I always tell people when they have a new problem the is sure there to
be a new cause...find this out first then fix the damaged areas. If
this is true "cinder block" (made out of cinders very rough almost
razor sharp texture) then I would skim coat the entire block
surface...all the way around the house outside...because cinder block
will just continue to disintegrate making the problem worse. if they
are concrete block if the outside was not coated which it sounds like
it was not anywhere you have dirt in contact with the soil the joints
are going to fail sooner than later. You can make up a "slury" of sand,
cemen, and bonding adheasivet and paint this on the blocks or trowel it
on (like a thin coat of stucco) to seal the entire area and the color
will remain grey like your concrete below. after that I would put the
paint on.....

wrote:
I have poured concrete basement with two rows of cinderblock at the
top. During the heavy wind driven rain the water starts to seep
through the mortar where cinderblocks connect with concrete. This
happens despite the fact that the level of connection is above the
ground by about 2 ft (exposed area of the basement wall above ground).

From the outside the level of connection is slightly visible as a
tiniest hairline crack. The crack stays wet on the outside after the
rains are gone for a couple of hours or so indicating it's more wet
than the rest of the wall.

How can I waterproof or seal the mortar (or that hairline crack) from
the outside so that the water does not seep through it?

What substance can I use? What color is that substance? (The house is
grey there.)

Thanks!