Alternatives to silicone – butyl...or something else?

[BabaYaga]

I would be grateful for some advice on a suitable window sealant.
In a few months time I will face the task of rebedding the windows on my mahogany coachroof sides, after having put on 8 – 10 coats of varnish from bare wood.
The construction is as shown in the cross section sketch below. The sealant should fill the space marked in red.
The sealant used originally was clear marine silicone, this is also the stuff that the knowledgeable people at the Vindö yard use today after revarnishing jobs.
Still I am keen to find out if there are any alternatives, mainly because silicone dust and varnish is not really a happy combination (this surface will be lightly abraded and re-coated every season).
I have been thinking about using a butyl-based sealant instead, possibly in the form of a thin tape to act as a gasket between the frame and the substrate.
Does this sound like a good idea? I am a bit worried that the modest wood screws might not provide sufficient compression, but at the same time too much compression could perhaps cause the sealant to squeeze out? It would be interesting to hear from people with experience of butyl what they think.
Sealants such as Sikaflex 291 and other poly urethan type are out, as they are 'too effective' and would make it impossible to remove the windows in one piece in the future. But maybe there are other types of sealants that I am not aware of, which might be suitable?

 

[Malabarista]

Wow beautiful job

 

[PabloPicasso]

I've used butyl tape to seal windows, and deck fittings. I've found it works rather well. Nice job of the varnishing mate.

 

[graham]

I recently helped a friend refit a window in a GRP boat with aluminium alloy frames and screws. We used butyl sealant strip which came in a roll with a paper backing strip. Job was succesfull the butyl was quite firm on a cold day we had to progressively tighten the screws leave for 15 minutes then tighten again bit at a time .I don't think you need worry about squeezing it all out.

Plus points were virtually no mess .The excess sealant coming out was trimmed off with a pen knife blade taking care not to touch the gelcoat.
Completely waterproof now.

 

[lw395]

Polyurethane sealant. What people usually mean when they say 'Sikaflex'.
Your sketch is good, because the sealing around the screws,in the groove between the wood and the glass is not being squeezed to zero, so it has a chance of moving with expansion etc.
You could fill the groove with sealant, and put rubber tape under the metal frame. That would avoid gluing the frame to the wood irremovably.
The joint is, IMHO, well designed and would work well with silicone, a low modulus silicone might be a good choice, but I appreciate there are reasons for not want silicone where you will be wanting to touch up varnish.

 

[LoneHort]

Hi BabaYaga, Get yourself some Scapa 3507 bedding tape , Hadlow marine is one supplier. It's available in 17mm and will work perfectly for your windows just like it did for mine. Once compressed 30% it's tight and your screws will do that and there is no mess compared to the butyl.

 

[alahol2]

Butyl tape, no mess, completely watertight windows. No question.

 

[vyv_cox]

Just a point of information. My windows were bedded on Sikaflex for many years. All of them were removed at least once, sometimes more and rebedded again on Sikaflex. They were certainly not immovable.

(The reason for constant removal was my attempts at sealing the glass to the frames. Subsequently I found that the wrong size glass had been fitted when the boat was built. Since replacing it no leaks for five years or more.)

 

[peteK]

I used butyl tape on windows easy to work with and have since used it on deck fittings with no leaks.

 

[Quandary]

I am in process of replacing all the fixed arylic on my boat, got some quotes and while Hadlow Marine were not quite the cheapest their price was competitive and they will sell you everything you need. They have an excellent website and are free with advice if you DIY. The Lewmar alloy framed windows with the acrylic set in to the channels with neoprene beads will be centred in the channels with acrylic spacers (the coachroof is slightly convex) and glazed in using Arbosil 1096, when set and cleaned up after all masking tape comes off they will be bedded to the coachroof using 12mm Scapa bedding tape. I will probably run a bead of sealant around the inside, 'just in case'. For the deck hatches Hadlow recommend EHB1203 hi-bond tape with Arbosil 1081 sealant. Hadlow recommend Greygate polish to extend resistance to crazing and 'Detak' for removing old sealant. This is how they do it and they should know.
The kit for 2 Lewmar framed windows, four Lewmar size 1 portlights and two Lewmar Ocean deck hatches, one with a hole for a vent in tinted acrylic with bedding tapes, sealants, packing pieces, frame joint spacers, new rubber rings , Detak and polish is just over 400 plus carriage, there is no vat.

Apologies, I got carried awaywith my own project and the OPs is quite different, Scapa tape (which I have not used yet) as recommended above from Hadlow marine is all you should need. Don't be tempted by adhesive sealants unless you are sure they will never ever come out again. Took me several days to get old silicone completely off each frame.

 

[BabaYaga]

Thanks all for your advice, so far. Although sometimes conflicting, as always, much appreciated.

One possible alternative that has crossed my mind is polysylphide. It would be interesting to hear if anyone has used this in an application similar to mine:
Arbokol 1000 - ARBO

Or perhaps MS polymer? The range of sealant types is truly bewildering.
MS Polymer Sealant Archives - Vital Technical

 

[Rappey]

I have worked many years in the double glazing industry and had many leaky boats out of wood etc and have probably tried every sealing method known to man.
Sealing windows with virtually any tube sealant/adhesive nearly always fails.
If you can peel dried sealant off the surface then it's not sticking. If you need a blade to get it off then it sticks.
Out of all the sealants I would say butyl is better than silicone, polysulphates, Ms polymers etc. Frame sealants that don't set tend to dry out over time and crack.
If you use butyl you should countersink the screw hole in the deck/cabin side as it holds the butyl and when tightened it forces the butyl up and down the screw thread.
Sikaflex is more of an adhesive whereas silicon is a sealant so silicon is better for trying to seal around a window to stop a leak but still fails after time as there is a way you are meant to use silicon and most the time it's not being used correctly.
Imagine a 90 degree internal (outside) corner and you want to put a line of sealant along it. Give it up to a year and one side becomes unstuck.
Now put a non stick strip in the corner and seal over it. The sealant is now stuck both sides with nothing stuck in the centre. Now the sealant will not peel off and last a very long time. Wooden decks, fill up the groove and it will peel off one side but put the non stick strip in the groove, sealant is then just stuck to wood either side and it can expand/ contract and will not split. Basically sealing with 2 planes touching can result in failure but seperating each sealed surface is the correct way to use sealants. I hope that makes sense as that's a little difficult to explain.
Now to what I only use as it never fails and is so easy to do - double sided glazing security tape. It's a pvc foam tape. Easy to put on and when the screws are tightened the foam gets squashed around the screws stopping any water.
Cover the tape with soapy water for positioning as one it touches it instantly sticks, soapy water allows for positioning.

 

[[176172]]

I would be grateful for some advice on a suitable window sealant.
In a few months time I will face the task of rebedding the windows on my mahogany coachroof sides, after having put on 8 – 10 coats of varnish from bare wood.
The construction is as shown in the cross section sketch below. The sealant should fill the space marked in red.
The sealant used originally was clear marine silicone, this is also the stuff that the knowledgeable people at the Vindö yard use today after revarnishing jobs.
Still I am keen to find out if there are any alternatives, mainly because silicone dust and varnish is not really a happy combination (this surface will be lightly abraded and re-coated every season).
I have been thinking about using a butyl-based sealant instead, possibly in the form of a thin tape to act as a gasket between the frame and the substrate.
Does this sound like a good idea? I am a bit worried that the modest wood screws might not provide sufficient compression, but at the same time too much compression could perhaps cause the sealant to squeeze out? It would be interesting to hear from people with experience of butyl what they think.
Sealants such as Sikaflex 291 and other poly urethan type are out, as they are 'too effective' and would make it impossible to remove the windows in one piece in the future. But maybe there are other types of sealants that I am not aware of, which might be suitable?

I would be grateful for some advice on a suitable window sealant.
In a few months time I will face the task of rebedding the windows on my mahogany coachroof sides, after having put on 8 – 10 coats of varnish from bare wood.
The construction is as shown in the cross section sketch below. The sealant should fill the space marked in red.
The sealant used originally was clear marine silicone, this is also the stuff that the knowledgeable people at the Vindö yard use today after revarnishing jobs.
Still I am keen to find out if there are any alternatives, mainly because silicone dust and varnish is not really a happy combination (this surface will be lightly abraded and re-coated every season).
I have been thinking about using a butyl-based sealant instead, possibly in the form of a thin tape to act as a gasket between the frame and the substrate.
Does this sound like a good idea? I am a bit worried that the modest wood screws might not provide sufficient compression, but at the same time too much compression could perhaps cause the sealant to squeeze out? It would be interesting to hear from people with experience of butyl what they think.
Sealants such as Sikaflex 291 and other poly urethan type are out, as they are 'too effective' and would make it impossible to remove the windows in one piece in the future. But maybe there are other types of sealants that I am not aware of, which might be suitable?

I rebuilt a number of windows in the past both fixed and opening. I contacted a marine window (their name escapes me) company who supplied me with a roll of neoprene type sealer, about an inch wide which was perfect, it turned the corners without to much trouble. Punched holes in it to suit, trimmed off the surplus. So much better I feel if they have to be taken out for any future reason.

 

[saxonpirate]

Its all been said really, but here's another for butyl tape, and that's backed by 40+years of Pro- yacht/boat construction experience. Whatever you do don't use the likes of sikaflex. You'll have to tear the boat apart if you ever need to remove the windows again.

 

[Slocumotion]

I've had difficulty with a construction like your original drawing . Screwing through the butyl tape winds it up around the thread, and punching a clearance hole through it first rather defeats the object of sealing around the screw - so you need a tiny rolled-out sliver of butyl wrapped around the countersunk head just before it's screwed home. Then you decide that through-bolting would have been better yet , despite introducing a hole right through to the interior, since you wouldn't then be dragging the butyl round and round in the gap but drawing it in. What about a combination then, of butyl tape with clearance holes , flat-headed through-bolts with a nylon washer and a touch of silicon round the threads? Nicely , progressively tightened up over a day or so and then maybe slackened off just a tad ? ( wouldn't want the glass bedded on any material racked to the very limit of it's compressibility would one?) Oh ,but then - what happens in that silicon-ed hole when you unwind the bolts after a day of setting up? - grease better?...
And so it goes - on and on...

 

[JumbleDuck]

How about polysulfide? In my experience it sticks to anything and stays flexible for ever. Whiffs a bit, though.

 

[Quandary]

There is a comprehensive definition of the qualities of all the different sealants here
boat-renovation.com/marine-sealants/
for instance, did you know that polyurethanes were incompatible with acrylics

 

[burgundyben]

I had windows of exactly the same type for 14 years.

Polyurethane sealants do too much damage when you need to take it apart.

I found polysulfide did not stick to the window.

I found glaziers linseed putty dried out.

My final attempt was a sucess. I used arbomast BR squeezed from a gun, but I lined the rear face of the window frame with Neoprene 3mm thick self adhesive foam tape. Screws punctured through the tape and compressed the foam tape.

(On mine, cabin side 5/8ths ply, the 330 odd screw holes were run out, I drilled them bigger and glued in plugs of teak, but they either crumbled or water wicked along them. Finally, I lined the cabin sides internally around the perimeter of the windows with 1" mahogany and used screws 1.25" long through the ply into the new Mahogany, the clamping force was much better, arbomast and the neoprene tape and it was perfect)

 

[Keith-i]

Arbomast BR or Butyl tape. I wouldn't use anything else now.

 

[PetiteFleur]

I'also used Butyl tape on windows and hull fittings, on the windows I fitted stainless washers between the window and grp so the butyl didn't get squeezed out too much. Worked for me, no leaks at all.