Mystery of the cracked windshield glass...

Hmmm, this is the first major problem that I've had with my 73 Silverton restoration. I'll post a couple of photos from when I was building the frame. It's completed and painted now.

In 2010 I installed the window glass in my new cabin. This cabin is much stronger than the original. I used Sika 206 g+p and Sika 296 to bond the glass into the windshield frame and Sika 206 g+p and 291 LOT to bond the structural parts of the windshield frame. I used the primer on the recommendation of a Sika rep that I spoke with. We determined that the proper use of the primer and adhesives/sealents would allow me to build a windshield assembly and tie it into the boat without the need for any screws. Since all the wood was painstakingly prepped this technique worked out well.

The glass has been in the boat for 1 year and a half. I'm still working on the restoration so shes not been in the water but in late 2009 after the glass was installed we moved the boat in the yard via a Travelift. If there was any flexing or movement issues I'd have expected them then. There were none.

The other day I noticed a crack in the bottom of the port side windshield glass. The glass is 1/8" laminated and the crack in in the inside pane. There was no impact or any other trauma that could have caused this.

I installed the glass on 1/16 neoprene pads and left about 1/8" all around for clearance.

Any thoughts as to why this happened or do I just have bad luck?

Also, and just as important.....For the time being I have other work to complete so I'm going to leave the glass alone as there is absolutely no water penetration of any kind. Eventually I'll have to get it out. I plan to use the hot putty knife trick to open up a seam in the Sika adhesive. I'd like to cut the glass out so that I can remove the sealant from the frame without the whole pane being in my way.

What would be the preferred way to remove the bulk of the glass pane?

Thanks in advance for any thoughts,

MIA

 

glass is very sensitive to edge pressure, most installations require large margins around the edges using flexible sealant. It is possible the opening was not quite large enough?

Does sealant hold the glass in place, or do you clamp it into place?

Also consider that wood will expand and contract with temp and moisture, dry climates could cause the frame to shrink and put pressure on the glass.

 

As Petros mentioned glass doesn't like it's edges fooled with. It's very common to see the lower edge crack or chip as this is the place gravity pulls it to in the frame. I try to avoid placing glass in frames on site, preferring to remove the frame, lay it flat on a table then drop the glass in, so it floats uniformly around all edges, while the goo cures (a few weeks). Then the assembled window frame is reinstalled in the boat.

The usual culprits are not enough gap around the glass, as you'd expect. I'm not sure what the deal is with your frame, but I'll bet you could live with more gap.

 

Thanks for the replies gentleman, when I replace the pane I'll allow slightly more for expansion.

Looks like the difficult task will be removing all the sealant and glass without damaging the frame.

Thanks Again,

MIA

 

To seat a glass panel you must install spacers all around the perimeter of the frame....both the edge surface and the mating surface. These rubber spacers prevent hard spots from forming and keep the joint from becoming calking staved. The spacers can be bought at a glass shop or hardware store. Uses many.

In future epoxy prime the frame. The epoxy hardens, waterproofs the wood and makes window removal easier. On many window installations weatherstrip type tape is used on the inside edge. This installation is cleaner because the tape prevents caulikig squeeze out on the inside , produces a clean joint and keeps the joint from becoming caulking starved. .

Consult Boatdesign net contributior Rwatson handy link thread and window bedding is well covered.

 

missinginaction

Try removing the glass with an Fein mulitpurpose tool (or equal) with a convex cutting blade. Hold the blade tight and square to the glass. It will zip right thru the sealant.

In commercial windows you would never use a setting block thinner than 1/8" set at quarter points. I would check with your glass supplier to check on the suggested setting block thickness and durometer.

I hope this helps.

Allan

 

I see how a multipurpose tool such as a Fein would make this removal much easier than I thought.

Thanks,

MIA

 

You remove glass with a cheese knife...wire and two handles.

 

The glass is cracked, so you don´t need to save it. Smash it with a hammer, and pry the bits out.

 

That's a good point Gonzo. I was just thinking I'd try to be neat about it. You might be right though....sometimes quick and messy works well. Now where's that shop vac?

MIA

 

I tarp over both sides and smash the glass.

 

We usually removed cracked glass by putting lots of sticky tape on both faces and then breaking it. The best way to break glass is to hit it with a pointed object rather than a hammer. You can sometimes take out the whole panel with almost no loose chips this way. you may need to knife the laminate, but a heat gun can sometimes soften it enough to pull apart.

 

It's laminated glass, so it has a plastic film in the middle.

 

A hot knife works well and does little damage, plus leaves the glass intact so it can be used as a template, which in this case should probably be smaller. A wire works, though wouldn't be my recommendation on this type of frame, as it can damage wooden frames pretty easily. With a multi tool, I'd be afraid of digging into the wood or making a groove. The usual method of using a hot knife is the least likely to damage the wood. I have modified soldering iron tips (home made tips) that can be sharpened and to a fine job or this. Even some elbow grease with a utility knife and straight edge blade, will yield results eventually, though it's easy to slip and leave a deep scratch.

On a windscreen that size, I'd heat up a wide putty knife (6") with a torch and press it to the glass, while shoving it into the sealant. This will melt the contact there. The next pass would be along the gap groove where the edge of the glass lives. Turn it over and do it again with the putty knife against the glass and most of the sealant will have melted or burned off. A utility knife can free up the rest.

 

Yeah PAR, with all respect to Gonzo I think like you do especially with the glass setting in that cavity I built into the pillars. My greatest concern is not damaging the pillars.

A putty knife would work but I'm thinking that a drywall taping knife might be even better at least for the first pass. Really thin.

Thanks for the advise guys,

MIA