StructuralQ An inspection report on our home indicated there was evidence of past rodent infiltration. An engineering consulting firm recommended that, to prevent rodents from burrowing underneath the foundation, we have a contractor apply shotcrete across the entire crawlspace bottom, then have a 2 oz. (60 mL) vapor barrier installed on top of it. The barrier would be glued or taped up the sides of the crawlspace. As there is some shrinkage of the concrete during the curing process, I would expect creatures could later emerge between the shotcrete and crawlspace sides. Have you heard this type of shotcrete application in a crawlspace as a structural pest barrier? What thickness should the shotcrete be? Is this use of shotcrete effective? Are there any potential drawbacks to using shotcrete in this way, such as possible problems with the house later on?
Shotcrete is a method of placing concrete and the properties of shotcrete are equivalent to those of cast concrete. The type of work you are describing is done in many cases with the shotcrete process and is commonly called “ratproofing.” As you have engaged an engineer, we would suggest you follow his advice and he should determine the thickness required. Providing a row of dowels around the stem wall to tie the shotcrete to the wall should eliminate any significant separation between the shotcrete and the stem wall. Shrinkage of concrete between the walls may cause some minor hairline cracking, but nothing to allow ingress of rodents or insects.
