parge

A coat of cement mortar on the face of rough masonry, the earth side of foundation and basement walls.

I watch as the mason at the Gilbert house picks up a glob of parge coat on his trowel. He smooths it on, moving from the bottom of the wall to the top. Next, he drapes a white fiberglass mesh from the top of the wall to the bottom and pushes it into the parge coat with his trowel.

Parging is a single layer of mortar applied directly to the wall with a trowel so that it covers the entire surface. Parges generally are rough and cover the whole masonry surface, but at times they are only applied to the joints or recessed portions of the stonework. Parges might subsequently be whitewashed for a more refined appearance, or used later as the scratch coat for stucco.

To apply a parge on to a surface.

If your smoke chamber [of a fireplace] is very oddly shaped or virtually impossible to parge, you can solve this problem using expanded metal lath. […] Once you have parged the sides and back of the smoke chamber, set the lintel in a bed of mortar and brick up the breast (front).

When more than one unit thick of brick or tile is used in the wall, the back of the face brick or tile may be covered with mortar. This parging will substantially increase the waterproofing of the wall. Basement walls usually are parged.