Asphalt roof - how much cleaning do I need to do?

I am getting ready to apply a new elastomeric roof coating on top of the existing asphalt membrane.
Instruction says to thoroughly clean and let dry before application. The problem is the asphalt membrane has a lot of "loose" particles the size of sand. I think it's part of the asphalt that is coming loose? I am unable to clean them off totally. I can brush and brush and brush and more come out and it seems to never end.
Any suggestions? May be I should just apply it as-is?
Thanks,
MC
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MiamiCuse writes:

New coating should be at least 3 times as thick as the largest loose particle.
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Just take a leaf blower to it. Be careful not to lift up any loose edges with the airstream.
aem sends....
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Thanks aem, I was using a push broom, and the more I pushed the more loose particles I got. So I didn't need to do all that? Oh well.
MC
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