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Curved (bent) Glass for Windows

9/20/21       
Chad Member

Website: http://www.adamsarch.com

We are fabricating curved double hung and fixed windows for a historic home. The sash are already made and the curved (bent) glass arrived today.

We test fitted the first 15 units and the glass matched the radius in the middle of the sash but the glass flattened out on the sides (see pictures). We checked the radius of our window sash and it is a true radius compared to the variance in the radius of the curved glass.

How would you guys handle this? Glass company says it is within tolerance.

How do you suggest I fill the gap between the window profile(sticking) and the glass without water infiltrating the window and probably the home at some point. This is a huge issue.

Earlier this year we purchased curved glass from the same company and had no problems at all. The glass matched the radius of the window sash perfectly. I questioned the VP of the glass bending company regarding the difference between the two projects and his response was that we got lucky the first time.

I have 10's of thousands of dollars in glass and I don't think the glass company will help out. The project was supposed to be completed 2 weeks ago and now I have to figure out how to explain this to the contractor. New glass is going cost a lot of money and as with everything the now, the lead times are probably pretty far out.

I feel stuck. Looking for advise on how you guys would handle the situation.

Thanks, Chad


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View higher quality, full size image (1512 X 2016)


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9/20/21       #2: Curved (bent) Glass for Windows ...
RichC

I would either bandsaw a piece of wood to fill that up, or talk to the glass company about a bedding or setting tape. The quality of the bent glass depends on the technology. If they are old school and just use a 3 or so steel forms and a sheet of thinner steel to line it, or if they have an hydraulic mold system to hold the hot glass till it sets makes the difference. Do you provide curved patterns for what you want? If you insist on a better fit, they have to run a wider piece of glass and then trim off the sides so the weight of the wider piece of glass forms a cleaner radius. They may loose pieces during that trimming, so the price goes way up!!

9/20/21       #3: Curved (bent) Glass for Windows ...
Chad Lueken

Thanks for the reply Rich,

I don't know the technology the glass company uses. With the results we received this time, I would say they are old school.

We provided highly detailed 3d drawings to the glass company. In return, the glass company sent us back their own highly detailed shop drawings that we reviewed and signed-off.

I am ok with paying more money for the right product. This glass does me no good and is going to cost me big time in the long run (either re-work or buying new glass). If we use this glass, the final product is not going to look good and I don't know if it is going to hold out the water.

9/20/21       #4: Curved (bent) Glass for Windows ...
TonyF

Chad:

A real dilemma. I suppose that new sash is a cost/time problem, and that the glass company is unwilling to remake the glass, or even attempt to adjust it.

If you are stuck with what you have, some questions:

Does the glass fit well in the sash otherwise, and the only problem is the radius?

How big is the glass, how thick is the glass, and is it tempered?

Are the glass pieces uniform unto themselves?

Does the existing sash radius register to an existing radius in the building wall, or is there room to maneuver?

The difference looks to be about 3/16" at its worst point, according to your photo. Perhaps the chamfered stop on the sticking could be flush trimmed off, and a new piece of the chamfer run and glued in its place to match the glass curvature, and adjust the flat of the sticking and the interior stops accordingly on the radial portions. If the glass is consistent, this could be done with templates.

If you are feeling lucky, and if the glass is not too big, not too thick, and not tempered, you might try making a form, use a propane torch to heat the ends of the glass that are not radial, and see if you can get it to conform to the form by coaxing it with an oven mitt. This has worked for me for small pieces, but is risky for anything of any size, and if you don't have extra pieces.

The bandsawn fillet/bedding compound might be the obvious, quicker fix. Perhaps, if the glass is consistent, you could make an inner form that matches the glass and use it as a dam, and fill in the difference with epoxy, and flush it up to the sticking after it is set. Wax paper will keep the filler from sticking to the dam. Since it all looks like it gets painted, you may have some leeway.

Just trying to help. Sorry if it sounds too absurd. It will not look the same as it would if everything fit properly, with the concentric lines of radial construction that we all love.

Good luck.
TonyF

9/21/21       #5: Curved (bent) Glass for Windows ...
Adam

Interesting comment from the fabricator.

"You got lucky last time" or
"You got unlucky this time"

The more obvious perspective is that his company didn't manufacture the product to the drawings. I don't believe in luck.

What's the stated tolerance? Contract? Payment?

The only curved glass I've ever been involved with was for a boat cabin house. That was new school and was curved in two planes. Spot on matching a complex fibreglass shape. I helped install them, so I've got nothing more. I was very impressed.

9/21/21       #6: Curved (bent) Glass for Windows ...
Chad Member

Website: http://www.adamsarch.com

I appreciate the following responses.

This is a fairly large project. It consists of 30 pieces of bent glass. The sizes vary from smaller 36" x 15" to very large 52" x 28". It is 1" thick using 1/4" thick glass for the IG unit. The sash are 2-1/4" thick. The sash are fabricated from Mahogany for the painted windows and White Oak for the first & second floor that are stained on the interior.

The glass is paid for. They would not release the shipment until I wired them money.

I have attached both the quote document as well as the final shop drawing sign-off. The more I look at this, the more it does not smell right. On the quote document it states that the glass will be provided with a true radius. This glass does not have a true radius. Please also look at the tolerances on the quote. It is an 1/8" on either side. So for a 1" thick piece of glass it can be 1-1/4" thick out of tolerance.

Typically we usually put a bead of caulk on the glass rabbet and lay the piece of glass in it. The weight of the glass squeezes the caulk out and provides a good seal.

Here are couple ideas that we have to glaze these windows.

1.) install the glass and fill the gaps with Abatron or Putty that we use on other traditional projects.
2.) Band saw out shims of wood to fill the gaps and then caulk the crap out of it.
3.) Purchase new glass that fits our radius.

I am really concerned with keeping water and moisture out long-term. I am afraid the water will either infiltrate the house or the insulated unit will go bad due to exposure to moisture.

Looking for advise:
1.) How would you deal with the glass company that supplied the glass?
2.) Would you get the contractor involved right now or try to find a glazing method first.
3.) Due to the chances of future issues, order new glass that fits the radius. Do you have recommendations of a Bent Glass Suppliers.

Thanks,

Chad


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9/21/21       #7: Curved (bent) Glass for Windows ...
Mark B

Id say your going to have to fight them. "True radius - no flat legs" does not look like what you have.

9/21/21       #8: Curved (bent) Glass for Windows ...
RichC

I would start with a detailed drawing or pattern of what you received. Involve a local glass company, professional architect, or general contractor to certify that what you received is out of tolerance. If you use an architect, he can stamp the response letter. Send it certified mail and give them a date to respond by. No response? Then a letter from your lawyer. Those are expensive pieces of glass, it's worth seeking compensation. Maybe check with your lawyer first. You may be forced to order from another source and the lawyer can tell them in the letter you will be seeking damages and reimbursement from them for the order from another company.

9/21/21       #9: Curved (bent) Glass for Windows ...
Bruce H

It's an "historic" home, the original glass and wood windows were never perfect in the first place. The effort to sue the glass company won't get your project done. I would cut fillers and make it work. The new glass will look just as good as the original glass did.

From the looks of this video I am guessing this is not what you got.

How to Bend Glass

9/21/21       #10: Curved (bent) Glass for Windows ...
Mark B

My guess is at 2:29 in your video, this never happened. Especially as these are IG so a matching pair had to be bent.

Making them work is fine but Im sure Chad is concerned with who holds the liability if it all goes bad in 6 months, a year, two, or five.

9/21/21       #11: Curved (bent) Glass for Windows ...
David R Sochar Member

Two ways to work wood: Subtractive, and Additive.

With 2-1/4" thick sash, you have some room to move, perhaps. 1. When the glass unit is in place, how far from contacting the rabbet is the glass on each vertical edge? If the curve flattens out as it approaches the vertical edge, and if the glass goes in from the outside, then it will land/contact on the center of the top and bottom curve first, not touching the vertical sides.

Remove wood from this center area, tapering off as you approach the stiles. Worse case scenario is you loose the sticking profile, so you may have to remove the sticking, then remake it to fit the glass on one edge, and the radial ideal on the other surfaces.

We use a silicone sealant that easily can seal up to 1/8" gaps, and it cures like hard rubber. It is adhesive so it bonds very well. A < 3/16" caulk line on each vertical edge would not cause me to loose sleep.

We have used it more than once to bridge gaps over 1/8" - typically in old sash, curved and salvaged, never expected to be pretty. I would bet not 1 in 1,000 ever see such fixes.

Document everything, especially all the time you have so far, and will have in your fix. Have your attorney bill them for that amount, probably equal to what you have paid for the glass. Your goal is to have your -alleged - vendor state in court, that you "got lucky the first time". That type of arrogance will usually backfire.

9/22/21       #12: Curved (bent) Glass for Windows ...
Chad Member

Website: http://www.adamsarch.com

Again - thanks for all the messages.

We have come up with two glazing options to hopefully fill the gaps between the glass and the sash sticking due to the variance in the radius of the glass compared to the window sash.

1.) Fill gaps with glazing putty – This putty is used to glaze windows like they did in historic traditional windows. We are using it as a filler for the gaps of the inconsistent radius.

2.) Use butyl glazing tape and then caulk the top of the glazing tape with siliconized acrylic that is paintable.

Please see pictures of both.

Which one do you guy think would be the best glazing method to seal these units?

Any other ideas?

My biggest concern is mitigating any water from entering the sash due to the variance in the radius that is causing the gaps. The last thing we need is water getting into the house due to a rain storm with straight line winds. Especially on the top floors and potentially ruining flooring, plastering, ceilings, etc. below.

We informed the contractor of the issue and they have been open to different glazing options to save the glass. Lead time is a huge issue due to the project being in a cold climate and it is starting to get cold.

Thanks, Chad


View higher quality, full size image (2016 X 1512)


View higher quality, full size image (1512 X 2016)


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9/22/21       #13: Curved (bent) Glass for Windows ...
Mark B

Ive always been a fan of Butyl tape in the places it works well but it does dry-out and shrink over time but still remains a bit pliable. Moreso when fully exposed so covered with sealant would help. Glazing compound would seem to me to require more maintenance than most would care for but in a historic building hopefully maintenance is high on the list.

I would personally go with something like Sikkaflex 221 or an equivalent if that isnt compatible with your IGU sealant. With a urethane and some tools, a little solvent, and good technique you can polish that stuff down like a gasket and no sag/shrinkage and it holds up for a very long time especially if painted.

9/22/21       #14: Curved (bent) Glass for Windows ...
Harold Pomeroy

Chad, It looks like there's no caulking around the glazing tape. You probably know this, but be sure the glazing compound can never reach the insulated glass sealant. It can cause insulated glass units to lose their seal.

This post has been helpful to me. The next time I order bent glass, I will specify the tolerances. I think I will also take a sash drive down there and pick it up. It's worth it to make sure it fits if the company has that attitude.

9/22/21       #15: Curved (bent) Glass for Windows ...
Mark B

I'd agree.. shipping a CNC or shop cut ply template for each unit with a notation that if the unit doesnt fit the template it will be refused would be wise. Hind sights always 2020 and when you get a batch that are perfect who'd think to do such a thing on a second round.

9/22/21       #16: Curved (bent) Glass for Windows ...
BH Davis  Member

Website: http://www.bhdavis.net

Personally I think the only way to deal with this is to get the correct glass. This company is apparently not capable of producing it so you probably will have to go elsewhere.

The glass doesn't match the drawings......period. Anyone who deals with curves on a regular basis knows about the ends of a forced bend curve being straight. That is an unacceptable result. I wouldn't have been in business very long if I had been supplying our curved mouldings with straightened ends. I often explained the phenomenon of straight ends to people by grabbing a long 1/4" dowel and bending it by grabbing the ends. It was pretty clear that the last 6" on both sides were straight.

Unfortunately it sounds like you aren't going to get anywhere with this supplier without a lawyer involved. An awful route to take but it may be the only way to get this resolved on a financial level. Then re-order the glass from a manufacturer that understands how to make proper curves.

Good luck,
BH Davis

9/23/21       #17: Curved (bent) Glass for Windows ...
Adam

Chad,

I hate to ask, but it would determine my response to your situation.

What type of money in glass are we talking about? $5k or $10k?

9/23/21       #18: Curved (bent) Glass for Windows ...
Chad Member

Website: http://www.adamsarch.com

Thanks for all your comments and suggestions.

We have decided to keep the glass and move forward with glazing the sash.

I am very anxious with the situation because the shop has worked so hard to make these beautiful windows and one of the last components of the project did not come together like it should have. I think the team was yearning for that feeling you get when a project goes right and you just nailed it. We were on that path. The glass issue put a shadow over the project.

Whenever we have an issue in the shop or the office we document the issue using a form called "Lessons Learned". We used to call it "Cost of Quality" and we tally the time and materials it cost the business as well as the Opportunity Cost to the business. The Lesson Learned on this project is that I should have pressed harder on stating our acceptable tolerances. In a conversation with the glass manufacturer, he said you created a radius with a +/- 0 (zero) tolerance. He continued to explain that he can't make curved glass to a zero tolerance. I disagreed with him that we needed a zero tolerance. I told him that I was expecting a piece of glass that had a true radius with no flat spots. I can deal with the piece of glass that is not perfect, but to make up for a flat spot that causes a 3/16" - 1/4" gap is quit alarming.

The glass manufacturer knew this glass order was for historical wood windows when they quoted the project and not a commercial type project where the tolerances are not as tight. That should have been an "A ha" moment for them and they should have either quoted different glass or kindly said this project was not for them.

It goes back to a question I ask myself as a business owner: Do I try to keep my customers out of trouble or do I let them figure it out themselves. If I can help or recognize the situation, I try to help the customer. I wish this glass manufacturer did the same thing for me.

Soon this project will be complete and we will move on to the next. I will take what I learned and hopefully use it on future projects.

Thanks again,

Chad

9/23/21       #19: Curved (bent) Glass for Windows ...
Bruce H

I have been watching glass manufacturing videos since this thread started. An eye opener. Curved auto glass is made to exacting tolerances every day so it is possible. Seems to me that if the mold was perfect and the glass is heated correctly it is possible. I think your glass wasn't heated enough to conform to the mold, how else would there be flat spots? But, what do I know? Hope it all works out.

9/24/21       #20: Curved (bent) Glass for Windows ...
David R Sochar Member

Lessons Learned is a great tool. Good for management, as they know when to be cautious in the future, and then what costs might need to be taken into account. Also good for the shop techs so they know what to watch out for and the presence of such a project will spur problem solving ideas before it is even built.

We call everything we do "Process", but wave large red flags when we have a problem that needs to be solved - either before it is created, or after it has reared its mangy head. We enjoy problem solving and the challenges that bring it to us.

May your phone ring with more good work, and not window leaks.


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