Acrylic vs Silicone In Ponded Areas

Posted: 06/10/2019

Let’s be very clear before we get started.  We do not advocate installing any coating product in ponded areas.  The NRCA defines ponding as any water that remains on the roof for longer than 24 hours following a rain.  Furthermore, there are very definitive best practices for any coatings project and they are:

1. Coatings alone will not fix a leaky roof

2. The existing roofing system must be repaired with like materials before applying a coating

3. Moisture trapped below a coating will try to get out through the coating

4. Coatings don’t stick to everything

5. Coatings do not work well on a gravel-surfaced roof

6. Coatings do not stick to a dirty surface

7. Spray-apply coatings

8. Review formal specifications

Check out our Fluid Applied Roofing Systems brochure to learn more about the eight best practices.

While you are there scroll down to page 5 where it describes our three coatings lines. Here is a snapshot of a portion of that page:

Look closely at the arrows above.  As I stated before, we do not advocate installing coatings in ponded areas.  However, we do say that Silicone Coatings will perform better in ponding situations than Acrylic Coatings.  I know what you’re thinking, “Yeah, sure.  Talk’s cheap.  Show me some proof.”  You want proof?  Well, here you go.

Since August 2017, we have been running an “unofficial” lab test of silicone and acrylic coatings.  Kind of like our very own “Redneck Mythbusters.”  In one of the samples, we divided a 2’ by 4’ box into two sections.  We sealed the corners as per our coatings specifications and then applied Acrylic Coating in one side and Silicone Coating in the other.  We added water to both sides and then monitored what happened with time lapse photography.  If things got dry, we added equal amounts of water to both sides to always keep the systems under the same amount of water.  We did this for about 3 months and discovered that things really didn’t change much.  So we removed the cameras and basically just left the samples exposed to the weather.  We didn’t add any more water other than what Mother Nature deposited at her leisure. 

After about 12 months, we began to see a change. The water levels were no longer equal.  There was more water in the silicone side than the acrylic side.  As time progressed, the difference in water depth became very significant.  Where did all of the water go from the Acrylic coated side?  We believe it passed through the coating and entered the substrate below because we see degradation of the wooden box frame below the Acrylic Coating.

It wasn’t a scientific study.  I don’t have a summary report that would cure most cases of insomnia.  I could bore you with the technical reasons why the Acrylic Coating performed as it did, but I won’t.  The simple fact about our little “experiment” is that silicone does better in ponding than Acrylic.  I hope this is enough proof for you.


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