Every fabricator strives to deliver perfect tempered glass. That is why you buy from them. Most of the time, they succeed in this perfection. Sometimes their in-house quality program will reject glass, but you never know this. What happens when they ship the glass and your foreman says, "Boss, we have a problem!" Could be you and the fabricator are working to different standards of perfect. ASTM C 1048-04 is the standard for Heat-Treated Flat Glass, either Heat-Strengthened or Fully Tempered. This is the puppy we should all be petting.
Last week we learned that flat glass isn't perfect, so if a fabricator tempers a piece of flagrantly flawed float (say that three times), and it still meets the standards, you own it. Tempering adds even more variables to the mix.
Let's read excerpts of the standard on distortion in glass:
7.4.1 "Thermally tempered and heat-strengthened glass is made by heating glass in a furnace to a temperature at which the glass becomes slightly plastic. Immediately after heating, the glass surfaces are rapidly cooled by quenching with air from a series of nozzles. The original flatness of the glass is slightly modified by the heat treatment, causing reflected images to be distorted."
7.4.2 "...Fully tempered and heat-strengthened glass that has been made in a horizontal furnace my contain surface distortion. Distortion will be detected when viewing images reflected from the glass surfaces.
7.4.4 "Sealed insulating glass units also exhibit distortion regardless of glass type. Air or gas, trapped in the sealed airspace between the panes, expands or contracts, with temperature and barometric changes, creating a pressure differential between the the airspace and the atmosphere. The glass reacts to the pressure differential by being deflected inward or outward."
The standard addresses concerns that we all have. It acknowledges that glass isn't perfect. Mostly, when it comes to scratches and rubs in glass, the flat glass standard C1036, applies. So if a scratch is not visible from 11 feet away, it doesn't exist. These standards are critically important to your business. Ask your fabricator for a copy, or go to ASTM.org, where you will pay a fee for a download.
The biggest issues with tempered glass is size tolerance and 'bow and warp'.
There are special sections that address both of these.
Here is a basic chart for size tolerance that should be adhered to:
Thickness.........Finished Size Tolerance, Length or Width, plus or minus
1/8 ......................... 1/16
3/16 ....................... 1/16
1/4 ......................... 1/16
3/8 ......................... 3/32
1/2 ......................... 1/8
3/4 ......................... 3/16
As this is a plus or minus tolerance, one side of a 1/2 lite can be full by an eighth, the other side shy an eighth, making the lite 1/4 out, and it still is acceptable.
The standard for bow and warp is based on the overall size and thickness of the finished lite. Let's look at the allowable bow in just two thicknesses,
Size(in) 20-35...35-47...47-59...59-71...71-83...83-94...94-106
1/4 ..... (.12).....(.16) .....(.20)....(.28)....(.35)....(.47).....(.55)
3/8 ..... (.08)......(.08)....(.16).....(.20)....(.24)....(.28).....(.35)
A lite of 1/4 tempered, 48 x 96, can be warped over a half-inch! Do you find this acceptable? The standard does, and if your glass comes in with this warp, what do you do?
Talk with your fabricator early-on in your relationship and understand what tolerances they ascribe to. Do they have a tighter standard for a high-quality piece like a shower door or table top, than they do for general glazing? This is the key. Know what your fabricator expects of themselves and you will know the standard you can promise your customers.
One last thought, these standards are not law. If you make a contract with a customer to provide perfect glass, that is fine. Buy you probably will need to order two or three lites to get one that is dead-on perfect. If you try to always sell perfect, you better adjust your pricing now.
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4 comments:
Welcome back Paul,
We both know that the 11 ft spec. is unreasonable, especially when dealing with shower enclosures where bathroom sizes are shrinking. A lot of these jobs are less than 11ft wall to wall. What now. Well once again, you are correct... a teaming with your fabricator(s) to know what their specific tolerances are is mandatory to ward off problems with the customer. That and customer education as to expectations, are imperitive to a good relationship (and speedy payment).
I (we) know fabricators that subscribe to 3 ft in NORMAL light, not high intesity Halogen bulbs 6" obove the job, - YES LIGHTING IS A HUGE CONSIDERATION ON ANY JOB- but be prepared to pay for these tighter tolerances. Don't expect to go to the low bidder and get top quality.
What is the old saying? goes something like this....Low cost, Quality and on time delivery....you can achieve 2 out of 3 at best.
Jim F
Perfect glass requests are usually squashed at the sales desk. If not, more education is need in that department. The second I hear "I have a picky/perfectionist customer" I warn my customer of the ultimate outcome-many call backs-and suggest that he call a company that sells perfect glass, because we do not offer it. And he should educate his customer to this reality. Nothing is perfect!
I just wanted to chime in here. We have actually run into those people who have to have "perfect" tempered glass without any scratches. This was after they have discovered their new tempered glass was scratched up pretty bad from...whatever. We have our theories! However, we have actually come up with a way to completely and quickly "resurface" large areas of tempered glass in a very short time. In some cases, about 15 sf an hour has been resurfaced without leaving any swirls, haze, or even distortion! I know, sounds too good to be true. All you have to do is ask some of our references. We've recently returned from Waikiki Hilton where we resurfaced an entire sliding door in 3 hours! It looked like someone hit it with some 80 grit sandpaper! ANyway, they were totally sold. Only 899 windows to go! Anyway, many references will confirm what I am stating. We're currently working at Jennifer Annistons new Beverly Hills home. Large Fleetwood glass doors scratched pretty good! Contact GW Associates, the GC in charge of the project and ask them about Unscratch The Surface. Thay didnt believe it could be done, especially because of the depth and magnitude of scratches and the view and the distortion issue. So, I'm just here writing all this so that people will know that it is actually possible now to resurface large areas of scratched glass that looks good even in early morning sun or sunset or halogen lights. Feel free to contact me with any questions. Thanks for reading this! Rick Evans www.UnscratchTheSurface.com
805-295-9020 rick@unscratchthesurface.com
People believe that glass just appears magically in their house with no human contact, and that is simply not the truth. So many times do I hear from clients that they are astonished to find scratches/defects/distortion in the glass as soon as it was installed. There needs to be an obvious statement coming from manufacturers that this is just not going to happen so that customers can lower their expectation and everyone can be happier in the end.
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