There are clear coats that can be applied that you will never know are
there. Mostly sold for porous bricks to prevent moisture transfer.
I can't recall any brand names but it will be sold where bricks are sold.
Yes, these products are well known based on polyethylene emulsions and are
used as anti-grafiti coatings. Often a high pressure hose has to be used to
remove the coating (and the graffiti with it).
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