Window sealant

[Gordonmc]

Have just stripped, sanded and sealed (Deks Oijlie) the mahogany of my saloon. The deadlights which screw directly onto the wood with no frame were shot, so I have fabricated new out of 5mm polycarbonate.
I am looking for tips on what sort of mastic/sealant to use on the mating surfaces. I know silicone is out, but I dont want to have excess gunk all over my pristine woodwork... or new windows. Something with the consistency of bluetack would be ideal for application.
Ideas gratefully received.

 

[vyv_cox]

For polycarbonate I would say silicone is your only choice. Any solvent-based sealant will cause cracking in short order. Make sure there is ample clearance around fixing screws.

 

[Guest]

Can you get your hands on some fast setting 3M 4200? It's one possibility.

Also if you have access to Boatlife products, you might want to try one of theirs that has a mixture of silicone and other sealants in it. I am anti-silicone on boats, but I also know that polysulfides can melt certain plastic materials. Not sure about polycarbonates though. If you check and find that a polysulfide will work without damaging the polycarbonate...use it....its the best for the job.

 

[vyv_cox]

I can assure you from bitter experience that polysulphides cause stress corrosion cracking in polycarbonate. It's best to avoid solvent-based adhesives on polycarbonate altogether. A great deal of work was done on this topic about ten years ago in regard to putting stickers on motorcycle crash helmets. Even the very small amount of solvent in a sticker adhesive was found to be enough to cause cracking.

 

[Boathook]

I am replacing the perspex in a deck hatch at present. The UK agent / suppliers sent 3M silicone 3200? and a primer for the perspex. This sits in an aluminium frame. The original was done the same way and lasted for over 20 years.

 

[Guest]

vyv_cox.....Thanks for the information. I was unaware of the effect of polysulfides on polycarbonates. I know know not to use the stuff when I replace the portlites on my boat.

I have never seen 3M's 3200 Silicone.....and I work for BoatUS!! I'll have to look that up and see what I can find out about it.
Biggest problem we run into is that people over here go to a hardware store and buy silicones that are for home use and use them on their boats....hence they have many residual problems.

Just goes to show that an "old dog can learn new tricks"!! Thanks again.