Frameless Windows

[James W]

The huge windows in the cabin roof of my boat leak there's no tomorrow. It's a common fault with the model (Jeanneau Voyage 12.5) and a number of owners have replaced without the aluminium frames, just sealing new plexiglass on with primer and then UV resistant Sika.

Andy from Boatworks Today uses a different method which looks much easier, utilising 3M VHB tape:

Has anyone done this? What are the thoughts about the efficacy and safety? It's no different to a car windscreen after all!

 

[Talulah]

I’ve used 3M VHB tape but not for Windows. A lot of window issues are where too much sealant is squeezed out when fitting the window leaving just a thin film. The VHB tape prevents this from happening.
On older windows with no VHB tape I have been able to push out the Perspex where the bond between the sealant and Perspex has broken down.

 

[Paulg25]

Good info ?

 

[Rappey]

It's no different to a car windscreen after all!

A windscreen is glass and sealants bond to it 100% (using the correct one)
Acrylic or similar is tricky to get adhesion.
Double glazing industry has been using double sided pvc foam tape for at least 25 years to bond in sealed double glazed units.
I don't use anything else to seal windows, hatches, deck fittings etc.
The tape is sprayed with soapy water to allow alignment before it starts bonding.
Sikaflex does not stick to polycarbonate very well even with primer plus it's an adhesive, not a silicon. Silicon is a sealant with flexibility allowing for the large amount of contraction and expansion with boat windows but without screws may not be strong enough on its own.
I removed some acrylic windows that were bonded and screwed with sikaflex where some of them had been very well abraded where the sikaflex made contact.
The sikaflex came off much easier on the abraded surfaces!
Bonding with tape is immensely strong. The guy in the video does seem to struggle with what silicon and caulk is, they are not the same.
There are specialised silicon for polycarbonate/acrylics (google) and I agree Dow sealants are very good.
Lastly how sealants are used is very important. Take teak decking. The bottom of the groove has to have a non stick strip so the sealant is just bonded to the sides allowing contract/expansion.
Don't use the tape and it will split down one side.
Now take a right angled internal corner and sealing it. Do what we all do and fill with sealant.
Now we have two adjoining planes and no seperation in the middle and over time it comes away one side.
Put a small non stick strip in the corner then seal over it and it will stay stuck !
Siliconing around the tape bonded boat window, a small non stick tape where the acrylic touched the grp, then seal over and it should never split, providing a proper polycarbonate silicon is used !