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.