Testing Sealants Against Alkali Attack

If you charge someone tens of thousands of dollars to remove hard water spots/stains from their windows you better be able to guarantee your work.  Because no one is going to want to spend even close to that kind of money every six months just to have clean windows.  We on the other hand don't want to spend a great amount of time just to keep them clean.  The best way to do this is to seal the glass surface.  But seal it with a product that will stand up to the ravages of the high pH of hard water drops.  We want the absolute best.  But how do we know which product IS the best!

pH resistance is not determined by whether the sealant is hydrophobic or hydrophylic.  It is true however that a water drop will attain its highest pH during the last few seconds before it completely evaporates.  This is because the water in the drop attains the greatest concentration of mineral salts around the outer edge of the water drop.  Just before the drop poofs away it becomes a water ring.  This is the reason the water spot is more of a spot ring.  If you study these pictures of different water spots you will see clearly what I mean.  The middle is a dry basin with very little mineral deposits.  When polishing the windows the most difficult part of the spot to remove is where the greatest concentration of minerals are.  That being the outer edge of the spot rings.  So a hydrophobic surface will encourage the formation of water spots.  Whereas a hydrophylic sealant will not.  It will cause the minerals to spread out evenly making it more easy to remove.  However if the hydrophobic sealant is much more resistant to pH attack then that would be the better sealant to use.  But if the hydrophylic sealant is even just close to being as resistant to pH attack, then that would be the better choice.

The best way to find the best sealant/product whether it be hydrophobic or hydrophylic is to put several of them to the test on the same plate of glass over the same amount of time.  So clear the window with a polishing system.  The bare glass should sheet over.  Glass is naturally hydrophylic.  It is only hydrophobic if it is contaminated with hydrocarbon or other hydrophobic residue.  Next tape off a number of squares.  Then apply the different products, one per square.  Wait six months and try to remove the newly formed mineral deposits/spots.  First with an applicator and squeegee.  Then with more aggressive methods such as 0000 steel wool.

Another way to test for the best sealant is to polish a brand new plate of glass.  This will make the glass totally hydrophylic.  It takes about 30 seconds per square foot.

Then seal the entire plate with a hydrophobic sealant.  After this apply a few splotches of fresh concrete.  It only takes a couple days for the concrete to harden.  During this time the pH of the concrete reaches 9 to 9.5.  Which is very high.  It will literally eat right through most sealants.  Next push off the concrete then run tap water over the glass.  If the concrete has eaten through the sealant you will see the water sheet over the glass only where the concrete was.  If not you will have discovered a high quality sealant that is resistant to alkali attack.  Test out the other sealants in the same way.  When you find the best hydrophobic sealant all you need to do is test it against whatever hydrophylic sealant you might have.  To do this just follow the instructions given for the first experiment.  Give it a good six months.  The maintenance cycle will depend on how big the building is.  Also how intense the stains are.  

These tests will give you the ability to offer a guarantee.  You will know exactly how much time it will take to remove the stains, and how much time it will take to keep them off.  The tests will also tell you exactly which sealant you want to use.  Although it still must be factored in I wouldn't care too much about the expense of the polishing compound or the sealant.  The greatest expense will be in the time.  Time is everything to us.  The time will determine the cost.

Written by Henry Grover Jr.

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