Exterior Foundation Cracks

First, walk around the building and air seal any visible holes/cracks/gaps, etc. in the foundation or in the trim around the windows and doors. Look for gaps also around wires and pipes, light fixtures, fans, etc.  Anything that goes all the way through the wall. Trying to seal all the gaps that you may find between adjacent clapboards is beyond the scope of the task, but the homeowner should be told, so they can have these caulked.

If the area is at all dirty, clean it off first with a brush or vacuum.  If it's really crumbly, then ideally, you should use latex paint first to create a surface that caulk can stick to.  If you don't have a paint brush or paint to do this, you could tell your volunteers about this possible step.

If the foundation crack is big enough for the nozzle of the spray foam to fit inside of it, then seal it with the spray foam.  If it’s smaller, then seal it with the caulking.

Regular Great Stuff brand spray foam expands 300% after 20 minutes, so don’t spray too much.  It will puff out and look like some sort of overgrown fungus. This will displease the home owner. (Minimally expanding foam is also available.) Once completely dry, it can be cut flush and cleaned up with a fine saw, razor blade, and sandpaper, then painted.

When working with spray foam, make sure the volunteers wear protective eyewear at all times because if that stuff dripped down and got in someone’s eyes it would be disastrous.  They also have to wear gloves and should wear a respirator if exposure is long or they are in a tight, unventilated space.

If the spray foam gets on clothing or hair, don’t touch it ‘til it dries, because it just smears everywhere.  After it’s dry, you can cut it off easily.  If it gets on the hands you can use acetone to get it off, but some people are sensitive to this solvent.

Use the latex/silicone caulk in areas where the caulking might get painted.  Use the pure silicone caulk in areas outside where it won’t get painted.  Don’t use the silicone inside.