Tom, this doesn't add up so well. The moss, especially if it is
green colored is due to the sun not shining on the porch or some
other condition that doesn't allow the surface to dry out. If the
top of the porch was only bricks and mortar laying on soil, it
would have disintegrated years ago. The only way the bricks could
be there is with a full concrete bed under them. You may have
other issues, but you're off to a bad start. If the bricks and
mortar are in petty good condition it can be sealed with a Silane
or siloxane masonry type sealer, but you've said you need to
repair mortar so I don't think this is your condition. The best
permanent cure probably will be concrete. If you want to just get
by for a while, you might try topping the brick work with a
topping cement like Mapei Planipatch or similar.
Keep the whole world singing . . . .
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