Geyser Posted May 5 Report Share Posted May 5 Hello. I recently installed Johnson Daylight Natural DN 50 on a couple of windows. Solar energy rejection is 39%. The windows are double pane and the glass is supposed to be tempered 4mm + tempered 6mm. The roof overhang shades the top 1/3 - 1/2 of the windows. However, a few days after installation I noticed that one of the glass has cracked, presumably due to thermal stress. Should I remove the film from the rest of the windows? I installed the film on 24 of these windows (6 tiny houses) so now 1 out of 24 is broken. Or is it more likely that I just got unlucky and the glass had a defect? Is shading from the roof overhang such a big factor? The glass cracked. Is it really tempered? I thought tempered glass would shatter, but not crack. Thanks! Link to comment Share on other sites More sharing options...
Tintguy1980 Posted May 5 Report Share Posted May 5 (edited) The crack indicates thermal stress, however, the edge of the glass may have an imperfection (bur or clam shell chip). The crack does run 90 degrees out from the edge and curves as it follows any weaknesses in the pane itself. I have attached a pictured of what tempered glass looks like when it breaks and alongside it what a plate (or float) and heat-strengthened glass looks like when it breaks. The outer panel my be tempered should indicate so by a stamp etched on the glass surface in one corner. It should indicate tempered. Plate glass has no indicators, however, heat-strengthened glass will crack in the same manner as plate glass. I'm an unsure whether heat-strengthened glass requires a stamp. Tempered glass is 4 times stronger than plate and heat-strengthened is 2 times stronger than plate. 1 in 24 is indicative of edge imperfection. I could not find the solar absorption rate of DN 50, but if it is similar to competitive films, there should be no issue with that installation setting (including a straight line shadow). This, too, points back to edge imperfection as the cause. And finally, I spy drapes in a close position, correct? If so, it would be helpful to crack open during sun exposure; this to assist in allowing trapped heat between the glass and drapes to dissipate. Edited May 5 by Tintguy1980 eddiesagers, TintDude and Roach 3 Link to comment Share on other sites More sharing options...
Geyser Posted May 6 Author Report Share Posted May 6 Hey, thank you for taking the time to reply. It's greatly appreciated! Link to comment Share on other sites More sharing options...
Ryker Posted May 6 Report Share Posted May 6 Whatever that glass is that cracked it is NOT tempered. DN 50 is pretty high solar absorption and your saying shadows too so you probably need a more reflective film. Roach 1 Link to comment Share on other sites More sharing options...
Tintguy1980 Posted May 7 Report Share Posted May 7 Follow up: Attached is the performance data for Johnson's Resi/Comm window films and if you look to the bottom you'll see DN50 has a solar absorption of 39%, which is well below the threshold of concern which is generally accepted as 50% absorption (with no shadow). With a straight line shading from the roof this does increase the risk, which is usually low for straight line shading compared to other types. I've also attached a pdf of Johnson's film-to-glass chart which is used to determine how safe a film is. The thicker the glass the higher the risk; you say 6mm tempered and 4mm is the cracked one (interior pane). The question now is what compass direction do these panels face? In the end, I'll just suggest you hook back up with the person that installed it and get his input. He had to have been comfortable suggesting that film. I still believe it's a one off cracked panel and the rest will be fine. It takes 2 seasonal cycles to know for sure. Truly your call as to whether or not to replace with something lighter such as DN60. Here's more helpful info that helps you question the glass type on the interior; is it plate or is it heat-strengthened (HS). I believe it is plate and not tempered or HS. Why? Plate glass with suffer thermal shock if the edge temperature is different than the center of the glass by 50 degrees F. Heat strengthened requires 100 degree F difference, and Tempered requires 200 degree F difference. Ryker chimed in and that stimulated further review. Good Luck with this. johnsonFilmToGlass_2021.pdf TintDude and MikeMN 2 Link to comment Share on other sites More sharing options...
Ryker Posted May 8 Report Share Posted May 8 I was thinking it would be higher on the absorption.... Great info on the whole post though Tintguy MikeMN and Tintguy1980 2 Link to comment Share on other sites More sharing options...
klauskjrnet@gmail.com Posted May 24 Report Share Posted May 24 Did you install on the inside or outside? We always install the film on the outside (specially if it's double glass with air or gass between) If you install on inside it will be to much heat and crack is possible. good luck Link to comment Share on other sites More sharing options...
Tintguy1980 Posted May 27 Report Share Posted May 27 On 5/24/2024 at 8:23 AM, klauskjrnet@gmail.com said: Did you install on the inside or outside? We always install the film on the outside (specially if it's double glass with air or gass between) If you install on inside it will be to much heat and crack is possible. good luck The above post is a bit controversial and naive in nature. May I suggest improving technical knowledge by using a film-to-glass chart, IWFA's study on window film use on dual pane glazing systems, and glass itself. Air/gas used in dual and triple pane glazing systems has zero impact on what gets installed. Absorption rate of film and glass edge quality impact the aforementioned glazing systems most. The film used in the OP has absolutely no reason to be installed to the exterior surface. Neither do the vast majority of film products that carry an absorption rate less than 50%. Start searching for good quality information to better serve you and your clients. And finally, installing on the exterior maybe has a life expectancy of 5-7 years before seeing degradation. Properly installing a product deigned for the interior (on the inside) increases life expectancy up 20-25 years, depending on the quality of the film. MikeMN and doctor4766 2 Link to comment Share on other sites More sharing options...
MikeMN Posted May 31 Report Share Posted May 31 On 5/6/2024 at 10:08 PM, Tintguy1980 said: Follow up: Attached is the performance data for Johnson's Resi/Comm window films and if you look to the bottom you'll see DN50 has a solar absorption of 39%, which is well below the threshold of concern which is generally accepted as 50% absorption (with no shadow). With a straight line shading from the roof this does increase the risk, which is usually low for straight line shading compared to other types. I've also attached a pdf of Johnson's film-to-glass chart which is used to determine how safe a film is. The thicker the glass the higher the risk; you say 6mm tempered and 4mm is the cracked one (interior pane). The question now is what compass direction do these panels face? In the end, I'll just suggest you hook back up with the person that installed it and get his input. He had to have been comfortable suggesting that film. I still believe it's a one off cracked panel and the rest will be fine. It takes 2 seasonal cycles to know for sure. Truly your call as to whether or not to replace with something lighter such as DN60. Here's more helpful info that helps you question the glass type on the interior; is it plate or is it heat-strengthened (HS). I believe it is plate and not tempered or HS. Why? Plate glass with suffer thermal shock if the edge temperature is different than the center of the glass by 50 degrees F. Heat strengthened requires 100 degree F difference, and Tempered requires 200 degree F difference. Ryker chimed in and that stimulated further review. Good Luck with this. johnsonFilmToGlass_2021.pdf 88.9 kB · 7 downloads Very well said, Tintguy1980. Tintguy1980 1 Link to comment Share on other sites More sharing options...
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