Q.: A spandrel beam on the front face of a two-year-old shopping center is not plumb. The beam is 4 to 5 feet wide and 50 feet long. Some time ago it was given a patch that varied in thickness from 1 inch at the top to nothing at the bottom. The patch includes some metal lath. Water has made its way into the patch and caused corrosion and much of the patch has sheared off.
We must repair the beam again. There are no shotcrete operators in our area. Should we use a latex bonding agent? Should we featheredge? Should we apply a curing compound? The repaired beam will finally be painted.
A.: We suggest that you prepare the surface well by acid etching by recommended procedures including thorough rinsing. Then scrub in a 1:1 cement-sand grout made to a creamy consistency. Immediately, before the grout can dry, apply a portland cement plaster mix containing a latex. There are proprietary mixes of this kind on the market known as finishing mixes. This mix should trowel readily and doesn't necessarily need a curing compound, though a curing compound should help. At some appropriate point in this work you should investigate all the joints above the spandrel beam. One or more must be leaking and any leaking joints should be resealed. The joint above the beam should preferably be flashed using a flashing with an unobtrusive drip ledge.