THE CARE & MAINTENANCE OF MASONARY CHIMNEYS

Proper care and maintenance of your masonry chimney and its various components is vital to insure that the chimney remain standing and secure from water infiltration for the life of the house. The key components of the chimney are bricks, mortar, clay flue liners, flue cap and base flashings. It is very important that timely repairs be made to these items to ensure that deterioration of the chimney does not occur. When needed repairs of the chimney are postponed or otherwise neglected, the consequences can be some or all of the following problems: stained wall coverings or plaster, rotted wood, rusted damper assemblies, deteriorated firebox assemblies, cracked clay liners, and partial or total collapse of the chimney walls.

PROBLEMS MASONRY CHIMNEYS FACE:

Rainwater washing over the mortar joints of the chimney over a period of time will erode mortar from between the bricks. Left unattended, the loss of mortar will result in the loosening of the brick, causing gaps between bricks that will allow water to penetrate into the walls of the chimney.

When water finds an opening in the chimney through a crack in the brick, mortar, crown or flues, it can accelerate the damage done to the chimney when it freezes. Trapped behind mortar joints, freezing water can push mortar from between the bricks. Brick, especially porous varieties, are prone to flaking during freeze/ thaw cycles. Over time, the face of the brick falls away, further accelerating the deterioration of the chimney.

The crown of the chimney is the portion of the stack at the very top of the chimney. It covers and seals the top of the chimney from the area between the clay flue liners and the outside edge of the chimney walls. Regardless of the material used for the crown, it is prone to decay and erosion due to exposure to the elements and periodic movement of both the chimney walls and clay flue liners as they expand and contract. Cracks in the crown and flues allow water to penetrate into the chimney, which causes deterioration to the chimney walls. Cracks may also allow water to leak into the house.

The area where the roof of the house is joined with the vertical walls of the chimney can be the source of many roof leaks. How these base flashings were installed will determine the degree of maintenance that is required. Metal base flashings that are firmly set into the wall require little maintenance, provided they aren’t rusted. Base flashings that are covered with plastic roof cement may require constant care.

A chimney flue without a flue cap is like a skylight without the glass. The opening of an average chimney flue is 96-144 square inches. Imagine the amount of water that pours through this hole each time it rains. It runs down the chimney and seeps into the bricks and mortar. The inside of the chimney stays wet long after the rain stops. This moisture erodes the mortar joints from the inside out and also weakens the brick. Add to this the many freeze/thaw cycles that it must endure, and you have all the ingredients necessary to severely damage your chimney.

If bricks and mortar deteriorate significantly, the integrity of the chimney is compromised. Walls that are missing bricks and mortar are prone to collapse partially or completely, depending upon the extent of deterioration. If the chimney falls it can cause further leakage into the building or structural damage.

Periodic inspections of your chimney by a knowledgeable contractor, is one of the best preventative measures you can take to protect yourself from water damage. Often, potential roof leaks can be discovered before they materialize. Regular maintenance of the chimney will prevent leakage and damage to the building’s interior.

REPAIR AND MAINTENANCE

Chimney walls with only a few deteriorated bricks are good candidates for partial brick replacement. In this case, the damaged brick is removed and replacement brick is fitted into place. Mortar joints are then tooled to match the mortar profile of the rest of the chimney.

Mortar joints that are still in place but have eroded can be restored through a process called “tuck-pointing”. Tuck-pointing is performed by cutting or grinding out the old mortar joint until sound mortar is found. The prepared joint is then filled with the proper type of mortar. The joint is then tooled to match the profile of the rest of the chimney. If the entire chimney is tuck-pointed, it is recommended that a concave shape be used, as this mortar profile provides the best resistance to the weather.

Replacing a cracked or broken chimney crown may be done in conjunction with other chimney repairs or alone if the rest of the chimney is intact. A well constructed crown should be made of stone or reinforced concrete and cut or formed to not only slope away from the chimney flues, but also to provide an overhang or drip edge, that projects past the walls of the chimney below. This drip edge directs the water runoff from the crown, away from the sides of the chimney, helping to prevent erosion of the mortar and damage to the bricks along the chimney’s vertical surfaces. Once the crown is in place, a flexible foam material is trimmed flush with the top of the crown and a sealant is applied around each flue.

Waterproofing underlayments, shingle tins, chimney saddles, reglet counter-flashings, step flashings and face flashings are all integral parts of the base of the chimney. When installed correctly, they combine to form an elegant system for draining water away from the chimney. If any of these are failing they can be removed and new ones properly installed.

Installation of chimney flue caps are an inexpensive, preventative measure that every homeowner can take advantage of to prevent rain, snow, and sleet from penetrating and damaging the chimney. A well- designed flue cap will also prevent animals and birds from entering and nesting in the chimney. It will also keep out leaves, and other debris that could lead to a blockage in the flue.

REBUILDING A CHIMNEY

Determining whether or not a chimney needs to be rebuilt partially or completely depends upon the extent of the deterioration of the chimney. If bricks and mortar have failed for only a few courses below the crown, and the remainder of the chimney is in sound condition, only the top portion of the chimney needs to be rebuilt. If these failed brick courses are near the base of the chimney, of if the mortar is completely missing from between the bricks over many areas of the chimney, the chimney will need to be rebuilt. If clay flue liners are cracked, broken, or have shifted down into the chimney, the chimney will need to be rebuilt to the level of the deteriorated flue liners

WATER REPELLENT

All mortar, and nearly all brick, are porous and will absorb water. When common bricks are exposed to the effects of rain and snow, absorbed water can cause the bricks to flake or crack and the mortar to deteriorate when the chimney walls freeze in the winter. Clear water repellent coatings applied to the surface of the brick have been found to reduce the amount of water absorbed by the brick masonry.

There are several products available that have been specially formulated to act as water repelling agents on masonry chimneys. These formulas are vapor permeable, allowing the chimney to expel moisture that may have gotten into the chimney walls, while at the same time repelling water from the outside entering the wall. It should be noted that paint or any non-vapor permeable water sealer should never be used as a water repellent because it will trap moisture inside the walls of the chimney, thereby accelerating deterioration. Furthermore, a water-repelling agent is not by itself a substitute for needed masonry repairs to the chimney.