What should be done with a newly constructed masonry wall if it looks like rain?

When a newly constructed masonry wall is at risk of rain, covering it with canvas is the best practice to protect the wall from adverse weather conditions. Newly laid masonry, such as brick or block, requires time to cure properly. Rain can introduce moisture that might cause undermining of the mortar before it sets, leading to structural weaknesses, efflorescence, or other complications in the masonry.

Covering the wall with a protective canvas creates a barrier against the rain, ensuring the masonry remains dry and allowing the mortar to cure effectively. It prevents water from infiltrating the work, preserving the integrity and durability of the construction.

The other options, while they may appear to be protective measures, do not address the immediate need to prevent moisture damage from rain. Wetting down the wall could actually exacerbate the risk by making the mortar too wet or disrupting the curing process. Pargeing the top before the mortar has set may lead to adhesion problems or additional work if the rain washes the freshly applied material away. Taking the wall down is an extreme measure that would be unnecessary if protective methods, such as covering with canvas, are applied in advance.