sillycone is a bit more firm than all the others and it makes a pretty good seal if you fill up the whole channel in the port with it.
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Old 31-08-2015, 18:12   #5
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Re: Butyl for sealing portlights and other questions?

Quote:
Originally Posted by Cheechako View Post
Are you saying the portlite flanges are on the inside of the boat? No trim rings outside? I would trust a ton of caulking more than a tape type of product in that situation, but some people here swear by butyl...
I like to put so much caulking on that It comes out everywhere when tightened and forces it self into screw holes etc.
Yes. The only place compression occurs for a sealant is between the bronze portlight and the inside of the hull. The outside trim piece can only seal the screw holes at best.

I am considering a hybrid solution with caulking AND butyl. My objective is to seal the edges of the ply, the gap between ply and hull and maybe screw holes as well something that will survive all the different expansion coefficients and (presumably) flexing going on. Even though the boat is 30+ years old, the rot and leakage started very early on from what I can tell so the original silicon sealant either didn't completely seal let go fairly early in the piece.
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Old 31-08-2015, 18:43   #6
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Re: Butyl for sealing portlights and other questions?

Good info here from Mainesail on using butyl in a port install
Installing New Found Metals Stainless Portlights Photo Gallery by Compass Marine How To at pbase.com
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Old 31-08-2015, 19:14   #7
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Re: Butyl for sealing portlights and other questions?

I have seen with good results a combo approach for portlights using butyl and packing seals. Buy bulk roll packing seal (like stuffing box stuff but smaller. Put the butyl on the inside and the packing seal surrounding it. In that way as you tighten the flange the butyl squeezes and fills in all the space but the gasket keeps the butyl from all squeezing out over time.

That's why a picture would be good because I am having a tough time visualizaing your problem.
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Old 31-08-2015, 19:42   #8
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Re: Butyl for sealing portlights and other questions?

I have purchased butyl tape from several sources and compass marine has the best, some are not what I call butyl tape FYI!!!
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Old 31-08-2015, 19:59   #9
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Re: Butyl for sealing portlights and other questions?

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Originally Posted by sartorst View Post
I have purchased butyl tape from several sources and compass marine has the best, some are not what I call butyl tape FYI!!!
So true. The stuff mainsail sells seems very similar to a glazing butyl (although I'm no expert, so could be wrong on this). The stuff I use (because it's all I can get locally) is used primarily to join and seal dam liners but it does the job. I usually need to double it over to get enough thickness when sealing against non skid because it's thinner than the mainsail product.

On the other side of the coin, butyl self amalgamating electrical tape (which I use a lot of) is great for it's intended purpose but would be totally unsuitable for anything we're discussing here.

Here's an photo of the actual portlight and the horrible way it seals against the ply (and the resulting outcome after many years!)....



On a side note, they polish up very nicely after a process of removing the old clear coat then brushing with an 80 grit nylon power brush and then soaking in vinegar and salt solution (makes me feel hungry for chips!) and then finally polishing on a buffing wheel. I'll probably forgo the last step because I think I'll let them get a natural patina as polishing is just the pits and clearcoat just looks plain nasty once it gets scratched and damaged (which happens instantly around the hinges and dog bolts)
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Old 31-08-2015, 20:14   #10
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Re: Butyl for sealing portlights and other questions?

You need to re-establish the plywood first. Look for "Git-Rot" and "Gluvit" to ooze into the ply and make a solid epoxy base, then you can start thinking about re-caulking, and I would use a sealant that stays flexible, and do not overtighten. The co-efficient of linear expansion of the bronze is different to that of the glass/wood/epoxy and the joint must have enough thickness to be able to flex without tearing the seal from either part.
Make sure the holes through the boat are larger than the bolts, and fill the excess with sealant, this is why they used silly-cone originally the bolts must "float" in their holes.
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Old 31-08-2015, 20:34   #11
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Re: Butyl for sealing portlights and other questions?

Quote:
Originally Posted by sy_gilana View Post
You need to re-establish the plywood first. Look for "Git-Rot" and "Gluvit" to ooze into the ply and make a solid epoxy base, then you can start thinking about re-caulking, and I would use a sealant that stays flexible, and do not overtighten. The co-efficient of linear expansion of the bronze is different to that of the glass/wood/epoxy and the joint must have enough thickness to be able to flex without tearing the seal from either part.
Make sure the holes through the boat are larger than the bolts, and fill the excess with sealant, this is why they used silly-cone originally the bolts must "float" in their holes.
Pretty sure "Git Rot" won't be needed....

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A picture is worth a thousand words...

But...

At the bottom of each knee (where the chainplates bolt) the plywood is mush thanks to water having no where to go when it leaked in (or someone left the windows open). Plan is to cut away one side of the knee, dig out the mush and fill with thickened epoxy as fortunately the original ply contributes two tenths of nothing to the structural integrity of the vessel at that point. Unfortunately however, two of the knees need to be cut open and the plywood replaced as they are mush from top to bottom. I'm guessing at this stage water has leaked from a padeye or the jib car into a foam cored stringer and drained into the insides of the affected knees over time, or maybe just that they soaked up more water than the others over the years. Further dissection will hopefully reveal all. All I can say is yet another case of why you should never never look behind anything when working on a boat unless you want to find a lot more jobs to do!!!
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Old 31-08-2015, 22:13   #12
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Re: Butyl for sealing portlights and other questions?

Butyl worked really well for sealing a port light in an over sized cut out that allowed barely any overlap. Lots of evidence of PO's using several types of caulk including the dreaded Sillycone with out success. R&R'd the port with butyl tape and no more leaks after 5 years and thousands of miles. Fortunately it was all glass so no rot issues with the previous unsolved leaking.

The round ports on our old boat had the flange on the inside with a trim ring outside that we sealed with LifeCaulk (polysulfide). Still no leaks after 40 years.
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Old 01-09-2015, 09:21   #13
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Re: Butyl for sealing portlights and other questions?

I used butyl on two of my ports and have been chasing "grease" stains ever since. More than likely I used too much. There's a lesson here somewhere...
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Old 01-09-2015, 09:23   #14
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Re: Butyl for sealing portlights and other questions?

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I'm a big fan of Butyl and the PBase articles. I actually redid my portlights and bedded them with 5200 but in hindsight after finding out about butyl tape would have preferred to use butyl. My portlights on a 1981 Cheoy Lee 41 bed from the inside and have wood trim on the outside. To keep rain out I had to seal around the trim with 3M UV 4000 since it's exposed to light.

When you go to install and use butyl you make sure that the butyl goes all over the inside where the hull meets the portlight and through the cutout area. The best thing about the butyl is that it is WAY easier to remove than 3M 5200 or 4000 and provides a better seal as the hull flexes.
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Old 01-09-2015, 10:29   #15
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Re: Butyl for sealing portlights and other questions?

For the life of me I can't picture a portlight that only seals to the inside paneling. If water can get around the outside trim ring it will get behind the fiberglass and go somewhere else. Perhaps I misread something. If what I am thinking is true, I don't see how it could ever seal 100%.

But having expressed my ignorance, I love butyl tape. I have no experience with bad butyl so can't speak to that. But is it soft and I would want to have a good compression to keep it in place. It is soft and doesn't firm up like caulking. Which is one of its advantages normally.

I would never use 5200 for this as some have done in the past. Other sealants could be used as well - like 4200 or Sikaflex but I would still want as tight a fit as possible.

Good luck with your project.
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