How to Seal a Chimney Hole

Wait until the weather temperatures are above freezing. The new mortar you apply will not set and cure properly if temperatures are too low. If possible, wait until spring to do your repairs so that both the interior and exterior of the chimney are warm enough for the mortar to properly set.

Put on a pair of safety glasses and work gloves.

Clear out all of the old and crumbling mortar around the hole. Tap the old mortar out from between the brick joints using a masonry hammer and chisel. Remove all of the old mortar from the hole area so there are no jagged surfaces.

Mix the new mortar with water according to the product instructions. Combine the mortar and water in a wheelbarrow or a tub.

Fill a spray bottle with water. Spray the edges of the area you will patch. Moistening the edges of the brick joints will help the new mortar adhere better.

Scoop up some of the new mortar with your masonry trowel. Place the trowel directly below the chimney hole.

Push the mortar into the hole with your tuck pointing tool. Fill the area with mortar until the mortar level is even with the outer surface of the bricks. Try not to get mortar on the bricks.

Allow the mortar to dry for 30 minutes, then wipe away any excess mortar from the bricks with a rag.

Spray the area between the new mortar and the bricks with water. This will help prevent any new cracks or holes from forming due to the mortar drying too fast.