Brick Repair

The process we recommend in the proper maintenance of exterior brickwork is to do as little intervention as possible in regard to the pointing mortar if in fact the large majority is still intact. A mason should replace only what is missing wholly, or eroded back more than 3/8″, with fresh mortar, which will match very closely to the original mortar in composition, color, texture and tooling. The total repointing of a building is often unwarranted. Patch pointing is cost conservative as well as functionally superior than pointing the whole building in an incorrect manner. If total repointing is to be done because the majority of the mortar is past its useful service life, a mortar should never be applied that consists of a Portland cement and fine sand paste placed over the top of the existing joint. This technique employed by many masons is superficial because of a shallow depth which lacks a good mechanical key to the surrounding brickwork. Over time this “scrub joint”, as it is sometimes referred to, may delaminate. However, the extreme disservice that this technique brings is that the fine Portland cement, which will pass through a #200 sieve, (a sieve where even a water droplet is not able to pass through), allows the wetting and drying cycles of the building, (a cause of masonry unit and joint weathering), to occur through the brick or stone thus exacerbating its breakdown instead of more of the mortar joint. The mortar joint is meant to be more sacrificial than the irreplaceable masonry units. The “wicking-in” of water through the brick or stone can then can be driven further into the building by blowing rainwater and cause interior damage.
Category: Brick Repair

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The use of “sealers” on exterior historic masonry is a questionable intervention. Since all historic masonry walls, as well as the individual historic masonry units, need to “breathe”, (i.e. allow moisture vapor to escape), there should be a specific purpose in using some form of coating. Only after physical waterproofing via repointing and physical repair or damaged units should chemical “waterproofing” be considered. Those considered must have properties which maintain a high vapor transmission which will allow moisture to escape. The specific purposes to use a water repellent are:

  1. Inhibiting deterioration of the masonry units by not allowing the wetting/drying cycles, (the very cause of historic masonry failure over time), to occur through the unit or the joints. Although water repellents are not traditional historic material they can act as a “sacrificial barrier” to weather away from the action of the elements before more of the historic fabric weathers away.
  2. As a grain strengthener, (surface consolidant/water repellent).
  3. As an inhibitor to capillary action and the absorption of water into the building if the absorption of the brick is greater than the masonry’s ability to release the water back into the atmosphere before entering the building’s interior.

Overall great concern should be employed and testing should be carried out before simply spraying a building with a water repellent. In the turn of the last century masonry buildings were waxed for protection and sure enough the wax yellowed and picked up atmospheric pollutants which greatly discolored the building. Silicon sealers soon followed which yellowed if not simply breaking down from ultra-violet rays of the sun. Now silane and siloxane breathable water repellents are in vogue. These materials seem to be effective for some applications. The question remains as to whether the breathability of the historic fabric will in time be compromised. Our advice is to remain conservative and do not introduce chemicals to historic masonry just to do it as a final measure.

Category: Brick Repair

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If there is moisture present at the gable end of a brick or stone building and the roof system is working and the flashing system is working around any chimney’s that extend past the roof line, the moisture may be due to condensation. A column of air that exists, in used or unused and capped-off tight chimneys, moves the expanded air through a natural draw upward and the moisture content in the air may be condensed by change in pressure, (dew point), or thermal shock, (at the line where the air in the chimney goes through the roof). All masonry, wood and building materials have an “R” value which means “restriction” to airflow. So a cap that seals a chimney does restrict airflow but does not eliminate it. It takes approximately 11 inches of masonry to equal the “R” value in 1 inch of wood to demonstrate approximate value differential. Air which tries to move up and out but condenses near the top gets quickly absorbed into an unlined and capillary filled brick masonry units of the chimney. The plaster, the lime bedding mortar and soft salmon brick are highly absorptive.

The moisture problem is compounded when a high efficiency gas or oil heating system pumps out an exhaust, into an uncapped/unlined chimney, that is practically nothing but hot air full of moisture and some unburned impurities. Even in the case of a lined chimney, the liner itself should be insulated on the outside of the liner within the walls of the chimney. The “salmon” un-vitrified center of the brick exfoliates on to the floor in the attic as salt crystals, (efflorescence), build up under the “fired skin” of the brick. Salt build-up jacks out the face of the brick and even the continually building up “salt skins” to finally hollow out the brick faces. The moisture wants to move toward the inner warmer attic instead of the colder temperatures outside of the building. Unused chimneys should be filled with free-flowing vermiculite masonry fill insulation and capped off at the top. Liners should be cast-in-place lightweight concrete which is creosote/acids resistant and insulative, or lined with stainless steel with an insulative blanket or vermiculite placed around the outside of the liner with in the walls of the chimney chase. Unfortunately even non-rusting stainless steel liners may deteriorate in time by acids in creosote eating holes in the liner. The stainless option is less expensive at the front-end of installation. The poured-in-place type is an excellent long-term value if installed properly.

Category: Brick Repair

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