I recently laid a brick step as a transition from one part of an old patio,
to a new, lower level patio. Both the old and new patios were stained and
sealed with a xylene base sealer about 3 months before I built the step.
Now certain areas of the lower concrete surface have developed white stains
up against the brick step. I do not think the clouding is coming from
moisture seeping in from below, as we did put a vapor barrier under the new
slab. I am assuming that it is efflourescence from the brick, because it
started immediately after we laid the step.

It looks as though I will have to strip the sealer from the effected patio
surface and re-seal it. How can I tell when the brick step has stopped the
staining? I would hate to go through the effort of re-sealing the patio,
just to have it cloud up again. Is there any way to salvage the existing
sealer instead of stripping it and starting from scratch?

TIA for help.