We have an old dryer vent that is no longer in use, but is still on the outside of the house. Due to some regrading, the vent is now below the ground line (but boxed off). This causes obvious problems when it rains heavily and often.

I was thinking of pulling the vent cap off and filling the most of the hole with spray foam, then after curing put an inch or so of mortar on the exterior edge. I'm not too worried about needing to undo this fix (I know the foam can be extremely difficult to remove...)

But I haven't used spray foam before so hoping to get some affirmation so I don't do something dumb.


  • 1
    Be prepared for it to expand a lot more than you think it will. And even when you think you've got it, it'll still expand more than you think it will ...
    – brhans
    Jul 30 '18 at 20:34

Nah. Build your new masonry exterior first, then if you need insulation spray foam from the inside. Foam breaks down over time with any sort of exposure.

  • I agree. Even at an inch think you still have something fragile. Even if your masonry skills are weak, slopping together an actual brick wall where the brick wall used to be is the best approach.
    – isherwood
    Jul 30 '18 at 21:00

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