Bricks, Masonry, Asphalt and Concrete - concrete parging query

Lately, following a rain, I notice dark lines (plainly indicating moisture) in and behind the parging around our block foundation.

These "lines" coincide pefectly with the mortar lines in between each course of cinder block making up the basement / foundation to our house.

Eventually, say, several days after a heavy rain, and after everything else has dried off, the lines "disappear".

Are these lines anything to worry about?

Do they indicate the parging was placed on in too thin a coat?

I have used latex Drylock -- with tremendous success -- on the *interior* of block foundations and would be willing to do the same here -- even if for only cosmetic reasons.

TIA for any insight!

Masonry is not waterproof, only water resistant. Placing a thicker parging layer might even out the moisture absorption, but it actually sounds very normal. The mortar in the wall is more absorbent than the block and takes longer to release the moisture. Putting a sealer might help some if the only source of moisture is from rain falling against the wall. If you live in an area where the outside temperature falls below freezing trapping moisture in the coating can cause it to break up and separate from the substrate as the ice expands.

brickeyee,

thanks very much.

Yes, the only source of moisture is rainfall, subsequent ambient moisture, etc.

While reading your reply it occurred to me that I had sprayed some leftover clear concrete sealer (left over from sealing my sidewalks and back patio) on the exterior foundation walls last Spring / Summer.

And yes, it DOES definitely feeze 'round these parts (Southern Maryland).

I think I'll leave well enough alone, NOT use any DryLok or similar products on the exposed parging and just keep caulking any vertical cracks that appear, which is all that I've done with any previous houses / parging covered foundations.

Thanks again!