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Kennneee

Window/Port bedding

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Hi Guys- I am close to bedding the windshield  and ports on ROSIE.  The windshield is safety glass and the ports are Polycarbonate and acrylic.  I was going to use Sikaflex 291 but wonder if there is a better alternative.  Any suggestions or tips appreciated. I also have heard that some builders use copper tacks in the wooden windshield frames to support the glass.  Any elaboration on that would be helpful. THANKS.

Ken

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I have a little experiment going. I use this stuff on my house and it seems to work well.

 

https://www.homedepot.com/p/DAP-Alex-10-1-oz-Painter-s-All-Purpose-Acrylic-Latex-Caulk-18609/100078928

 

It cleans up with water and fills gaps nice. I laid a nice bead on some plastic scrap to see if there is any interaction. If none, this is what I'm going with. Cheap, UV resistant and cleans with water. And no silicone. All the other stuff I've looked at have solvents and seem to harm plastics.

 

Of course it will be years before I can tell you exactly how it worked out!

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For safety glass the Sikaflex is excellent.  For plastics nothing works like, (shudders) silicone.  It is what the manufacturers of polycarbonate and acrylic insist on.  Just be very careful and mask.  Once something has had silicone on it it becomes suspect for any future bonding of any kind.

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I personally etch my safety glass around the perimeter for a super bond. Make sure you paper the entire area that's not going to be etched, doubled up if the paper is thin. Use a quality tape for the etching stop.  Then tape the paper over the tape on the marked line for etching. Make your template for your glass with  small brads or tacks around the perimeter of the template for your glass . When setting the glass into the caulking, the small void will allow some of the caulk to seat between the perimeter of glass and the frame.  After the caulk cures remove the tacks and install the mouldings for the inside trim against the glass with a small amount of caulk. When figuring out where to etch the glass, set the glass with the tacks around the perimeter and mark the glass with a sharpie for the tape job. There is a chemical for etching available even at most hobby stores. But ask your glass shop too if they have it.  Wear gloves and eye protection for sure.

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Hirilonde- Which Sika do you recommend? I have a lot of 291 in the shop and wonder if that is a good choice for glass.?

Ken

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All Sikaflex products are polyurethane.  The differences are tensile strength and curing time.  I use Sikaflex 291 fast cure.  It has a tensile strength of 300 psi which is about half way to 3M 5200.  It makes a strong bond, but still reasonable to take apart down the road.

A technique I use for all bonding is to work the goo onto the bedding surface of the opening and the glazing.  By breaking all surface tension to both pieces before assembly you now only have to mate goo to goo and this all but assures no bubbles.  Etching as Mike suggests certainly increasing bonding.  I have never seen it as necessary.

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