Bolted on windows.

VicS

VicS

Well-Known Member
Joined
13 Jul 2002
Messages
48,739
Visit site
If new windows are to be bolted on rather that fitted in rubber:

What sealant is suitable if a sealant is used. Will a clear silicone be OK or will it breakdown in UV light.

Tape is often suggested as being better than sealant. What is it and from where can it be obtained?

I know that screw holes must be a little over size to prevent the widows cracking but in the back of my mind there is some objection to countersunk screws causing the same problem. Is that correct?
 
I remember seeing a Rival Bowman 48 at a Boat Show with very attractive and elegant windows - and not a mechanical fastener in sight!
The windows were simply bonded in place with the most adhesive type of Sikaflex - many folk commented on this at the time, but we were reassured that the bonded joint was massively strong.

I can subscribe to this approach - I have tried to remove fittings bedded down on 5200 (American equivalent of the most sticky Sikaflex) and they were a right sod. I am not looking forward to the time when we eventually will have to remove the keel shoe supporting the base of the rudder on our Challenger - I lavishly stuck it on with 5200 10 years ago, and in retrospect, I should have just used ordinary sealant, as it also has 2 x 10 mm bolts through the keel holding it on.
But I digress.....
One could argue that if you are using a powerful adhesive, then the additional screws or bolts (if employed) are simply just another source of potential leaks.
 
(1) Silicone RTV elastomer will not break down in UV light. In the 1970s Dow Corning stretch tested RTV elastomers in Death Valley USA. After 20 years the test pieces were still in good condition.
If sealing non metal to non metal, it should be OK to use an acetic acid curing RTV. Use the non-acid curing RTV if sealing against metal. I would anyway first coat the metal with epoxy before applying silicone RTV.
(2) If you can source tape made from EPDM rubber, it, like silicone, is long term (20 years plus) UV resistant
(3) If the window pane is made from acrylic, it will be prone to stress cracking. Polycarbonate is less prone but can still crack. Also if using polycarbonate, do not rely only on adhesive because polycarbonate has non-stick properties. Whenever drilling sawing or shaping, follow the manufacturer's advice for stress relieving cut edges. When fastening, have a good measure of elastomer between the hole edge and the metal screw. This can be RTV sealant or O rings cut from heavy wall EPDM tube.
(4) Same applies for countersunk screws. Avoid screwing directly against the panel. Use an elastomeric material as a gasket to prevent the screw point loading against the plastic.
 
Hi Vic
I am fitting aluminium fromed windows to my new yacht using foam rubber as the sealant

On my previous yacht I fitted poly carb windows direct to wood frames and the wood frames glued in with sikaflex.

If rgw windows are bolted direct to the hull/cabin side using countersunk screws with the head countersunk into the window and not a frame covering it the holes in the cabin side need to be much bigger than the screws to allow expansion. If the wibdow is fitted between the cabin side and a al /ss /wood outer frame the clearance hole must be in the window materal.

I have used heavy duty foam rubber on all my windows and not had a leek yet.
 
[ QUOTE ]
Tape is often suggested as being better than sealant. What is it and from where can it be obtained?

[/ QUOTE ]

I used neoprene tape from ASAP 3-4 years ago (Also available from ARCO - cheaper, wider range of widths, but high P&P if you don't collect) and pan head stainless self-tappers from Screwfix.

I did get a small leak last year which I traced to the tape settling slightly - cured by tweaking up the fixing screws, which were all very loose.

I would do it the same way again - I hate to think of the mess I would have made with sikkaflex, etc.

Andy
 
Don't use a solvent based adhesive with polycarbonate windows. It causes stress corrosion cracking around the screw holes. Apparently this problem was once a big issue with motorcycle helmets when people put adhesive stickers on them and they subsequently cracked. I didn't know this, learned it the hard way and had to buy a complete new set of windows.

Sika do a special sealant for polycarbonate panels, details were on their website and I assume they still are. Otherwise, silicone is OK as it contains no solvent. I find clear silicone to be still OK after two Mediterranean seasons although I have read that it will break down there.

Pan head screws are normally used as the radial force applied when driving home countersunk screws may induce cracking.
 
Old Widows often crack up I find! /forums/images/graemlins/laugh.gif
But to be serious, you need to use Sikaflex 295UV. NOT the 291 generally available. Even then it is advisable to use protection tape over the top to stop direct UV light getting in. Clear Silicone is useless.
I would suggest you find your local Sika rep and ask him for a copy of a superb leaflet that they publish called "Bonded transparency for a clear view" Tells you exactly how to do it. The common fault is not using the appropriate primers and not having the joint thick enough. In fact if you do it according to their instructions you wont even need to drill the window for bolts! (Usually horrifies people until you ask them how their car windscreen is held in place!)
 
Hi Vic,

Slightly off-topic, but may be helpful...

I read an article some time ago that highlighted the possibility of leaks developing as a result of the sealant being squeezed out from between the window and the cabin side when the screws were tightened. The solution advocated was to fit plastic spacers onto the screws between the window and cabin side. These maintain a constant gap between the window and cabin side, which the sealant then fills, and the sealant won't get squeezed out as the screws are tightened.

Hope this helps,
 
[ QUOTE ]
Old Widows often crack up I find

[/ QUOTE ] I might have known some wag would spot that typo. I saw it in the preview but could not be bothered to correct it!

Thanks for all the replies though. The questions arose from a question I was asked while wearing my Technical Advisor to the SWOA hat. I will refer the questioner to the whole thread I think
 
I have just done this same job on a friend's Virgo Voyager, and had advice from the Virgo Owners Association (For which grateful thanks). The tape you are seeking is called Bear Tape and can be obtained from Aladdin's Cave chandlery. It comes in 2 widths. 50mm at £2 per metre, or 25mm at £1 per metre. It is a grey closed cell foam, about 3mm thick, self adhesive on one side and is very easy to use. I was advised that this was the original method of sealing the windows when the Virgos were built, and lasted for many years. The tape then became 'unavailable' so sealant was used by owners but this failed quite quickly. Feel free to PM me if you need any more info.
 
Vic..When I did this on my last boat I over sized the bolt holes and used pan heads..also painted the inside of the perspex/acrylic around the edge with black paint ( or as appropriate) to cover the sealant.

For definate use tape..I get it from Aladins cave but Im sure the chaps at Seateach must have it..

Regds Nick
 
Registering No Commercial Interest - Just great Customer Experiences.

Trust me when I say I feel your pain.

I was hesitant about carryign out the work myself but foudn it very reewarding and now, very dry, below /forums/images/graemlins/blush.gif)


I bolted on with did this using 3mm neoprene sheeting from Seals Direct

Acrylic holes should be 1mm larger than bolts or screws.

I used pan head bolts with interscrews for lovely finish on the inside. Sea SCrew best prices I found.

Steve at Talking Plastics has been doing this for years and provides the windows. Heluva guy - great service & 20 yrs experience of fitting/advising these kind of windows.

Took 3 days to prepare surfaces (infernal Sikaflex) & 2 days to fit - including drilling 200 holes and a beer for lunch.
 
I did mine last year and used 3 x 25 mm closed cell foam tape. Fixed with pan head screws which had rubber washers under the heads. Don't over tighten the screws on reassembly. I left a gap of about 3mm from the edge of the tape to the outside edge of the window. This gap was then filled with silicon sealant and looks very neat. All leaks gone.
 
You must log in or register to reply here.

Share this page

Top