Info on Stucco and Plastering-June, 2020-sixtieth issue
Dead crumbly mortar ---
Mortar cracked easily and turned to dust when you crush it between your fingers.
Mortar will turn to mush
When it dries before it sets.
For example, mortar put on thin on a hot day.
Mortar should never be retempered
When it is chunky.
This is a large cause
Of dead mortar, that is, mortar that doesn't harden.
Retempering is adding water and mixing mortar after it starts to set up.
This is probably what
Happened, mortar being put
On after it started to set.
Another large cause of dead mortar is mortar that has been dry mixed, and not mixed with water for a long time.
This happens using masonry sand. Dry mixed mortar will last only if made with silica sand, that is, crushed quartz from a factory
that has been kiln dried. We use this sand for our finish coat with white portland, and this mortar can be dry mixed
and stored for a long time. Silica sand is also used for glass making, so the sand must be dry. Also, silica sand is used for sandblasting.
Wet sand will clump up in the sand blasting pot.
Almost all masonry sand is wet, even though it doesn't appear wet. Dry mixed mortar should never be kept overnight, but thrown away.
Dry mixed mortar will go dead is as little as 4 hours in the summer.
Retempering cement mortar can be done before mortar is real firm, however it does lose some strength.
Interior Plaster can never be retempered, and must be thrown away. If one crushes it up and puts plaster on the wall, it
will turn to mush, I promise.