How to Seal the Exterior of a Broken Down Chimney

Prepare a mixture of 1 tbsp. liquid dish soap and 1/2 gallon warm water in a plastic bucket. Stir the ingredients until they are well incorporated.

Slip on a pair of sturdy shoes, sturdy work gloves and safety goggles and grab the bucket and a plastic scrub brush before climbing a ladder to access the chimney. Do not attempt to repair or seal the chimney after any inclement weather or on a windy day.

Dampen the plastic scrub brush with the soapy mixture and thoroughly wash the surface of the chimney to remove any loose dirt, debris, efflorescence and chalking. Allow the chimney to dry completely before continuing.

Load a caulking gun with tube masonry cement. Pull the metal bar of the caulking gun and insert the masonry cement tube. Examine the chimney and repair any minor chips, cracks and damage by filling them with a healthy dose of the cement. Do not worry if you’ve added too much, as this is more advisable than skimping on the product. Allow the product to cure for at least 12 hours before continuing.

Apply a thin coating of silane sealant to the entire surface of the chimney with a paintbrush. The silane provides a breathable, water-resistant coating on the chimney that won’t alter its color. Allow the first coating to dry for at least 24 hours or according to the package directions before continuing.

Apply a second thin coating of the silane sealant with the paintbrush.