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Should my brick building be completely repointed?
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.
Correct total repointing requires removing the joint to a depth of approximately 2-1/2 times its width and then using a compatible mortar in relation to the final p.s.i. and both the liquid and vapor transmission rate as that of the remaining joint and brick. High lime content pointing mortar is compatible with the soft and absorptive nature of historic brick which rely on their "fired skin" to protect themselves and the building from rain intrusion. If high concentrations of Portland cement were in the repointing mortar instead of lime, when moisture in the brick were to expand and contract during freeze/thaw cycles, often the unyielding mortar forces the softer face of the brick to exfoliate thus leaving a vulnerable unburned "salmon" center of the brick exposed to the elements.
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.
My bricks on the chimney in the attic are disintegrating. They have a white powder on them and they look like they need to be replaced. What caused this?
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.
I have other damp walls on my historic brick or stone building. What could be causing this?
Moisture that is seen in the masonry walls at first and second floor level when it has been determined that no plumbing is leaking within the wall, or improper pointing, flashing or cracks are apparent on the outside, may be due to various causes.
1. "Rising damp" originating from earth sloped toward the building instead graded to lead water away may sometimes absorb into the mortar or stucco. To correct this the grade should be sloped away from the building. Heat from the baseboard units pull the air containing water toward itself too. This is apparent when plaster crumbles near the baseboard of the first floor or above the baseboard heating unit. A full damproof course of low absorptive masonry such as terra cotta tile can be installed to arrest this condition. Below grade it has been a traditional building technique to parge coats of external plaster on the foundation and coat the parging with tallow, (animal fat). Dig down along that side of the house and after a parge coat of 1 part NHL 5 and 1 part sand apply a bituminous foundation coat to seal out moisture. Consider use of a sheet drain which leads to a french drain tile. Finally remember to grade away from the building and remove loose-fill that causes drainage against the building instead use a less percolating soil that allows water to be shed-off.
2. There are unused flues built directly into the thickness of solid brick or stone walls that need to be filled with vermiculite or if used, properly lined. Sometimes you will see an accelerated decay of the brick faces and joints where the hidden chimney within the wall is located. If a high efficiency heater is installed without a liner in these hidden chimneys you may see old creosote being carried through the brick or stone wall by the catalyst of condensed water from the efficient heater to the outside face of the wall. This often leaves a brownish streak coming down the wall. The correction is to properly line the chimney with insulative liner.
3. The moisture content in the room or an adjoining room/basement is great and requires proper ventilation. Often rooms in older houses are tightened up with thermal windows and further power-cooled. They should be equally power-ventilated and not rely on ridge, soffit, or unbalanced venting methods. Natural venting ports in basements are sometimes closed-off. This modification sometimes changes the dynamics of the original design for proper ventilation.
4. When north-east driving rains push against a wall which was recently repointed or re-stuccoed in Portland cement based material the result is often a water infiltration into the building's bedding mortar. You may see a "water-logged" look to the exterior masonry. The moisture gets caught up in the punky, loose and absorptive bedding mortar in the deep mass-masonry wall and can't get out. The answer is not to replace the bedding mortar. The answer is to re-repoint or remove and re-stucco the exterior with the correct lime/sand mortar and stucco so as to return to the appropriate breathability of the historic system.
Someone wants to sandblast my house. Should I let him sandblast ?
Invasive cleaning methods such as sandblasting or high-pressure washing should be a questionable intervention upon historic fabric of any kind and should be considered carefully. Quartzite sand should never be the medium used on historic brick whose frail "fired skin" will be destroyed and thus expose a porous "salmon" center. Never sandblast sand upon any stone with intricate carvings or upon a terra cotta unit whose glazing would be irreversibly removed. Other media is available such as ground up walnut shells, baking soda, diatomaceous clays, glass beads. Which media to be used is to be judged on their effectiveness using the most non-invasively method first. The non-invasive method is the one that works upon the historic substrate to lift only the undesirable contaminant. One could employ quartzite sand, (in varying gradation and at various p.s.i. pressure), when there is a sacrificial element allowance and need for aggressive cutting is desired such as in the case of removing tenaciously adhered Portland cement staining from a poor repointing job or from a cementicious whitewash when the substrate is common fieldstone that has no intricate carving. Modern brick will lack the porous "salmon" center known to be the remaining condition of an historic brick fired in a down-draft kiln. Modern bricks are thoroughly fired in a tunnel kiln which results in more uniform densification throughout. But even modern brick will become "pitted" by the sharp sand action of a sandblaster. If any case where all the drawbacks and limitations are realized and anticipated beforehand still warrant the use of sand as the medium, this method is at your disposal if a test sample proves it is effective. However, be sure of this fact. The surface area of masonry which is exposed to the elements is increased once sandblasted and micro-cracks may be introduced by any violently aggressive sandblasting especially by inexperienced operators. A final draw back in the use of this already unpopular method is that silica dust will be produced. At least a water mist used as a knockdown to dust must be engineered into the application. Water greatly reduces the dust when the sand comes out of the orifice and is pulverized into dust upon impact. A vacuum sandblaster is used when one must collect all of the contaminant such as paint along with the sand. Some municipalities do not allow sandblasting of any kind because of the negligence and misuse of the tool and because of the irreversible damage caused to historic structures. Not allowing sandblasting is generally a good idea since more damage is done than good over all. Should you let him sandblast? Most probably not.
Traditionally the only exposed stone is one with a gauged mortar joint. "Free stonework" are irregular pieces of stone shaped to fit with large, squared corner stones with alternating lengths used as borders. Ashlar work is varying sizes of cut blocks of stone that are laid in uniform coursing. You will sometimes see semi-coursed stonework on the front of a building and haphazard stone joinery on the sides and the back of the building. If the stone was shaped with tools used by masons it most likely was meant to be seen. You will often see remnants of the original external plaster or whitewash in the pours of the stone of the building which has already had the stucco removed to tip you off that the building was originally covered or coated and not exposed.
Fieldstones are stones picked up off the field when settling a property and preparing the ground for farming. They are laid up in "rubble work." Some masons pronounce it "roobil" work. I think they are just repeating the accent of the old-timers. Rubble is junk. Fieldstone is just junk stone It is not dressed up in any way.
But the question remains, "Why did they cover the stone with exterior plaster?" Well, when you don’t gauge the joints and keep them tight the surface exposure to the elements is increased and accelerated the erosion of the pointing mortar. This may quickly deteriorated the bedding mortar and the integrity of the wall. It will at least aid in the transmission of water into the building. So, the same soft, punky mortar that was used for bedding was also used for exterior plaster, (stucco), and finished off with a shelter coat of whitewash. Whitewash is pure calcium carbonate lime and water. It was used as a waterproofer and protecting coat for both beauty and function. Whitewash could be thought of as a coating like an eggshell. It is soft, breathable and will protect the otherwise frail stucco render. Today the appearance of rubblework exposed is thought of as a thing of beauty. Historically fine stonework was squared and formal with straight, true and gauged joinery as the sign of high-end work. Really, it still is throughout the world, but "beauty is in the eye of the beholder." If historic stone buildings where not plastered, (receiving an external stucco render), but instead received the inverted “v” joint to deflect the downward and angled drive of the rain, they usually were whitewashed right over top of the stone and joint in rubble work. When you don’t see the whitewash over the stone anymore it is because the acidity of a constant rainwater bath has loosened it and it has come off and was not renewed. More often than not it remains under the porch of houses and forebay areas of barns where it has been protected. Look closely in the pours of the stonework on the sides of the building and under the eaves or behind pent roof to see it remnants of the stucco or whitewash has remained. Another tell-tale sign that the building was originally stuccoed over the stone is that the widow trim remains proud to the stonework. If the trim comes out past the stonework at a thickness of 1-1'1/2" past the stone, then that is indicative that the stone was covered with stucco the meet the outer edge of the wood trim.
The only insulation gained by exterior plaster is that of slowing a driving wind. Overall masonry is a poor insulator. 1940 and newer stucco may have had perlite incorporated into the mix to add an insulatve element.
To correctly restore something would mean to put it back to its original design. For correct architectural restoration of a stucco over stone building means that the plaster should remain and be finished as it was originally. However, many people with unsound exterior plaster, which has lost its bond to the substrate or has cracks throughout it or has paint that is flaking, consider the removal of the offending stucco and coatings without replacing it but rather exposing, cleaning and repointing the stone. It is an option that will help mitigate the water infiltration problem. It is an option for overcoming the eyesore of flaking paint. It even increases the value of the building in many cases more than what the cost was to expose and repoint the stone. But my advise is to “just say no” when you have a formal exterior such as a building with a mansard roof. An exposed stone building which has been repointed and does not have the stucco or whitewash renewed should be reserved for a simple country farmhouse, outbuilding or barn in my opinion. It may effect the value of the property in a negative way by removing historic details. A local historic appropriateness review board may not allow these modifications and a historical society may frown upon changing the unique and appropriate details originally found at the historic structure.
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Surface pointing, (also known as a "scrub joint" ) is commonly applied as a pasted joint with little depth of material. It is in fact the most common method of "repointing" a whole building but contributes very little. In fact many times this method accelerates deterioration by trapping water in the wall with high concentrations of Portland cement in the mix used. Many masons utilize this method because pasting over the top of slightly recessed joints with a thin overlay goes up very quickly and gives the appearance of a lot of work received for what is a small amount of money charged for the work. In the end, the less than savvy building owner may think that since the entire wall has been "repointed" and now has a uniform look with all of the joints filled that they have received a good value. |
The fineness of Portland cement and fine play sand made in a 1:1 ratio with little or no lime content is often what is used to make this fine paste. The brittle, often gray Portland cement colored, scrub joint cracks and falls out within a few years.
Where the scrub joint does not fall out and was filled into deeper voids it only helps to keep moisture trapped in the bedding mortar. This allows any moisture in the wall to escape through the face of the masonry unit if it were to get out at all. A resulting "picture frame" of proud gray mortar remains with hollowed back masonry units as the final irreversible damage. "Tuck pointing" is what some inappropriately call the scrub joint. The scrub joint is very similar to grouting the face of tile although the scrub joint is applied course by course on the brick joints. The actual root of the name "Tuck pointing" comes from a narrow keyway cut into the center of a molded brick joint and then filled or "tucked" with a bright white, red or black lime putty to give a more formal and gauged appearance to the brickwork.
Prior to the tucking in of this lime putty a red color wash used to be applied first to the bricks and to the background mortar joints to give uniformity and aid as a shelter coat. Remnants of this color wash and infill of putty can be found on many historic brick buildings in the eastern states. The "grapevine joint" has taken the place for the name of a true ruled-key tuck pointed joint in my opinion. The grapevine joint is often reproduced in a restoration effort without the proper color wash and lime putty in-fill. This is a side note but shows that hastily going into repointing can result anywhere from improper working dynamics to a wholesale misinterpretation of the original design detail which alters the historic accuracy of the building in its setting.
Do you travel to consult or perform work ?
Yes. Here are some local and some not so local examples of our consulting work:
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Denbigh
Hall Condominiums, Wilmington Delaware |
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Denbigh
Hall Condominiums, Wilmington Delaware |
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Andy
deGruchy taking moisture meter readings. We were hired to hunt down leaks in the large building and put together a plan to correct the root cause. A year later we fulfilled the plan and spent over a year executing the work to solve the water infiltration problem to the building. |
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| A small luxury hotel located in Massachusetts where we prepared an intervention plan and put preliminary budget numbers together to carry out the plan. |
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| This is the deLabra School in San Turce, Puerto Rico. The General contractor who won the project had me visit the site and spend a few days reviewing specifications and preparing a masonry restoration bid. |
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