sealing acrylic windows: attempt no 4

snowleopard

snowleopard

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I'm about to replace some windows in the hope that I can stop the leaks. Very little success so far. My windows are pretty big so there's a lot of expansion to handle.

1. Sikaflex 295UV - A horrendous price. The bond failed where the special primer on the window came off after a year or so.

2. Neoprene tape - self adhesive, silicone to bond to window. Silicone bond failed

3. Neutral-cure silicone - again bond to window failed.

The one thing that has been fairly successful is the doghouse windows (which don't need to be watertight!) stuck on with generic polyurethane mastic. Hell of a job prying the bits loose when one got hit by a flying block and shattered.

What should I try next?
 
snowleopard said:
I'm about to replace some windows in the hope that I can stop the leaks. Very little success so far. My windows are pretty big so there's a lot of expansion to handle.

1. Sikaflex 295UV - A horrendous price. The bond failed where the special primer on the window came off after a year or so.

2. Neoprene tape - self adhesive, silicone to bond to window. Silicone bond failed

3. Neutral-cure silicone - again bond to window failed.

The one thing that has been fairly successful is the doghouse windows (which don't need to be watertight!) stuck on with generic polyurethane mastic. Hell of a job prying the bits loose when one got hit by a flying block and shattered.

What should I try next?
Click to expand...

Fwiw, I was speaking to somebody who had just changed his windows. He said to use Sikaflex 291i but to apply it and then wait 2-3 days before tightening it down.

His plexi seemed to have been very well done.
 
Polyurethane sealant.
But the key is to ensure the active layer of sealant is at least 1mm thick, pref 2mm, so that it has a reasonable chance of flexing without peeling off one side or being stretched to breaking point.
You can achieve that by spacing the window away from the substrate, or routing a recess for the gunge to sit in.
 
lw395 said:
Polyurethane sealant.
But the key is to ensure the active layer of sealant is at least 1mm thick, pref 2mm, so that it has a reasonable chance of flexing without peeling off one side or being stretched to breaking point.
You can achieve that by spacing the window away from the substrate, or routing a recess for the gunge to sit in.
Click to expand...

When I used the Sikaflex it recommended 3-4mm thickness. Given that my biggest windows are over 1 metre wide, quite a lot of depth is needed to allow for expansion.
 
snowleopard said:
When I used the Sikaflex it recommended 3-4mm thickness. Given that my biggest windows are over 1 metre wide, quite a lot of depth is needed to allow for expansion.
Click to expand...

Perhaps "bite the bullet" and divide the window widths into, say, thirds, with a joint there just to provide extra expansion flexing? I'm sure the divide could be made less obvious than fake leaded windows... ;-)

Mike.
 
snowleopard said:
Given that my biggest windows are over 1 metre wide, quite a lot of depth is needed to allow for expansion.
Click to expand...

My main cabin window is 1100mm long and has stayed watertight bedded on the arboseal GZ butyl tape. You haven't said whether your windows are held in only with adhesive or if they are also screwed, framed etc. It makes a difference.
 
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