What is Coated Glass and Why Do We Care?PART ONE
Coated glass is very simply that...it is glass which has been literally coated with various metallic compounds that only permit specific portions of solar radiation to enter a building. This keeps the furniture and carpets from fading, helps with air conditioning and heating, and adds to the beauty of the entire building. You might say it is indeed quite critical to the overall performance of the building. Especially in certain parts of the world where very large structures are constructed in actual deserts where the temperature soars during the day.
If we look closer at coated glass we learn that it is a rather finely tuned masterpiece of metallic compounds. Which are sprayed on when the glass is moving down the bath of molten tin, or evaporated on in a vacuum. So the coatings are either pyrolytic (made in fire), or vacuum sputtered. Either way they are Low-E. The E stands for the word emmisivity. Which means that only certain parts of the suns light are emitted or we might say "permitted" to enter. It is also true that these coatings are extremely thin. Hundreds of times less than the thickness of a human hair. Which means it wouldn't take much to waste them. That is why we care. Can you imagine the loss, if a very large building couldn't keep itself cool anymore? Or just simply the beauty of the building were in some way seriously marred? Please check out the GANA Glass Information Bulletin "Proper Procedures for Cleaning Architectural Glass Products". GANA 01-0116 It plainly states that, "...glass products can be permanently damaged if infrequently or improperly cleaned,...". Did you notice the word 'permanently'? When restoring plain glass surfaces whether clear or tinted (all the way through), we have much more than 40 nanometers to work with. A typical procedure for repairing glass surfaces can involve grinding with a silicon carbide technique;... and then polishing with cerium oxide. You can't 'grind' coated glass. Further, you have to be extremely careful when polishing it or using any type of chemical. Repairing Low-E surfaces is very limited. This is why we and our customers should care about the frequency and quality of the routine cleaning. GANA does specify in the bulletin cited here that metal razors should not be used during the routine cleaning of coated surfaces. Just soap, gently agitate with a soft mop, and squeegee off. Therefore when coated surfaces develop construction debris, or even pollution, which does not come off with the procedure described;...it is no longer 'routine cleaning'. Which means there is a potential of doing damage that could be permanent. It is suggested that various nonpermanent protective films be used at construction sites to protect the window surfaces during storage and when they are installed on the building. It is also suggested that the frequency of the routine cleaning be increased if pollution is more of a problem. I personally think it important to look for ways to check the integrity of such surfaces when they are being cleaned. Also when using water fed poles we should be looking at the silica content of the rinse, not just the TDS! Silica deposits begin invisibly and become more intense with repeated cleanings.