Ask the Expert Question-and-Answer Archive

by Ron Joseph

August, 2003

Non-Atomized Sprayer and Silicone

Q. I have a block building and need to clean and water seal it. I have had many companies come and put test patches on the building and have a good idea what will work. The problem is they say to apply the cleaner and sealer with a non atomizing sprayer such as a pump up garden type sprayer. This will take me a month to do. I wanted to purchase or rent a comercial type sprayer but can not find a nonatomizing sprayer. Do you know what we should use?

A. It is possible that you have been advised not to use an atomized sprayer because the sealer might contain silicone. If it does, then you do not want to apply it by any atomizing method because silicone is incompatible with paints. If even the smallest silicone particles become airborne they can travel long distances and settle on yours and your neighbors' cars, houses, etc. Once silicone settles on a surface it is extremely difficult to remove. When you try to apply a paint over it the paint forms craters and very little can be done to solve the problem. This can apply to you, just as it can to your neighbors, and it is definitely the potential cause of a large law suite.

I cannot think of another good reason for not using an atomized sprayer, but perhaps you can check with those who have given the advice. Also, look at the label on the can of the sealer to see if it contains silicone.

A#2. The answer I sent you last week remains unchanged. Silanes and siloxanes are chemicals that contain the silicone atom. Based on my understanding of these products their surface tensions are similar to those of silicone. Specifically because of their surface tensions they are water repellents you do not want them to deposit on surfaces that you might want to paint sometime in the future. You absolutely don't want aerosol droplets to deposit on automotive finishes or on glass, such as windshields. I have read some of the trade literature on these sealants and apparently you can use airless sprayers (spray guns) to apply them. Personally, I would be very cautious, because even airless spray guns atomize coatings and sealants, and the size of the droplets or particles depend on the pressure at which you are spraying. At low pressures, where the droplets are large, you will be safer than at high pressures where the droplets will be small. I hope this further clarifies the situation.