Coating a Rubber roof

I have a flat rubber roof about 500 s.f. I had a company put on a Silver Coating. What concerns me is the company sent 2 men. They carried up some old looking buckets & mops. They were done in lees than 1 hour. Could they have done a proper coating in this amount of time & have had enough material to cover the roof in those open buckets. I need to know before i pay the bill.
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Dell Inspiron
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A gallon of wall paint can cover about 400 square feet, so two 5 gallon can can potentially cover 500 sq feet, but not very thick.
What I can't tell you is if the material is going to do whatever you want it to do. I'm not familiar with Silver Coating.
If it is this stuff, you'd need three cans http://www.gardner-gibson.com/linedetails.aspx?idh
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Did they say the materials are compatible? T
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They were slow, one guy could have done it.
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