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Glass Breakage and Seal Failure

Objective :

  • To understand the causes of glass breakage
  • To be able to select film for application on various glass types and avoid causing glass to break.
  • To be able to read the Film to Glass Application Sheet.
  • To be able to fill out a Film to Glass Application Checklist

 What we will cover:

  • Solar energy and thermal stress
  • Types of glass breakage
  • Framing problems
  • Shading
  • IG Units and film
  • Low-E glass
  • Film to Glass Application Chart and Checklist
  • Warranties

Glass Breakage and Insulated Glass (IG) Unit Seal Failure

  • THE BOTTOM LINE: If glass breakage and/or IG unit seal failure problems did not occur before film installation, it is unlikely that glass will break after the installation of the proper film
  • The key – choosing the right film for the window and glass type
  • As a window film professional, you need to become knowledgeable on glass breakage.
  • You are the customer’s source of information for film purchase. You must insure the success of a window film installation.
  • Early in the window film industry, glass breakage and IG Unit seal failure were an issue.
  • To avoid glass breakage after a film application you must know why glass breaks and how to select the appropriate film.

Glass Breaks!

  • Glass is brittle and breaks under stress.
  • Any force that tries to pull the glass apart causes stress.
  • Types of stress
    • Impact
    • Thermal stress
    • Compression
    • Building/flexing
    • Thermal expansion
  • Glass is brittle and breaks under sufficient stress.
  • Any force that tries to pull the glass apart causes stress. Glass is prone to many types of stress.
  • Wind, hail, impact with an object or person and a building movement/flexing are types offeree that cause windows to break.
  • Two other types of glass breakage.
    • Thermal stress and
    • Thermal expansion.
    • On rare occasion, this is the type of breakage occurs after film installation.

Window Film Got A Bad Rap!

  • In the past, dark or highly reflective films absorbed excessive heat.
  • The absorbed heat caused a temperature increase in the glass
  • In the past, dark or highly reflective films were the only way to achieve heat rejection at the window.
  • These dark reflective films offered impressive solar energy rejection performance.
  • They often created excessive thermal absorptance within the glass.
  • Thermal absorptance causes the temperature of the glass to rise.
  • Increases the risk of glass breakage and/or insulated glass (IG) unit seal failure.

 But with the right film…

  • You get solar performance and minimize glass breakage
  • Today’s films offer more options
  • Today your customer, iis looking for other solar options.
  • Tint Depot technological advances provide new options.
    • No longer are dark or highly reflective films the only choices for impressive solar energy rejection.
    • Best of all, when the proper film is selected, glass breakage and/or IG unit seal failure is minimized.

 Glass Breakage After Film

  • Installation of the wrong film
  • Flaws In the glass
  • Flaws at the edge of the glass
  • Imperfections or expansion problems In the framing
  • In cases where glass breakage is reported, installation of film was not the sole cause.
  • The causes are usually are related to:
    • Installation of the wrong film
    • Flaws in the glass
    • Flaws at the edge of the glass
    • Imperfections or expansion problems in the framing

Solar Energy and Windows

  • Sun warms the glass
  • Glass absorbs some energy
  • With film glass can absorb additional energy
  • When the temperature of the glass rises too high

– Glass can break
– IG units can fall


  • The sun naturally warms glass because the glass absorbs some of the solar energy striking it.
  • After the installation of a film, solar absorptance in the glass may increase.
  • This raises the temperature and increases the chance of glass breakage and/or IG unit seal failure.
  • Tint Depot offers a wide selection of high tech films that provide impressive performance without raising the temperature of the glass.
  • To select the right film, it is helpful to first understand what happens when solar energy strikes a pane of glass.
  • Window film added to a window changes the way a glazing system reflects, absorbs and transmits solar energy.
  • Excessive heat absorption thermal expansion.
  • Thermal expansion causes the glass to expand against the seal. The pressure against the seal can cause the glass to break.

Thermal Stress

  • Caused by heat build-up in part of a pane of glass when other parts are cooler
  • Glass is cooler behind the frame or when shaded
  • Thermal stress refers to heat buildup in part of a pane of glass while other areas of the glass remain cooler.
  • This temperature imbalance causes the glass to expand in one area while resisting expansion in cooler areas.
  • These opposing forces cause the glass to pull apart.
    • Known as thermal stress.
    • Thermal stress and the related problems from shading, rapid temperature changes, imperfect glass and framing can cause more stress than a specific piece of glass can take

Imperfect Glass

  • Prior imperfections

– Small imperfections in glass surface
– Chips or cracks at the edge

  • Imperfect glass is one of the major reasons glass may break when the appropriate film has been installed.
  • Imperfections exist in the glass long before the film is installed. In the rare case when this happens, the heat the film causes the window to absorb is just enough additional thermal stress to break the glass.
  • There are different types of imperfections:
    • Small imperfections in the glass surface
    • Chips or cracks at the edge of the glass.
    • Imperfections in the glass surface come from the manufacture of the glass.

Impact Fractures

  • Leaves a tell tale sign of the blow
  • A fracture from impact leaves a tell tale sign of the point of the blow such as in the two drawings below:

Edge Stress

  • Chips or cracks In the glass hidden under the frame.

– Film on the window stresses these Imperfections shaded by the frame,

  • Ability of glass to absorb the additional absorbed heat from film relies on the prior condition of the edge.
  • Pre-existing conditions such as chips or cracks at the glass edge can be hidden from view by the frame.
  • The stage is set for an edge stress fracture when the glass is first cut or installed.
    • May not be an issue until film is installed and additional aborbed heat causes a greater difference in surface temperature than glass experienced before the installation of the film.
  • The ability of glass to resist increased absorbed energy and is determined by the glass edge strength. A straight, clean-cut edge is the strongest. The edge strength depends on glass:
    • Size
    • Thickness
    • cutting method
    • edge treatments
  • Edge strength is reduced by such treatments as grinding, polishing, nipping or seaming.
  • Edge strength can boil down to the skill of the original glasscutter.
  • Any scratches, nicks or other imperfections along the glass edge will reduce the amount of stress that a particular pane of glass can withstand.
  • Notice how that crack originates at the EDGE

Framing Problems

  • Thermal differences behind frame
  • Glass can break If It Is too tight In the frame
  • Frame too tight – not enough edge clearance
  • Glass is cooler behind the frame.
    •  Shaded from the sun
    • Causes a temperature difference in the glass surface
    • If edges under the frame are imperfect, greater chance for glass breakage from the additional absorbed heat of the film. This is referred to as edge stress.
  • Glass can break if it fits too tightly in the frame.
    • Tight frames do not provide adequate edge clearance to accommodate increased thermal expansion.
    • A tight frame reduces the ability of the glass to resist thermal expansion and stress by as much as 50 percent.

Shading and Temperature Change

  • Uneven and very dramatic temperature difference across the surface of the glass

– Usually a has a distinct shade line
– Glass under a frame
– Glass loses 50 psi per degree temperature change.

  • Thermal stress fractures occur where there no imperfections in the glazing system.
  • This group of thermal stress fractures is caused solely by uneven and very dramatic temperature differences across the surface of the glass.
    • Caused by partial shading of the window by trees, structural columns or other buildings.
    • The line of shade that could cause this type of break is usually a distinct, hard line as opposed to a feathery shade line created by leaves.
  • Rapid temperature change can cause a thermal stress fracture in perfect glass.
    • This would occur in when very cold air dumps on a hot window. An example is an air conditioning vent that does not diffuse the air well.
    • In some high altitude areas, such as Denver, wide temperature swings between day and night temperatures will induce a break in the window.)

Other Reasons Glass Breaks

  • Not enough clearance between blinds and glass
  • Air conditioning vent striking a hot window
  • Problems may occur due to some unique situations.
    •  minimal space between blinds and walls may create a heat trap, preventing adequate air circulation to carry away trapped heat is blocked by the window treatment.

IG Units and Absorbance

  • Film Is on surface 4 of an IG unit
  • Heat is emitted into the air space and is trapped
  • Window films are typically installed on the room side of the glass


  • Construction
    • Desiccant Fill
    • Metal Spacer
    • Secondary Seal
    • Primary Seal
    • Frame
  • In an IG Unit film is installed on surface number four on an IG unit (see IG unit diagram)
  • When film is installed on surface number four; heat emitted from the solar absorption on the filmed surface can build up between the panes.
  • Heat becomes trapped between the two pieces of glass.

Heat is Trapped in an IG Unit

  • Trapped heat can cause different rates expansion In the two panes of glass
  • Expansion and contraction over time degrades the seal
  • Thermal expansion may differ between the two pieces of glass.
  • One pane may expand more than the other.
  • This causes uneven pressure against the seal.
  • The daily expansion and contraction of the glass during the course of normal temperature changes in a day can degrade the seal over time.

SIGMA Tests IG unit

  • Routinely tests IG units
  • 1 in 100 of even the best IG units fail prematurely
  • The Sealed Insulating Glass Manufacturers Association (SIGMA) performs tests on IG Units for failures.
  • Even the best IG units fail prematurely at a rate of 1 in 100.
  • Lesser quality units and older units failed at 15 in 100

IG Units With Film – No increase in failure

  • A SIGMA consultant tested IG units with film
  • Tests with film on the unit showed no increase in breakage
  • The Association of Industrial Metallizers, Coaters, and Laminators (AIMCAL) hired a technical consultant from SIGMA.
  • In tests on IG units with film, he concluded that although a larger sample is required, there were “no detrimental effects of the use of window film on quality manufactured sealed units.”

 Low-E Glass

  • There is little standardization in Low-E glass
  • Low-E coatings
    • Pyrolytic (Hard)
    • puttered (“Soft Coat”)
    • More Film friendly

The surface of the IG unit that has the Low-E coating is critical to film performance …

  • Surface 2 Film Friendly
  • Surface 3 Film Un-Friendly
    • Construction
    • Desiccant Fill
    • Metal Spacer
    • Secondary Seal
    • Primary Seal
    • Frame

Film-To-Glass Application Chart

  • A risk assessment tool
  • Simplifies the film selection
  • It takes into account the three things that affect glass breakage.

– Film type
– Glass type
– Window type

  • The film to glass chart assesses the appropriateness of a film to glass application on a broad analysis of the spectral characteristics of each unique type of film
  • It is a risk assessment based on which films work on four window types:
    • Clear single pane
    • Tinted single pane
    • Clear double pane
    • Tinted double pane
    • Low-E
  • Instructor: Hand out a Film to Glass Chart

Film-to-Glass Application Chart

  • Guides your selection of film for specific types of glass
  • Specifically relates to warranty coverage
  • Simplifies the film selection process,
  • Provides information that is critical to making an informed film choice and a successful installation.
  • Basically the chart identifies types of warranty coverage available for certain films on specific windows.
  • Now that you understand why glass breaks you can see why it is difficult for a manufacture to provide glass breakage cover on any film applied to any window.

Using the Film-to-Glass Chart

  • The suitability of all Tint Depot on four glass types plus Low-E windows is addressed.

– Clear Single Pane
– Tinted Single Pane
– Clear Double Pane
– Tinted Double pan

  • Remember we learned there are three things that Impact glass breakage: film type, glass type, and window construction. Each of these parts contribute to the solar absorptance of the glazing system.

Films -to-Glass Ratings

1 = Pre-approved for glass breakage and seal failure

2 = Not pre-approved

– may cover for a fe

3 = No seal coverage available

– may cover glass break for a fee

4 = No coverage available

  • There are basically four types of warranty coverage for glass breakage and IG unit seal failure:
    • no extra charge
    • coverage with approval
    • coverage for glass breakage but not seal failure for a fee
    • no coverage available for glass breakage or seal failure available

Low-E details

  • LEG (Low-E caution) indicates possible glass breakage and seal failure

– Surface 2 LEC film pre-approved
– Surface 3 pre-approved with SC less than .70
– Surface 3 not approved with SC greater than .70

Architectural Film Warranties

  • With proper application of film to glass, coverage include:

– Film
– Reasonable labor up to original invoice value

Architectural Product Warranties

  • Product warranties

– Manufacturing defects (bubbling, cracking, crazing, de-lamination,change of color)
– Color covered only on products without dyed components

  • Non-transferable
  • Improper film installation

Residential vs. Commercial Product Warranties

  • Residential applications receive less wear and tear

Residential Product Warranties

  • Length of term

– Tint Depot pure component films (Lifetime or 10 year)
– 7 year dyed films
– 5 year (NR auto films used in architectural applications)

Commercial Product Warranties

  • Length of term

– Pure component films (10 year)
– 7 year dyed films
– 5 year (NR auto films used in architectural applications)

Safety Film Product Warranties

  • Length of term
    • All safety films(10 year)

Glass Breakage and IG Unit Seal Failure Warranties

  • Dependent on film type
  • Glass breakage and seal failure are separate coverages
  • With approved film from film-to-glass application guidelines
  • Or with approved film-to-glass application checklist
  • Tint Depot does not warrant any window film against glass related injuries
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