Simple Question. Which sealants will stand up to the high pH of Portland Cement as it cures over the course of a week? Cement is very alkaline! It can easily rise to a pH of 13. Over several days it can drop to 9. 7 is neutral. Below that is acidic. The higher the pH the stronger the concrete. If it drops to 6 or less cured concrete will visibly break up. Not good.
Now here is the interesting piece. As it cures it forms a rather strong bond to glass. Because of the chemistry. It is easy to push off within a couple days. Wait too long and you will be in deep muck!
Also hard water drops will rise to a pH of at least 9 (very alkaline) as they evaporate. Also as they evaporate the mineral salts will condense around the outer edge of each spot. Which causes the greatest pH there too. This means that the static stage two etch happens predominantly at the outer edge. Which is especially the case for dark tinted glass.
So. If we can identify which commercial sealant is most effective at resisting the highest pH of cement as it cures over at least a few days, than that should also prove to be the best sealant to use against hard water spots so they can be easily removed. But what kind of test should we use?
Testing Sealants Against Concrete. First if you would like to get deep into the chemistry of the hydration of cement check out this page. Cement Hydration This IGSA test is rather simple and quite eye opening.
First go out and buy a brand new mirror plate. If you have about four different sealants to test get a one by two foot mirror. Next polish the entire plate with a cerium oxide slurry and a sponge or felt pad with a square random oscillator of about 10,000 opms. That is oscillations per minute. This next picture I took from the Glass Smart FB.
It should take about thirty seconds per square foot to create a completely hydrophylic/water loving surface. Clean it off and check. Pure water should sheet over every square inch. Next divide it up into four 6 by 12 inch areas separated by some white "paint tape". Now apply four different product samples of sealants. Like The Invisible Shield, Nanovations NG1010, Aquapel, and another. There are many of them out there. I will NOT get into the chemistry of them. Because it really doesn't matter. What matters most is their performance. Let each sealant have enough time to cure. According to the instructions. And make sure that you apply each one correctly according to the instructions. When you are ready mix up some nice wet cement and put about three little plops on each of the sealants. Give your experiment at least several days for the cement to cure. Let it hydrate. Next remove all of the little cow paddies. Clean the entire mirror. Then run pure water over the entire plate. The area where the cement did not make contact should still bead water. Also the areas that did make contact with the cement should also bead water. If there are any areas that did make contact with the cement that have stopped beading water then you will know that those sealants have been chemically degraded by the high pH of the concrete/cement. And concrete would eventually lock onto those surfaces. It is also important to know where you applied which sealant products. To identify which sealants were not effective. If any sealants did not stand up to cement after only several days they most likely will not be very effective at standing up to hard water spots. The test I did many years ago was quite striking. It was very easy to identify the best sealants.
I will continue to work with this test. It is in my toolbox.
Please come over to the Glass Smart FB and join in the SMART discussions.
Henry
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