Damaged Bricks, The Quick Moving Culprit? FAQ by Randy Ruth

by Randy Ruth

Bricks can hollow back quite profusely in some cases. What are some of the causes?

Don’t forget vermin. Accelerated wetting and drying cycles near the bottom of the brick building cause an increase in the decay of the soft bricks. However, where there is water and calcium rich lime mortar there can be ants and bugs nesting in and behind the wythe. Masonry Bees are found in some parts of the country and will burrow. Sparrows and Starlings will take the calcium bits from lime mortar and like a cuttle bone use the grains for digestion. Some very deep holes in the brickwork are from wood peckers who sense the presence of the bugs and they hone in on certain areas in an attempt to get to them. Here’s one example that may have been caused by a combination of water and animals.


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Lime Paint and Plastering System for Interior Application, FAQ Friday

Building on last week’s FAQ Friday, the use of lime paints doesn’t have to stop with use on the exterior of a building. Lime paints are great for use on interior walls by themselves or used as a pre-hydrated and dispersed pigmenting agent that can be mixed with Ecologic Mortar, NHL, or a combination of the two when formulating your own colored plasters.

There are many benefits of using lime paint on internal walls but there sometimes needs to be some preparation involved to make sure that the lime paint or plaster will adhere to the substrate. Often times I hear that someone will want a colored plaster finish on their interior walls but they do not know if lime paint will adhere. The simplest way to check is to spritz some water on the wall. If there is no absorption of the water, the wall is either too smooth or not porous enough. We need some suction. One way to achieve this is to apply a base coat of Takcoat™.

Takcoat™. was discussed in detail in a previous FAQ Friday So to keep it short I will just say that it is a VOC free, transitional lime and sand prepared plaster material that can be applied to smooth painted or unpainted surfaces. Once Takcoat™. is cured then adequate suction and mechanical key is provided for Lime Paint and lime plaster to adhere to the wall surface. There are ranges of different lime finishes that can be applied to the wall ranging from a rough open pore surface texture to an incredibly smooth polished Venetian or Tadelakt finishing style. The finish is dependent on the client’s wishes and the skill level of the craftsperson.

In my opinion, craft skill level is fundamentally dependent on the tools a craftsperson has at their disposal. One important tool to have when formulating different plasters is pigmentation. The lime paints we sell at LimeWorks.us come in a variety of colors that can be used as integral pigments mixed into plaster formulations or on their own as a decorating top coat. Having a good pigmentation methodology gives a craftsperson more options during the planning stages of a project. A good pigmentation methodology also makes reproduction of the mockups on to the entire application easier once a decision has been made on a certain color since the consistency of our products makes this a smooth process.

Lime paint comes as a dry powder consisting of a high calcium lime paint base and dispersed pigments if the paint is a colored one. Dilution of the lime paint with water to make a quart, gallon or 5-gallon unit will further breakdown the pigment and further slake the hi-cal lime. When a known volume of paint has been made it can be used in Ecologic Mortar formulations or gauged into lime plaster for color.

So whether you know what style of plaster finish you want to achieve or you would rather let your imagination run wild and experiment, just contact us and we will be able to help you develop your plaster system to ensure a successful project.

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All About Lime Paint, FAQ Friday

Although they date back thousands of years, some of the best examples today of lime paint are those pictured in scenic postcards of gleaming white and pastel colored villages, so abundant throughout the Mediterranean. Many architects and designers currently seek a return to these methods and products of the past. Lime paint changes and evolves as it slowly ages, giving buildings an appealing, provincial look. Additional coats can be added as time goes on, enhancing the depth of colors. Modern paints often seal in humidity, which later leads to peeling and other exterior damage to a building’s surface. More like a stain than paint, lime paint is absorbed into the wall, penetrating the background. Once cured, the lime paint allows the surface to breathe, becoming a peel-free surface as it allows humidity to escape.

Lime Paint base (Natural), has no color added. It can be used to whitewash an old masonry building with only two coats and turn a dingy structure into a “museum-like” historic landmark. This is the Gambrel Roof House in Historic Fallsington, PA.

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A home in Lambertville, NJ originally had a shelter coat of lime wash put on the soft under-fired brick. #345 St. Astier Lime Paint was used to refresh the building, protect the brick and maintain good breathability for the coating so as not to trap moisture in the wall.

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A home in Stirling, Scotland which has had the facade restored using colored limewash over a lime/sand render. The home is located along the way up to Stirling Castle.


The Coastal Heritage Society Preservation Team members of Savannah Georgia whitewashed the retaining wall at the Roundhouse Railroad Museum using St. Astier lime paint.

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A home in Massachusetts originally had a harled finish coat of lime stucco. The St. Astier Lime Paint #429 was used to refresh the building’s exterior look while protecting the soft lime stucco with a “like to like” compatible coating that will wear down over time rather than flake and peel off. The work was accomplished by Florentine Masonry Restoration.

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Lime Mortar and Hardscaping, FAQ Friday with Randy Ruth

When it comes to hardscaping with masonry, I am all for mortarless construction. The beauty of a well built dry stacked stonewall or paver application creates a natural aesthetic on any property. Often times however, there is a need or desire for a more permanent structure requiring mortar. Traditional brick garden walls in a Flemish bond pattern are a particular favorite of mine. The truth is hardscaping options are endless with so many creative ideas for an architect or master mason. Variations in brick bond patterns can come up abruptly with changes in architectural style creating such visually stimulating surround that once immersed, one may find themselves in a peaceful wholesome setting. I find myself not feeling this way in locations recently constructed but in older, aged locations, where there is a bit more character. This character comes from the details in construction.

With mortar taking up about 20% of the surface area on a wall, it is no surprise that mortar detail has a subtle yet powerful effect on the visual appearance of a masonry wall. In the construction of modern brick walls, Portland cement sticks tenaciously between the bricks, with characterless mortar joints. The two most prevalent types of mortar joints I see are concave and grapevine. While the concave mortar joint is meant to keep a watertight seal between the brick, it looks out of place. Rather it would be happier on the façade of a modern home, office building or utilitarian structure. The grapevine mortar joint style might be a romanticized take on old historic brick jointing that is often abused in modern construction but is not as aesthetically displeasing.

Despite my opinions on joint profiles, it’s the overall appearance that a modern Portland cement causes a hardscape wall to have. Unsightly control joints and modern joint profiles are a direct result of mortar used on a hardscaping project. The use of lime-based mortar can counteract such unsightly details and can be truer to the envious historic gardens of yesteryear in aesthetic quality.

Construction of hardscaped brick walls do not need to have control joints when lime is employed as the primary binder in lieu of Portland cement due to lime’s natural flexibility and free lime content which permits autogenous healing of micro-cracks. The use of lime in new construction is also “green”. The carbon footprint of using lime as a primary binder reduces co2 emissions by as much as 80% when compared to Portland cement. This reduction in emissions represents a greater step forward toward sustainability in our built environment. The breathability of lime mortar also promotes the idea of free flowing and natural earthen feelings associated with hardscaped locations. When our spaces work with moisture and process water rather than trying to trap it, a harmony is produced. This can help bring into sync the man built environment with the natural growing environment of an outdoor space.

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Reconstruction of Historic Lime Mortar and Renders FAQ Friday


Q: I want to restore my old stone house and have heard there are ways to reuse the mortar already in my building during the repointing process. Can you explain how to do that and what are the positive and negative impacts?

A: Reusing old historic mortar is possible in more ways than one. The first methodology would be to leave sound mortar alone and keep using it for as long as possible, only doing “patch” pointing in areas that need to be fixed. In cases where a building owner desires to repoint the whole building you can follow the backyard guidelines below.

Of course if one were to follow these guidelines then there must be a conservation mindset in the back of their head. Knowing this, a mortar analysis would be highly recommended to help conclude an appropriate mortar mix design.

Reconstitution of historic lime mortar and renders

The purpose of this procedure is to separate the lime from the historic aggregates to reproduce a mortar joint or render while retaining as much of a buildings historic fabric as possible without the use of acids.

Beginning with the removal of any loose, cracked or friable render or mortar in the gentlest means possible, put debris aside.

Using a concrete barrel mixer place all saved debris in the mixer with large heavy stones or steel balls, about the size of a bowling ball. Make sure that the chosen crushing medium is harder than the debris to minimize contamination of the crushed aggregate by foreign matter. The mixer should be filled only to the point where the crushing medium will effectively fall from the apex of the mixing rotation and crush the debris to what would be the consistency of a pre-blended dry bagged mortar. This process should take anywhere from 20 – 60 minutes depending the quantity of the material loaded in the mixer (less is faster) and the desired fineness of the aggregates. Be sure not to over mix. Over mixing will result in the deformation of the aggregate.

Once the debris has been crushed to the desired particle size, place in 5-gallon pails or wheelbarrow for the separation process.

Place the end of a hose running water beneath the crushed aggregate. While the container is filling with water be sure to slowly agitate the wet aggregate mix with a hoe or trowel. Be sure to allow the fine lime particles to spill over the sides of container to be discarded. Make sure that the larger aggregate stays settled to bottom of the container for reclamation. This process should take approximately 20-60 minutes depending on amount of crushed debris and its binder to aggregate ratio. The process is completed when the water runs fairly clear and the remaining fines in the mixture can be easily made into a ball that resembles saturated beach sand.

Upon completion of filtering the lime from the aggregate allow to dry in the open air and strong sun by spreading it out on as thinly as possible over a tarp.

Once the aggregates are dry, the large particles of broken stone, any other foreign matter and large unbroken debris can be dry screened out using the desired sieve size. Typically anything retained on a #4 sieve can be discarded.

Now that the aggregate is dried and sieved, new mortar formulations can commence. Depending on the amount of work to be done with the reclaimed aggregate and the amount that was actually reclaimed, determination of how much other similar aggregate is to be gauged in to the new repointing or rendering mix.

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Stucco Over Historic Stone Buildings, FAQ Friday


Q: Why are beautiful stone farmhouses and other historic stone buildings covered with stucco? Is it for insulation? If the stucco over stone is an original and historically accurate detail, is it then OK to remove it to expose the stone and leave it that way? Will this enhance or deflate the value of the building in its authenticity?

A: 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 deteriorate 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 if remnants of the stucco or whitewash have 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 to 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 insulation 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.

Sandblasting Historic Buildings FAQ Friday


Q: Someone wants to sandblast my house. Should I let him sandblast?

A: 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-invasive 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.

Using Natural Hydraulic Lime in cold weather, FAQ Friday with Randy Ruth


As fall encroaches upon us with its cold weather, a question that is going to be popping up with more frequency is… Is it too cold to start or finish my project with NHL?

This may be one of the most difficult questions to answer, where the wrong answer can result in a lot of lost time and damage. The simple and safest answer is, do not perform work with NHL when temperatures will fall below 40 degrees Fahrenheit (including wind chill) for at minimum 7 days after placement of the mortar. Even following this model answer can result in frost damage of the mortar in some cases. So what is an applicator to do, to ensure that their work will last a reasonable amount of time? Well, care, caution, attention to detail, and patience is the answer.

If you can wait until spring to complete the project then you probably should to play it safe. If however, you absolutely need to complete the project before winter and do not mind playing with fire, then tenting and heating the scaffolding is an option. Tenting and heating can cost a lot of extra money in labor and fuel, so obviously make sure that there is enough money budgeted aside to warrant this approach.

By completely encasing the scaffolding envelope with heavy-duty plastic and being sure to affix the uppermost part of the plastic to either the roof or its eve, one can create a tight enclosed space for heating. When using a heater make sure that it is in a safe place and slightly raised off the ground. You should refer to any local building codes to make sure that you are in compliance and most importantly safe.

Of course, good masonry practices should not be skipped over just because the work is tented in and heated. Damp curing with burlap is still recommended and when repointing work is being executed good compaction of the mortar against the background mortar is still a must.

There are a few other tricks available to the applicator that can help prevent frost damage. One is the use of air-entrainment in the mortar. Careful dosing of an air-entrainer can help but not eliminate frost damage due to improper curing practices. Adding air-entrainment must be done with caution, as too much air in a mix will make the mortar weak and friable. When using proprietary admixtures, proper testing should be conducted to make sure that there are no adverse side effects .

Lowering the water content of the mix and increasing mixing time will help reduce the amount of water available to freeze without sacrificing too much workability. The use of warm mixing water, preheated sand as well as preheating the masonry units will help slow the development of frost. Winter accelerators associated with working with Portland cement mixes should not be used, such as calcium chloride or any nitrates. Depending on the properties of the surrounding masonry units NHL 5 can be appropriate to use in a masonry mortar to help withstand frost, due to its faster setting time.

When in doubt about working in possibly freezing conditions or allowing recently completed work to be exposed to freezing temperatures, you should probably trust your gut and call it a season. Dancing with the weather can be costly and should be avoided.

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Wet Basements and Masonry… FAQ Friday with Randy Ruth

Basements are notorious for moisture problems. Mold can spread quickly and cause serious health problems throughout a home. Here is another frequently asked question from Randy Ruth about basement moisture and masonry.

Q: I am having moisture issues in my old stone farmhouse, especially in the basement and I’ve noticed a few places where mold appears to be growing. I was told it could be because of the masonry but I don’t understand how that’s possible?

A: It should be noted that most old stone farm buildings were primarily build with lime mortar, especially before 1900. The source of for the lime used during its construction would have been local and probably made in a kiln on the side of a hill, by an experienced lime burner. What all this means is that the mortar between the stones would most likely be soft, with an affinity for water and have relatively good vapor exchange. Those characteristics are quite the opposite when compared to today’s Portland Cement based mortars.

Moisture from old stone walls can occur on the inside a building and can predominantly be evident in the basement. Accompanying the moisture can be mold, which can result in a decrease in indoor air quality and overall health. Such a problem should be addressed accurately and swiftly to minimize health risks. In order to identify an approach to this problem more information needs to be gathered and thought about.

Was there any recent work done to the exterior of the building?

Sometime when a non-breathing sealer or cement render is applied to the exterior of an old breathing building, natural moisture inside the wall can become trapped. When moisture becomes trapped inside of a wall it will travel to the point of least resistance. Often times this is the interior of a wall resulting in excess moisture accumulating on the wall. The excess moisture, typically above 20% can create a breeding ground for bacteria so long as there is a food source.

If paper faced drywall was installed on the interior of the building accompanied by such exterior work, then the moisture can not only deteriorate the gypsum in the drywall but also give the bacteria a food source. The bacteria resulting mold on the surface can consume the paper face of the drywall.

Has the landscaping around the exterior of the building been changed?

Down spouting and improper detail to appropriate grading can also be a culprit in moisture ingress. If water is pooling in areas and not being carried away from the building appropriately, excess water can penetrate the stone wall to the point where it is noticeable and cause mold problems.

The point here is that something has probably changed in or around the building in recent years to allow excess water in the building. There are many different remedies for water ingress for historic buildings, all of which have some merit and may be appropriate depending on the specific issue. However, complete and proper excitation of a good remedy is always crucial to success for any project.

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Burning Lime, The Traditional Way

This is an incredible video that really shows the difficulties of burning limestone the old way. Stacking wood, limestone and coal in an old kiln these men go through the process using traditional methods to turn regular limestone into caustic burnt lime.

Uploaded on Nov 27, 2010

This is from the Edwardian Farm series – how to make 10 tons of lime mortar in a massive kiln using layers of limestone and coal burnt for days!


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