Peter asks, “We have a fireplace and of course a resulting chimney. I have heard that brick chimneys require maintenance. My neighbor had some white stuff on his brick chimney. Is this something I should be concerned about?

It is officially summer time. That means afternoon rains that are wild enough to flood even the “tallest” places. Many people thing about waterproofing around windows and cracks, but what about the chimney? The chimney requires A LOT of maintenance, and sometimes is the most overlooked.

The technical term for that “white stuff” you mentioned is efflorescence.This is formed when water penetrates the brick chimney. It gets in the mortar and leaches out on to the surface. Thankfully for you, it is your neighbor that has the big problem, not you. But, if you let yours go you might be in the same situation. Chimneys require a lot of maintenance and care. They are up there taking the elements from all sides, with no protection from overhangs or roof coverings.

Masonry materials are very porous so they will absorb large amounts of water. Brick is like a sponge, absorbing water and wicking moisture to the chimney interior. Defective mortar joints or the use of improper mortar or brick can greatly increase the tendency to absorb and convey water to the interior of the masonry chimney structure.

Many products have been developed specifically for use as waterproofing agents on masonry chimneys. These repellants are vapor permeable which means that they allow the chimney to breathe out, but not allow water in. Thus water that has penetrated the chimney, or moisture that has originated from inside, is allowed to escape, while the waterproofing agent prevents water from entering from the outside.

Water repellent is applied to chimneys to protect the masonry chimney against deterioration from water penetration. Water repellent is not the same as a water sealer; water sealant can cost homeowners money because it traps water vapor inside the chimney. If this water vapor does not escape, it will condense, freeze and accelerate freeze/thaw damage. The water repellent that is applied does not trap water vapor, does not change the color of the chimney, and creates a photo-reactive process that allows the treated surface to repel water similar to the way two identical poles of magnet repel each other.

Paint, or any non vapor permeable water sealer, should never be used as a waterproofing agent because it will trap moisture inside the chimney, accelerating deterioration.