Parge

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.

A better method for dealing with efflorescence on masonry is to coat the offending surface with a parge coat of plaster. This is a plaster material that is slightly softer and more porous than the masonry. As the moisture flows through the masonry, it continues through the parge coat and evaporates from the surface, but the salts remain behind in the parge coat.

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.

You can waterproof by parging, coating with a commercial sealer, or both. […] Parging is a thin cement-sand plaster that you apply to the block. Allow the block to cure at least three days before parging.