How to Caulk Under Sheetrock on Outside Walls

Measure the size of the gaps. Any gap over 1/2 inch calls for the use of expanding foam rather than caulk. If a gap is considerably large, as in over 3 inches, cover the gap with a small piece of drywall first. Any gap left over can be covered by caulking or expanding foam.

Prepare the caulk or expanding foam while wearing gloves. The expanding foam comes in a canister and has a nozzle on the end with a trigger. Caulk also comes in a caniste, but requires preparation before applying. Snip off the top of the plastic caulk canister at a 45-degree angle. To do so, use a utility knife or place the top of the plastic in the small hole at the bottom of your caulking gun and pull the gun’s trigger to slice off the plastic top. Slide the canister into the caulking gun with the plastic top pointing out.

Begin applying either the caulk or expanding foam to the gap. If you’re using caulk, HGTVRemodels advises holding the gun at a 45-degree angle and pulling the caulk toward your body when applying. Do not let the caulk sit in one place; apply an even amount across the entire gap. Smooth the caulk with your finger after applying the sealant. If you’re using expanding foam, place the plastic nozzle into the gap and begin applying the foam. Stop once the entire gap is filled.

Trim the foam with a utility knife once it fully dries. Depending on the manufacturer, the foam may take from under an hour to over 10 hours to dry.