Family-owned chimney repair serving Merrimac

A thin mortar top that crumbles at the edges

Some chimney tops are not a formed crown at all. They are a layer of mortar troweled over the top course and thinned out to almost nothing at the edges. BIA guidance says feathering a cast cap to the edge should be avoided, because it cuts the thickness at the edge and raises the potential for deterioration.

The thin edge is where these tops break up. Pieces chip away, cracks open and the top course of brick is left exposed to every rain. Without an overhang, water that does run off tends to run down the faces as well.

Patching a feathered top with more thin mortar repeats the mistake. The lasting repair is a new cap with a proper shape, thickened at the sides and overhanging the faces, which BIA says reduces the potential for water penetration, and sloped as the code requires. For your Merrimac home, the estimate describes that shape and its materials, so you know it is not another thin layer.

What a rain cap does and what it cannot do

A rain cap sits over the flue outlet and keeps rain and debris from dropping straight down the lining. That spares the damper, the smoke chamber and the firebox from water that would otherwise run down inside.

Three details matter when one is chosen. On a masonry chimney, the Florida Building Code sets the open area under a rain cap at no less than four times the area of the flue outlet it serves. BIA guidance says to get the maker's information on how a manufactured rain cap affects gas flow, and it says a metal cap should be corrosion resistant. A cap that restricts the outlet, or one that rusts, trades one problem for another.

What a rain cap cannot do is protect the crown around it. Rain hitting a cracked crown still soaks into the masonry, cap or no cap. Our chimney cap replacement service fits the cap itself, and when the crown underneath is failing, your Merrimac estimate says so on a separate line.

White deposits on the brick

A white, powdery film on chimney brick is likely efflorescence. BIA guidance explains that it needs three conditions at the same time, and it forms when water carrying dissolved salts reaches the surface and evaporates, leaving the salts behind.

Those salts show on the brick but usually come from what touches it, such as mortar, concrete or soil. That makes efflorescence a water sign more than a brick defect, and BIA notes it is usually not harmful to the brick itself.

Cleaning comes last. BIA guidance says to identify and correct the source of water and let the brickwork dry before cleaning recurring efflorescence, and light deposits can be removed by dry brushing or with a stiff fiber brush and water. On the estimate, the water repair comes first and any cleaning follows it.

• Soluble salts in or touching the brickwork
• Water in contact with them long enough to dissolve them
• A path through the masonry to a surface where water can evaporate

Film coatings that hold moisture in the brick

Some coatings sit on top of brick as a continuous film. BIA guidance on coatings explains that a film keeps water out from the outside but also inhibits the evaporation of water already inside the masonry, which can lead to clouding and spalling if the source of moisture is not addressed. BIA maintenance guidance goes further and says film-forming coatings should not be applied to exterior brickwork.

Salts make it worse. When water cannot pass out through a coating, dissolved salts can be left behind it, and as they crystallize they can grow enough to break the face of the brick. The coating that looked like protection ends up holding the damage in.

If your chimney is already painted or sealed, the first question is where the water is coming from. Flaking faces and clouding under the film show where to look. Your Merrimac estimate puts the water repair ahead of any new coat and says whether the existing film is part of the problem.