Q: How can we prevent double-wythe walls from blowing out when we fill the cavity between wythes with grout?

A: George Hanson, director of engineering for the Rocky Mountain Masonry Institute, says grout blowouts in double-wythe walls are most likely caused by:
  • Not enough ties
  • Ties not embedded enough
  • Grout placed too fast in one location
  • The vibrator left in one place too long

Space #9 wire ties no more than 24 inches longitudinally and no more than 16 inches vertically. For a double-wythe wall with a 2-inch cavity, embed the ties at least 2 5/8 inches in each wythe. In double-wythe walls, place grout in layers. Don't pump the grout in at one location and force it to run throughout the cavity. Move the vibrator continually; don't leave it in one place while you carry on a conversation or take a coffee break.