Gunk of choice for window sealing

[Kelpie]

My old Moody has aluminium window frames, I think they're a pretty common design- outer part, middle, inner. The middle section has a U-channel about 15mm wide, the perspex sits in this needed in some sort of sealant.

For sealing the outer part to the cabin top, no question, butyl tape.

But for the channel section, is there something better? I've done one window using the butyl and whilst it worked, it was a real faff and took me the best part of a day, slowly forcing the stuff down into the gap. Weapon of choice turned out to be half a moist clothespeg, so I was working about half an inch at a time.

Is there some kind of gun applied non setting gunk that I could use for the remaining windows?

 

[roaringgirl]

I'd use butyl tape, everything else I've used over the years has failed after a season due to movement.

 

[dankilb]

Arbomast BR - ARBO
Non setting butyl sealant (not tape) for the channel itself…

(And before anyone else says it - definitely not CT1, OB1 or Sika!)

 

[AndrewB]

Arbomast BR - ARBO
Non setting butyl sealant (not tape) for the channel itself…

(And before anyone else says it - definitely not CT1, OB1 or Sika!)

Well, I'm saying it. Six years ago I re-bedded the leaky aluminium windows on my Moody with Sika 295UV, no problems since.

 

[dankilb]

Well, I'm saying it. Six years ago I re-bedded the leaky aluminium windows on my Moody with Sika 295UV, no problems since.

The UV - yes, fair enough.

It’s an expensive option, mind. And what’s the plan for future removal without damaging the frames?

 

[Bobc]

Butyl. Nothing else.

Either use butyl tape, or buy ABROMAST BR (butyl in a tube).

 

[Tamar]

I got some stuff from Toolstation butyl roofing stuff. Can't think of the name but it stays soft. It's a long job to do it properly, it took me almost a week to do two windows, hardest part is getting the old stuff out and cleaning everything up. Two years down the line and one window has just started to leak slightly, so I couldn't have done it properly. It's not a job I want to do again.

 

[AndrewB]

The UV - yes, fair enough.

It’s an expensive option, mind. And what’s the plan for future removal without damaging the frames?

Sika 295UV is partly adhesive, but not all that strong (rated at 2MPa). It needs care, but in the past I've successfully broken out Sika bedded fittings without damage. However, I'm hoping I'll never need to!

 

[Keith-i]

If it’s plastic into a frame with only some thermal movement to worry about then I’d use a proprietary glazing sealant from Dow Corning. They are specifically designed for this type of application. I rebedded the acrylic panel in my roof hatch a few years ago and it has been fine. I’ll dig out the product number later.

 

[vyv_cox]

My windows were rebedded professionally in Athens. They used a cured silicone and use the same for all types of window, including underwater ones on a particular catamaran.

 

[geem]

The OP is in the Tropics. We have found thatt butyl is not a great solution out here. It doesn't seem to cope well with the UV and heat. It turn liquid after a while and simply runs out, especially if under any sort of compression. You can buy the correct grade of Sika for windows in Budget marine here but I forget which one. There is also a special primer that goes with it for perspex

 

[Kelpie]

The OP is in the Tropics. We have found thatt butyl is not a great solution out here. It doesn't seem to cope well with the UV and heat. It turn liquid after a while and simply runs out, especially if under any sort of compression. You can buy the correct grade of Sika for windows in Budget marine here but I forget which one. There is also a special primer that goes with it for perspex

Will I be able to get them apart again, though?
We may only be in the tropics one more season. Planning to head north after that.

 

[Keith-i]

Dow Corning Structural glazing sealant 895 is the stuff I used (and you need). It's a neutral cure silicone and can be removed with a knife if needed.

 

[Poignard]

Arbomast BR - ARBO
Non setting butyl sealant (not tape) for the channel itself…

(And before anyone else says it - definitely not CT1, OB1 or Sika!)

If you don't think CT1, OB1 and Sika are suitable, can you please say why?

 

[dankilb]

If you don't think CT1, OB1 and Sika are suitable, can you please say why?

They degrade with UV. Well documented/known. Fine with most deck fittings, but glazing is more demanding - thus the availability of specialist glazing sealants (typically structural silicone or specialist PU formulations like Sike295UV cited above).

Another reason I don’t think it’s helpful to suggest adhesive sealants is the OP already indicated a (very sensible!) desire to use butyl - a non curing sealant.

 

[Kelpie]

If you don't think CT1, OB1 and Sika are suitable, can you please say why?

Getting the outer frame off the side of the cabin top without resorting to chisels and pry bars, and without bending the frame.
Getting the perspex out of the channel- there's a lot of surface area and no way to lever it out.

 

[dankilb]

Dow Corning Structural glazing sealant 895 is the stuff I used (and you need). It's a neutral cure silicone and can be removed with a knife if needed.

It’s great stuff (I hope - it’s holding all of our ‘windows’ in aside from opening port lights/hatches). However, I’m not sure removing it from a framed window would be so trivial. I had to remove a 10mm strip from a couple of (unframed) acrylic windows I’d fitted and not left enough expansion gap. The 895 was stuck like nobody’s business (good for the rest of the windows!). It took good prying off/hacking out. It had bonded well enough to remove some gel from grp!

 

[dankilb]

OTOH with Dow 895 and Sika 295UV I do concede there’s a good chance of not needing to worry about the bond in your ownership of the boat. Horses for courses…!

 

[thinwater]

If you don't think CT1, OB1 and Sika are suitable, can you please say why?

Specifically, the UV goes through the glazing and attacks the bond. I've done testing, and if the uv strikes the underside, polyurethanes let go within 2 years, even Sika (which is why they use an opaque primer).

Dow 795 in the US and Dow 895 in the UK. If you look at buildings with glass exteriors, this is what they use.

Not hard to remove with the correct remover (Marine Debond).

 

[Poignard]

But what if the sealant is not exposed to UV, because it is hidden behind a s/s bezel, for example?