New perspex windows- Sealant or Butyl?

[pompeydave]

Hi all, I've got a Trapper TS240 for which I'm having new 6mm perspex windows made. My dilemma is the refitting. Each window is held onto the side of the coachroof by about 20 stainless screws and it looks like there was originally some sort of white Sikaflex type sealant on there originally just as a seal, but not as an adhesive. The windows are being replaced due to cracking at each screwpoint but they mount flat and the perspex isn't under any stress accordingly.

Would a thick bead of Butyl give a more flexible mounting to prevent future cracking of the new windows, or am I better off using another sealant as before? Any makes of sealant/butyl that are better than others?

Thanks in advance.

 

[stuartwineberg]

I understand that butyl mastic or butyl bead tape is the way to go. Very flexible, never hardens and allows removal later if required

 

[Aja]

The cracking experienced at each screwhole is due to the stainless screws expanding at a different rate from the acrylic. Advise you make the holes in the acrylic one size larger or you'll get the same result.

+1 for the butyl tape

Regards
Donald

 

[PetiteFleur]

Butyl tape is the answer - as used on fitting double glazed glass to wooden frames. Try not to use countersunk screws, use shallow round head screws if you can. Also fit a small stainless washer between the Perspex and the boat and the butyl tape won't all squeeze out when the screws are tightened. Start from the centre of the Perspex and work evenly towards the ends.

 

[michael_w]

I had endless problems with leaky windows till I bit the bullet and re bedded them using the right stuff from Sika. http://www.sika.com/en/solutions_pr...arine-market/marine/leisure-boats-yachts.html

Not cheap, but it works. The main problem is maintaing an adequete bond whilst allowing for the vastly different thermal expansion rates of acrylic, GRP and aluminum.

 

[ghostlymoron]

I must disagree about sika. In the OPs situation, adhesive qualities are not required. The perspex is held in place by the screws, and the water is excluded by the sealant. I'd use butyl tape.

 

[alahol2]

My take... http://www.troppo.co.uk/odds/Flying%20Fox%20Windows.pdf

Now 5 seasons in and no leaks nor splits in the acrylic.

 

[Javelin]

If you have confidence in the fixings then no need for sika.
I would use Arbokol 1000 which is similar to butyl but performs better over time, is more flexible and is easier to pull the perspex up to the grp.

 

[BobnLesley]

+1 for Butyl Tape, but don't sail too far south: I rebedded a 'problem' window and then the rest using Butyl tape a couple of years ago following recommendations on this forum.

It was brilliant stuff, up until wereturned to the tropics, where it quite quickly softened and 'began to run' on the port-side windows (presumably the 'sunnier' side?) to the extent that it soon began to leak. At least it was easy to get off again.

 

[AndrewL]

Have you considered self adhesive closed cell foam tape? I replaced my windows 3 years ago using it and have had no problems at all. Sticky side against the coachroof to avoid UV damage to the adhesive. From memory I used 20mm tape. It gives a neat looking black border to the window and allows for expansion.

It's been discussed here before
http://www.ybw.com/forums/showthrea...neoprene-sheeting-for-bedding-perspex-windows

 

[TSB240]

I had a trapper Ts 240........

I used Butyl tape and self tappers. (The inside of the screw points are covered by a bonded capping so you don't have the option of using bolts and nuts. If using self tappers you may find you need to go up a size as the fiberglass shell is thin and is the only thing retaining the widow. There is no backing pad. If going up a size make sure the screw holes in the window are clearance to allow for expansion and flexing of the coach roof. Yes.It flexes especially if you apply the recommended 3/4 rig tension!

Once done we had a dry boat for three years!

Miss that boat terrific 24 footer that would sail the pants off my new boat!

Top tip If you are getting unexpected amounts of water in the bilges after burying the nose into a big sea check that the top of the anchor locker is sealed! Ours overflowed due to Trappers missing out a bit of sealant at the back and we only noticed this when the carpets started floating. Sailed even better with 250 litres of water ballast!

 

[paulg567]

I have T300, similar window setup to yours

Replaced my windows last year, made them myself and installed using tape to seal. Far less mess than sealant!
When fitting, make sure you start installing the screws in the middle of the window and then work your way outwards.
Don't over tighten the screws and you will be fine.

Several hundred miles later, in some very rough conditions I've not had a single leak and they still look like new.

I concur, the Trappers sail beautifully.

Cheers!

 

[pompeydave]

Thanks for all the advice everyone, I'm going to get some butyl tape.

 

[ianj99]

Hi all, I've got a Trapper TS240 for which I'm having new 6mm perspex windows made. My dilemma is the refitting. Each window is held onto the side of the coachroof by about 20 stainless screws and it looks like there was originally some sort of white Sikaflex type sealant on there originally just as a seal, but not as an adhesive. The windows are being replaced due to cracking at each screwpoint but they mount flat and the perspex isn't under any stress accordingly.

Would a thick bead of Butyl give a more flexible mounting to prevent future cracking of the new windows, or am I better off using another sealant as before? Any makes of sealant/butyl that are better than others?

Thanks in advance.

Use caravan mastic. I used it when refitting the windows to my steel ketch and no leaks after 7years. It is none setting and surplus is easily removed with white spirit.