Keep in mind whatever coating you use that takes a blasting of gravel is sacrificial and will need to be easily reapplied over time without special equipment. You want something that looks good when reapplied.
Gravel Guard Grey Undercoating | Chemicar
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Check out Gravel Guard and Total Coat.
I use Total Coat with a 2" thick nap roller. Looks gray out of the bottle, dries black. Washes up with water, after it dries it takes a high speed with a red 3m pad to get off.
https://4flhxg43fhbx1lzagh2ff8yq-wpe...hd_coating.pdf
Guy at work used gravel guard on is J**p. It is rated to take 500 hrs of GM9508P.
US distro is in Memphis TN.
Test for Gravelometer test GM9508p
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