Can vinyl cause cracks in windows??

[Phill Fenton]

Yes, I firmly believe that dark coloured vinyls on glass causes localised overheating resulting in the glass cracking – usually as a result of a tiny scratch or flaw already present in the glass.

Others may disagree 😕

there was a lot of "heated" discus ion about it here:-

https://www.uksignboards.com/viewtopic.p … sc&start=0

[Stuart Miller]

The quick answer is Yes, a dark vinyl which absorbs heat can cause a temperature difference in the glass. Its called thermal stress fracture.

The cracks will usually be a propagation of a crack which already exists in the edges of the glass from its cutting process. This is because standard Annealed (or Float glass) glass is cut to size by scoring with a diamond tip then snapped. This process causes many tiny invisible cracks along the edges which are usually no problem. However any of these cracks can potentially propagate at any time. The risk is increased by various factors such as size of the pane, exposure to the sun, shading of part of the glass by an overhang or tree but it can just happen spontaneously because the pane was installed slightly at an angle and it is just settling in the frame. So glaziers follow guidelines so as to reduce the risk of this happening. Notice I say reduce as there is no way of guaranteeing it.
This is with Annealed glass.

Toughened (Tempered or Heat Treated) glass however is very unlikely to suffer from this as each piece is made to size (rather than cut) and the heat treating process seals the edges removing all these cracks. Also as the glass has been heated to a far higher temperature than you would expect from solar absorption alone then again it is unlikely to crack unless damaged.

There are two types of safety glass in use; Laminated and Toughened.
Laminated glass is two layers laminated with a plastic film between. It can be made with either Annealed or Toughened glass. I have never come across Laminated & Toughened so you can be fairly sure most laminated glass is actually two layers of Annealed glass. This compounds the problem as it increases the likely hood of a temperature difference not only across the pane but also between the two layers of glass. The panes may try to expand and different rates increasing the risk of thermal stress fractures. So it is called safety glass because it holds together in the event of breaking or cracking not because it is less likely to break. It is in fact more likely to suffer from thermal stress.

So before you install any graphics, vinyl or film on glass it is good to know what sort of glass you are dealing with and either adjust to a material which absorbs little heat or warn the customer that if they demand a particular treatment or colour then the risk of stress fracture propagation is a possibility.
Before I install window film onto glass I undertake a glass survey which takes into account type, thickness and size of the pane, orientation, Shading from buildings or trees and even height above sea level. Each film I use has technical specs which give its Absorption, reflection and transmission values of Solar energy. Some of the less reflective, darker films may have an absorption value of more than 40% and these should not be used on larger annealed glass (& laminated). If a film has a high absorption factor then I must submit the details of the survey to the film manufacturer who will then decide if the installation is safe or not. All window film manufacturers will provide what we call a Film To Glass Application Checklist to help make these decisions. This is therfore an every day problem that we deal with installing film so know what to look for and the system we use helps deal with it. On most occaisions we are able to adjust the film to suit the situation but from time to time we have to warn the customer that we can not guarantee that thermal stress won’t happen and the installation is their responsibility.

So now to vinyl. It seems that many sign makers install to glass without this background knowledge and also we are not given the absorption figures of every type and colour we use, Therefore it is hard to make an assessment of each installation and we are down to guesswork and a few general guidelines.
Generally it is known to try and avoid dark colours (which absorb more heat) on annealed glass (and laminated), especially if it faces the sun at any time during the day. Try and avoid having large areas of glass covered by vinyl and other areas with no covering. Try and avoid the edge of a piece of dark vinyl running from an area of the pane exposed to the sun into an area in the shade. This is most especially important first thing in the morning when parts of the glass may be cold from overnight temperatures and others heat up quickly under the initial rays.

Your particular cases. The 3m x 3m pane is a large piece of glass and prone to spontaneous cracks. If it is laminated safety glass the problem is increased and adding a dark vinyl could also increase the risk. The risk is probably highest just after installation and is probably down to the crack already being there and just needed an little extra to make it happen. Is it your fault? Well possibly, but it is difficult to prove because the crack was probably there before you installed the graphic and could have happened anyway. Film manufacturers would look at the broken pane and can tell from inspection how and when the crack formed. As Vinyl installers we do not have the luxury of this testing service so can only warn in advance when we think thermal stress is possible.
The second situation you mention may also be a contender for increased stress due to the bottom strip. You do not mention if this was a dark vinyl or not and I can only guess that the glass was laminated.
The frost application does not immediately ring any alarm bells as frost is usually light in colour and not absorb much heat. However as the glass was already coloured that in itself may have caused a heat build up which only a small amount of extra from the vinyl pushed over the edge. I do not usually worry about installing frost on any type of glass but you have now drawn attention that smoked glass may be a worry.

A bit long winded but hope it helps with understanding the problems with glass and what to look out for.
If in doubt warn the customer in advance.

[Gert du Preez]

Stuart,

thanks, Mate! 😀

I basically thought along the same lines as you did. Now for question time again:

RE: Black on a window – if the vinyl is applied to the inside, it does not leave a "matt" or high -absorption face to the sun. In my own office I have blocked out some windows on ordinary float glass. No probs!

The second job mentioned is the exact same windows as the first. We printed magenta on clear, backed with white, and applied from the inside. The strip is narrow – maybe 20cm. ( from memory.) Both Laminated glass.

I never experienced this in Windhoek, where there are much higher day temperatures, and much colder at night.

Maybe I should print out your reply, and make the clients sign a disclaimer!

I must add that we do lots of frosted vinyl – we use between 1 and 3 big rolls per month. Lets call it 1000 square metres per year. This is the first time we had issues on frosted. So not at all a common problem on the frosted, at least.

Will Google some and look for more answers.

[Stuart Miller]

Hi Gert
The black will still absorb heat if on the inside. In fact could cause a higher stress than if on the outside as the outside face temp could be a larger difference than the inside face. Laminated glass even more so as the two layers of glass and middle film layer would cause uneven temp gradients.
Matt or gloss is no different, it’s the absorption factor of the material. For window film the thing that makes the difference is a metal in the film which reflects solar energy rather than absorb it. In the case of a reflective mirror film we may well install on the outside to reduce the solar energy going through the glass but a material which absorbs the energy can cause problems inside or out.

Many people use film and vinyl on annealed glass without a problem, you can not compare one situation with another, we can only understand that problems are possible and try and reduce the risk as much as possible. It is a bit of bad luck if it happens. It depends if the thermal stress in a particular area on the glass coincides with a crack which is just waiting to propagate. Many factors contribute to this so often you can get away with it, but knowing that it can happen and why helps to avoid the possibility.
The white backed magenta vinyl would probably absorb less than a black vinyl as it would reflect a little more but can’t tell absorbtion rates without a tested specification which is not possible with vinyl. I have some window films which let light pass through it and have some metal to reflect solar rays but still come up with a high absorbtion rate so could not be used internally on Laminated glass.

The frost, as you say, is not usually something I would ever worry about.

Just to give few absorption figures from my window film charts.
All installed to the interior of glass panes
Black Opaque Film 95% on 4mm single glass, 89% on 4mm double glazed.
White Opaque film 34% on 4mm single pane, 44% on 4mm double glazing.
Clear Frost film 22% on 4mm single pane, 30% on 4mm double pane.
These figures are unique to a particular manufacturers film so it is not possible to say what vinyl figures are but just show how different various colours can be.

Warnings start to be taken if absorbtion goes above 35% and 45% is probably the limit we dare install up to on annealed or laminated. Above 35% I always get confirmation of the install from the film manufacturer.

Looking at this even a frost film does absorb some energy and although highly unlikely it could in combination with a cracked, tinted, laminated pane push that crack to propogate.

[Shane Drew]

a glazier client tells me that a lot of cracking in glass that has been coated is because the glass is too tight in the frame, or has no room for extra expansion that is created when film coating is applied to glass.

If it absorbs a lot of heat, and the pane of glass is really tight in the frame, it will likely crack.

We do a lot of blacks and whites on glass that he later installs. We’ve never had a problem, but he makes sure there is enough room for extra expansion when he installs filmed glass.