sealing troublesome windows! best mastic ..?

[TactilePaul]

We have had persistantly leaking windows in our Grand Soliel 343, I have refit the worst of them twice, the problem seems to be a discrepency between the curve of the window and boat!, when screwing on, the Abromast mastic used gets squeezed too much upon installation as forces are greater in some areas due to 'wrong curve', either this or expansion is affecting the seal? also the screws are not really grabbing anymore, I am not sure of that grey sticky mess!?, it never sets and seems to crack?
I am of the opinion that the next step is to go for something more permenant, when set, the screws will mostly be decrative and a nice white finish would be a bonus!
Can someone recommend a mastic that they would use?, we have teak off and interior is a mess, it the perfect time, my gut feeling is to use plenty of quality sikaflex ...something???, and mask the hell out of surrounding area!! Its something that absolutely needs doing correctly first time! , I am a plumber, so should have the skills, but i am still apprehensive!
Thanks

 

[johnalison]

I'm no expert but I'll start the ball rolling by saying that a year ago I had to replace an errant windscreen panel. I used a silicone-rubber-compound, not Dow-Corning which was recommended but something the chandler happened to have. It sets as a rubber and from my experience stuck like hell, judging by the difficulty of removing the excess. It was necessary to clean well first with acetone.

 

[Rappey]

If you can squirt some tubed sealant onto what I would guess is acrylic then peel it off when set then it's not the right sealant for the job.
There are not many that will permanently adhere to polycarb/acrylic .
Upvc foam tape is the way to go. No mess and once done will never leak.
I would say the biggest problem is the huge expansion and contraction of the window compared to the surround it's sealed to.
Sikaflex very rarely last, plus most of it is an adhesive, not a sealant.

 

[john0740]

Upvc foam tape is the way to go. No mess and once done will never leak.

That's my experience also. I have found success with tapes from this range. (Only connection is as a customer).

 

[Bobc]

You might find that butyl tape works better than Abromast. At least it won't get "squeezed out" like the gob does.

If you really want to glue them in permanently (I wouldn't recommend it though), then CT1 is the thing to use (not the clear one).

 

[TactilePaul]

That's my experience also. I have found success with tapes from this range. (Only connection is as a customer).

thanks, I like the look of this 'mess free' method!, the curve will need to be forced into line if i chose it though,, hopefully screw holes can be repaired in order to achieve this!

 

[Blueboatman]

I have never had a leak after rebedding in Sikaflex- not a near substitute or a value substitute but actual expensive sika. Do remember , sikaflex evolved from bonding glass windscreens to metal car frames and that process seems to cope well with the earths temperature disparities and operating conditions , no?
However ... this is just my personal experience .

Where the curve of the window fails to follow that of the grp or alloy frame , try a dry run using a couple of humble match sticks as a spacer to see if that sets the right space all around ? If so , match sticks prevent the sealant being disproportionately squeezed out as you bed ( or force!) the glass down .
I have successfully in the past removed all the aging, hardened, shrinking rubber inserts from alloy/glass windows and using ( match stick ) spacers each side of the glass , bedded the whole lot together and also to the grp using sikaflex ..( the more carefully you mask off, the easier the clean up .
Once set you remove the 2,4 or8 match sticks and dab-fill with a dash more sika
So if you want quick cheap and easy , don’t do this
But , done right , sorted ?
It is not “ the best” or “the only” way of course , nothing is !
But ... I trust this method and material more than any other . And I do like dry windows on a boat , summer winter tropics or temperate zone.

 

[PlankWalker]

If you use Sikaflex, it may well solve the leak,
but you wont get the windows off again without considerable damage.

 

[Keith 66]

This^^^^^^ Sikaflex is all very well until the day you have to get the window out. Then you will most likely rip the gelcoat off in chunks.

 

[TernVI]

Most sealants have a figure of how much they can be stretched.
Often a percentage. 100% is not uncommon.
If the sealant is squeezed to zero thickness, it has zero to give before tearing off one surface.
Mastics which don't set can be moved around, but leaks will happen when they move so much that a gap is left.

The trick is to design the joint so that the sealing happens in a decent thickness of sealant. If you've got a 2mm bead of sealant, it will probably accommodate 1mm of movement before failing, if it sticks to both surfaces OK.
Very often you can improve things a lot by either making a groove for the bead of sealant to sit in, or spacing the window away from the GRP. Then you need a sealant that sticks and a clean joint.
I found spacing the windows away from the GRP on a rubber tape gasket, leaving a joint full of silicone snot did the trick.
Lower modulus snot moves more creating less stress trying to tear the sealant off the surfaces. Polyurethane is better, stronger snot, but you may need a deeper bead to allow for the same movement.

 

[TernVI]

This^^^^^^ Sikaflex is all very well until the day you have to get the window out. Then you will most likely rip the gelcoat off in chunks.

It's good to have a joint where you can run a scalpel around the sealant.
I once 'temporarily' fitted something with common silicone bathroom snot, it resisted hundreds of kg of trying to pull it off, I had to make a tool to attack the sealant!

 

[ghostlymoron]

On windows with aluminium frames, I used PU40 (from Toolstation) to seal the glass into the frame, and butyl rubber tape (from a caravan dealer). No leaks so far

 

[rogerthebodger]

This^^^^^^ Sikaflex is all very well until the day you have to get the window out. Then you will most likely rip the gelcoat off in chunks.

This kind of knifes will easy cut and sealant without any damage to the window.

 

[MOBY2]

Just redoing mine at present, have put the glass back in the frames with sikaflex but was concerned using it or ct1 on the gel coat so have opted for butyl asafriend who fits windscreens for Rolls Royce said it would be a better way to go and to warm it with a hot air gun to get better adhesion ... will let you know how it goes...

 

[Deleted member 36384]

The Scapa Foam mentioned above, post No 4 is what I used. Do not use a sealant and certainly not an adhesive selant. I used the 3mm thick tape on the frames, some of which had to bend around a slight curve in the coachroof, about 7mm offset from the flat, over the frame length. Screw the frame down until you get a good bulge of foam on the corners, on the tightest corners I estimated that the frame was about 0.5 mm away from the coach roof. On the flats I squashed the tape about 2mm. It's over 5 years now and not a drop of water has entered the boat despite the wet West Coast of Scotland and some very heavy weather experiences. Simply put, it is the correct stuff for the job and if you have to remove the window again, no issues as the tape is a resilient seal i.e. it wants to reform to it's original shape. UV wise I have seen no deterioration where it has extruded.

Regarding your persistent leaks. I had this, despite death by sealant, turned out the frames had corroded through on the underside. The channel that the window sat in, U channel, clamped the frame between the a large O ring on the outside and sticky tape on the inside. The O ring was trash and water had been sitting in the U channel and had corroded a hole in the bottom of the frame. Hence, all the sealing of the frame in the world was not going to stop this. The refurbishment resulted in the glass being bonded in the U frame with Sikaflex which filled the frame completely i.e. the O ring and tape that originally held the glass in place was done away with. Hence, check the frames, as water may be leaking internally and not from the flange face of the frame / hull.

Frame and Foam Tape

Extruded Foam Tape After Fitting Window

Corrosion Holes In Frame Sealed With Sikaflex (Similar Holes Were On The Underside)

 

[captainboo]

The Scapa Foam mentioned above, post No 4 is what I used. Do not use a sealant and certainly not an adhesive selant. I used the 3mm thick tape on the frames, some of which had to bend around a slight curve in the coachroof, about 7mm offset from the flat, over the frame length. Screw the frame down until you get a good bulge of foam on the corners, on the tightest corners I estimated that the frame was about 0.5 mm away from the coach roof. On the flats I squashed the tape about 2mm. It's over 5 years now and not a drop of water has entered the boat despite the wet West Coast of Scotland and some very heavy weather experiences. Simply put, it is the correct stuff for the job and if you have to remove the window again, no issues as the tape is a resilient seal i.e. it wants to reform to it's original shape. UV wise I have seen no deterioration where it has extruded.

This is exactly the same as I did for my windows and also on the West Coast. Been in for 10 years with no leaks. Tape came from Hadlow Marine who also refurbished the windows. They were held in originally with sikaflex type sealant and were a pig to get out plus pulling chunks of gel coat off!

 

[TactilePaul]

If you use Sikaflex, it may well solve the leak,
but you wont get the windows off again without considerable damage.

why would this be any different to removing a car window?, plastic I guess?

 

[TactilePaul]

thanks for great answers everyone, again.., this forum is by far the most useful and accurate of all that I am a members of!, ! I think i am going to try combining all these methods, as i nice 'sika', fingered finish is going to be required I feel, but i shall be using tape also, and maybe matches to maintain the gap!!

 

[TactilePaul]

The Scapa Foam mentioned above, post No 4 is what I used. Do not use a sealant and certainly not an adhesive selant. I used the 3mm thick tape on the frames, some of which had to bend around a slight curve in the coachroof, about 7mm offset from the flat, over the frame length. Screw the frame down until you get a good bulge of foam on the corners, on the tightest corners I estimated that the frame was about 0.5 mm away from the coach roof. On the flats I squashed the tape about 2mm. It's over 5 years now and not a drop of water has entered the boat despite the wet West Coast of Scotland and some very heavy weather experiences. Simply put, it is the correct stuff for the job and if you have to remove the window again, no issues as the tape is a resilient seal i.e. it wants to reform to it's original shape. UV wise I have seen no deterioration where it has extruded.

Regarding your persistent leaks. I had this, despite death by sealant, turned out the frames had corroded through on the underside. The channel that the window sat in, U channel, clamped the frame between the a large O ring on the outside and sticky tape on the inside. The O ring was trash and water had been sitting in the U channel and had corroded a hole in the bottom of the frame. Hence, all the sealing of the frame in the world was not going to stop this. The refurbishment resulted in the glass being bonded in the U frame with Sikaflex which filled the frame completely i.e. the O ring and tape that originally held the glass in place was done away with. Hence, check the frames, as water may be leaking internally and not from the flange face of the frame / hull.

Frame and Foam Tape

Extruded Foam Tape After Fitting Window

Corrosion Holes In Frame Sealed With Sikaflex (Similar Holes Were On The Underside)

thanks, I really appreciate you taking time to help me, will definately look v carefuly at them!!

 

[ghostlymoron]

why would this be any different to removing a car window?, plastic I guess?

Car bodies are generally steel not fibreglass?