Is there a problem constructing masonry walls during rain? What problems can occur?
In general, I do not recommend building masonry walls during rain. In most cases, it is more cost-effective simply to call a rain day than to proceed with work during rain. Not only does worker productivity go down, but certain material problems also can occur. Concrete masonry units can absorb excessive water, which can result in higher-than-normal shrinkage later as the water evaporates. In clay brick with a low IRA, excessive moisture can reduce the IRA even further, which may make developing proper mortar bond difficult. Excessive moisture also can cause fresh mortar to wash out of joints and stain the unit faces. These stains may be difficult to remove, necessitating the use of chemical agents to clean the wall surfaces. However, masonry can be installed in the rain if the walls are covered under a temporary shelter and the materials are protected from rainwater. If walls are completed just before a rainstorm, protecting the top of the wall is important. The covering over the top of the wall should extend 2 feet down each face of the wall. The canvas or plastic used to cover the wall should be weighted down to prevent wind from getting underneath it and blowing it off the wall. Or special wire clips can be installed over the top of the plastic to hold it in place. Such wire clips are available from several manufacturers.