Spray Hard Coat Glass Vs CVD Hard Coat Glass


If somebody tries to sell you cheap reflective glass saying it is “Hard Coated”, the first thing you should ask is “Is it spray hard coat or CVD hard coat?”. Spray hard coat could be termed as a primitive and is relatively cheaper, in this one the chemical composition is sprayed over glass which would be in a semi solid stage (online process). Most cases, the coating tends to be uneven and deposition rate would be poor. In most cases the coated side appears yellowish.

CVD (Chemical vapor deposition in atmospheric pressure) on the other hand is far superior and the latest. Here, the chemical composition is vaporised and then allowed to deposit on semi-solid glass (online coating) in a controlled manner, achieving high deposition rate and the coating would be even. In most cases, the coated side would have a silver appearance.

It would be a disaster if spray coated glasses which come at cheap rates are used (especially when it is mis-sold with the name “Hard coated reflective glass”) in buildings. Below are some pictures for reference.

Spray Hard Coat – Coating peel off

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Designing Safely With Glass

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Here’s an interesting article by Rick De La Guardia on how to design safely with glass for today’s threats. This article was featured in US Glass Magazine. (Click on the article image to read more and download the entire edition)

Insulated Glass Units

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Insulated glass unit (IGU), also known as Double glazed unit (DGU) consists of two glass panes separated by dry air with an aluminum spacer. IGU has been in use in many countries since 1960s, except in the middle-east and Asia, … Continue reading

Hard Coated Reflective Glass


Espace rolin fortis, Brussels- Stopsol Silverlight

Hard coated or pyrolytic coated reflective glasses are those in which the coating is applied when the glass is manufactured,i.e. it is an online coating process. In this process of coating, the glass is fused into the glass at 650-700 degree celcius, and on cooling, the coating becomes a part of the glass.

Primary advantage of hard coated glass is the durability, it could also be handled like normal/annealed glass, could be easily heat strengthened, toughened, laminated or curved. These glasses could also be used in single glazing without any fear of losing the coating. Soft coat glasses (to be discussed in the next post) are susceptible to scratch and degradation over time, and requires special handling, hard coated glasses were invented just to counter this problem. Only disadvantage is the variety of colors available when compared to off line coating. Continue reading

What is a Green Building ?

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For all “Green-illiterates” (pardon my word usage)- A Green Building is not a green colored building, nor does it look different from any other building, then what is a green building?

A green building is basically distinguished with the approach, which involves the sincere care for the life of natural resources, providing human comfort, safety, as well as productivity. In a green building,

  • There would be minimum disturbance to the landscape and site condition.
  • Eco-friendly and recycled building materials are used.
  • Materials used are non-toxic and recyclable.
  • Equipments used are energy efficient and eco-friendly
  • Renewable energy is used

Even though the benefits of a green building are infinite, both tangible and intangible, an immediate tangible aspect could be readily observed once the green building starts operating, which is the significant reduction in operating cost and water costs (up to 40% savings !). Another tangible aspect would be the enhanced asset value. Intangible aspects would include increased productivity, health and safety, and much more.

Non-Solar Heat Control Glasses

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Solar and Non-solar heat transfer- IGU

In the previous post, types of heat entering a building was discussed, of which solar heat comprises around 80% and the rest is non-solar heat. It becomes very important to control non-solar heat as well even though it contribute to only 20% heat entering a building, especially in buildings where there is 24 x 7 operations and households, so as to bring down the energy consumption during night time. In this post, non-solar heat and how all to control it will be discussed in detail.

Non-solar heat is mainly transferred in three ways- conduction, convection and radiation, and is measured in terms of U-value (W/m2.K). Continue reading

Solar and Heat Control Glasses

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solar and non-solar heat

Glass is used in a building to harvest natural light inside it and there by reducing the internal artificial lighting requirements, in turn saving energy. The two major sources for heat entering the building is solar heat and non-solar heat; solar heat is nothing but the direct solar heat entering the building through visible light, non solar heat is caused by various factors like conduction, convection and radiation. Out of the heat sources, solar heat is the major one and requires more attention, even though the effects of non-solar heat could not be ignored as well, as it plays a major role in certain structures. Continue reading

Thermal Breakage in Glass


There are many instances where the glass panes in a building tends to crack for itself. This could be attributed to various factors like poor quality glazing, but there is also another factor which causes such breakage and is called thermal breakage. Thermal breakage in glass mainly happens due to the high difference in temperature between two points in a single glass pane, resulting in expansion and contraction in the same pane.

The temperature difference as mentioned above could be a result of many factors, such as difference of temperature between inside and outside, solar intensity in the region where building is located, type of glass (whether it is tinted, reflective, etc.), thickness of the glass, internal ventilation, type of glazing done, partial shade on glass, etc. Of all these factors, solar intensity plays a major role and it differs with geographical location, building orientation, seasons, etc. Continue reading

Optical Distortion in Tempered or Toughened Glass


In my previous post on Glass Tempering or Toughening Process, I had mentioned how the process is executed and the physics involved (Refer Back). Also a brief mention how the toughened glass quality is assessed after it breaks, this is very important because safety is the reason for we spend on tempering. There are also other issues in terms of quality when glass is tempered. These are mainly optical distortion, roller marks, waviness and bend, edge strength, coating burns, fragmenting, burns, spontaneous breakage, etc.

High Optical Distortion

Quality of tempered glass mainly depends on the quality of equipments used and the quality control procedures adopted. Optical Distortion , is mainly a blurred appearance in images when seen through the glass, as well as on the reflection on the glass. This quality issue in tempered glass is common to all types of glasses. Even though minor levels of optical distortion is present in most of the tempered glasses, but it gets magnified when the quality is that poor and the glass is applied on high rise building facades. The minor level optical distortion is inherent on tempered glass, considering the fact that glass nearly reaches it’s softening point as it is heated up to a temperature of 726 degrees, and also the fact that this glass moves in rollers, therefore it is also called roller wave distortions. Such distortions could be easily identified in reflective and low-e coated glasses. Roller wave distortions could be easily controlled by adopting suitable technology and quality control procedures (use of forced convection furnaces instead of radiation furnaces). Continue reading

Laminated Glass: Myths and Facts


There are major defects happening with laminated glass, if the process is not executed properly. Most prominent of such problems is de-lamination. This happens mainly due to the poor bonding between the glass and PVB sheet. In my previous post on laminated glass basics, I had mentioned about the clean facility requirement for lamination process, if this is not followed in the facility, there are chances for dust to stick on to the PVB and at a later stage, resulting in de-lamination. Waviness in the glass is also another reason for de-lamination: waviness in the glass can happen mainly due to poor quality tempering and even in annealed glass which has high amount of  inherent waviness. De-lamination mainly occur at the edges where chemical bonding is weaker. De-lamination may also happen when the unit is over exposed to water, mason errors (like improper cutting), applying poor quality sealants, etc. Continue reading

Laminated Glass Basics

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Laminated glass is made by sandwiching Poly vinyl butryl (PVB) sheet in between two pieces of glass. Laminated glass offers more safety because when the glass breaks, it keeps sticking on to the PVB sheet in the middle. Apart from … Continue reading

Glass Tempering or Toughening Process

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Annealed float glass when breaks is a safety hazard, just because it breaks into sharp pieces and can injure. Imagine, if an annealed glass applied to a window in the 6th floor of a building, and if it breaks by … Continue reading

What is Float Glass?

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Initially, window glasses were made by cutting from large discs of Crown glass. Crown glass is nothing but a large globe of glass, made by blowing molten glass into a crown or a hollow globe. The crown glass is further reheated and spinned out of the globe into large discs, which were then flattened using centrifugal force. These glasses were then cut into desired sizes. There were other methods of making glass as well, like the blown plate, broad sheet, polished plate and cylinder blown sheets, which were all in practice up till the end of the 19th century. 20th century witnessed more advanced processes like rolled plate, machine drawn cylinder sheet, flat drawn sheet, single and twin ground polished plate and float glass. Continue reading

A Glass Is a Glass Is Not Just a Glass!!!

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To be honest, my exposure to glass and glazing industry is brief, and the same was my knowledge about glass. Glass never had more than a decorative value in my mind, as it had to be for me since I was from a decorative product segment (paints). It was just after I got inducted into this industry that I had to invent this statement- “A Glass is a Glass is not just a Glass!!!”.

At first, I realized that there are different types of glasses being manufactured, each with different chemical properties and functions. But I could superficially assimilate the knowledge and as a new comer, it was enough for me to classify them as Soda-lime glass, lead glass, borosilicate glass and glass fibre. Since I’m only concerned with glass as a building material, I would be writing only about flat glass. Flat glass industry includes both float glass and sheet glass manufacturers. Basic difference between these two are the process by which they are made. Sheet glass is made by using iron rolling pins to flatten the molten glass and to get it into desired shape, and further grind and polish it to make it clear. Float glass on the other hand is flattened by making the molten glass to float over molten tin. I also learned that the float glass manufacturing process was invented by Alastair Pilkington and Kenneth Bickerstaff in 1957. Continue reading