Historic Fabric melded with Traditional Mortar at the Irish Hunger Memorial in New York City

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Blocks from the World Trade Center Memorial and the construction site of the new World Trade Center sits a half acre patch grass dedicated to raising awareness of the Great Irish Famine. This memorial was under construction on September 11, 2001 when the Twin Towers fell. The memorial saved that day, simply because of the direction the wind was blowing. The plume of dust blew from 1 World Trade Center in just a way that it didn’t touch a single stone, all of which were donated from each county throughout Ireland. Even a 19th century cottage was disassembled in the County of Mayo and re-laid in Manhattan using a lime mortar that was determined to most closely match that of the original. The memorial was dedicated in 2002 by former New York mayor Ed Koch.

A team from LimeWorks.us recently visited the site and put together a collection of images seen below. The names carved in the stones represent the counties of Ireland. St. Astier Natural Hydraulic Lime was used throughout the memorial walls and cottage, supplied by LimeWorks.us. The structure has been holding up very well and we are very proud to have been part of this important piece of built heritage.

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All photos Copyright Sean K Maxwell

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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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Green Construction in Today’s Built Environment – FAQ by Randy Ruth

by Randy Ruth

When people talk about “green” construction, I often wonder what the environmental benefit of the construction is. Is it new construction? If so what is the environmental impact? I would hope that a perfectly good existing building wasn’t torn down to make way for supposed progress.

It is my belief that the greenest building is the one that is already standing and most likely played a role in a community’s development. It could be an old department store, manufacturing warehouse or barn. Sometimes plans call for only the façade of a building to be saved which helps keep the architectural integrity of a community intact. This can be a positive compromise because the more useful modernized building can be built and yet some historic fabric is retained to tell the story and retain the flavor of what the building was in its local context.

In the end, as long as something is retained for adaptive reuse, whether it is for aesthetics or the entire structure, there is a measure of success in reducing a “green” construction project’s carbon footprint.

In most instances, a building that has been saved from the wrecking ball is old. What does old really mean? Well that’s pretty subjective but I would like to think of old in the context of US building history as being pre 1930, or roughly 80 years and older. When an old building is going to be adaptively reused one way or another then appropriate materials should be used to fix what is broken with compatible repair materials. Using in-kind repairs will further promote the legacy and overall usefulness of a building for years to come while lowering its impact on the environment.

Old buildings are usually very strong and often made of brick and stone that has proven to stand the test of time. However it’s the mortar that binds those materials together and meant to be sacrificial. Mortar should fail first not irreplaceable historic masonry units. The embodied energy to replace a masonry unit is much greater than the mortar. Therefore, it is imperative that a suitable replacement mortar be used to mend what is failing and the mortar be weaker and slightly more permeable than the surrounding masonry units.

In the case of masonry mortar, lime is typically the binder in these old buildings and should be regarded as key to the dynamic that has allowed the building to be in service so long. Often the original mortar is still in place, proving its superiority and therefore should be replaced in-kind. The use of modern day Portland cement based mortars, which are stronger and denser when placed over the top of lime based mortars, are less sympathetic to the historic masonry and can trap moisture causing further damage to the historic fabric. The historic masonry units and adjacent historic elements can best be kept in conservation with the use of the right lime mortar. The correct Natural Hydraulic Lime (NHL) mortars when used where they are appropriate can become a compatible repair materials that is sympathetic  to the working dynamics of an historic masonry building. Secondly, NHL mortars remain reversible without damage to the building unlike the alternative which is the too over-used hard, brittle and dense Portland cement based mortars which are known to cause irreversible damage in conjunction with historic masonry fabric.

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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.

Examples:
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.

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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

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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

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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.

How Lime Mortar Traditionally Got it’s Color and How We Can Replicate this Today – FAQ by Randy Ruth

by Randy Ruth

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Seven factors that can affect the color of lime mortar in no particular order of significance, Lime, aggregate, pigment, water content, rate of absorption, original surface texture and erosion. By its self, the color spectrum of lime can vary from bright white, light grey, slight pink or ochre colors. This color is dependent on a few factors such as the original stones chemical makeup and burning temperature. When an appropriate limestone is thoroughly burned (calcined) at a particular temperature to produce hydraulic or non-hydraulic quicklime and then hydrated to produce either a lime putty or dry lime hydrate, the result will be a white or off-white color. The first factor affecting the whiteness index of the lime will vary depending on the raw mineral impurities in the limestone. A limestone with a higher calcium content with all other factors aside will produce a whiter hydrated lime. If that same limestone is burned at a slightly higher temperature, the result will be a slightly grayer hydrated lime. Although, lime plays a role in the final color of a mortar, its significance today, when replicating a mortar joint is minimal, often due to the lack of availability or technical characteristics like Hydraulicity. Aggregate has a huge effect on the color of lime mortar. Historically aggregate for masonry mortar would be sourced from either local sand beds, found near creeks or rivers, or from the trimmings of stone on site and possibly brick pieces or dust as a pozzolanic additive.

The larger screenings of the aggregate play a role in the overall tone of the final mortar color but it is the fines that do most of the work. The smallest particles in the aggregate AKA fines will give the biggest impact on the final color. Brick dust, limekiln dust and clay impurities are pozzolanic fines that can be found accidentally and at times intentionally accompanying the aggregate. Today these impurities are almost never allowed into a replicate mortar mix, as the resulting technical data from such a mix design is often cost/time prohibitive for a project even if historically appropriate. As a result powdered pigments are often used today to achieve a particular mortar color. Just because pigments are predominantly used today in mortar mix designs, doesn’t mean that they weren’t used over 100 years ago. Colored mortar is an important design element in any building of today and yesteryear.

The types of pigments used in mortars have not changed all that much in past few hundred years. Iron oxide, carbon black, and natural ochre’s hold a solid footing in the industry today, each presenting their own limitations. It has been proven that carbon blacks can fade dramatically over a 30 year period in masonry mortar. Even though their tinting strength is very good, if not controlled carefully shades of grey can be very difficult to achieve. Natural ochre’s can produce wonderful colors and be very accurate when making accurate replicate mortars. The problem is in their tinting strength, and consistency in production on a large-scale. It may take above a 10% dosage of natural pigment to achieve the same color in a mortar using iron oxide pigments conforming to ASTM C979. Because of their durability, tinting strength and quality in production, iron oxides have been deemed the best pigment for coloring mortar on a large-scale. Even when using appropriate pigments at the correct concentration, water content in a mortar plays a big role in determining final color. Using the same exact mix in two batches and varying the water content by 10% will produce a significant change in color. From experience, I have noted that this problem is most evident when trying to achieve a red colored mortar. Light grey’s can also be problematic but are less evident and are usually deemed acceptable. That is why it important to measure all ingredients in a mix carefully to ensure consistency from batch to batch. The practice of mixing mortars consistently should carry over to pre-dampening of masonry units. By pre-dampening consistently as possible, the rate of absorption is controlled. This is a good practice just so mortar will not reach a flash set, and to control curing of the mortar which plays a role in the final color.

 

There is some debate on how a replicated mortar should look when not replacing all the mortar. Should it look new, with a smooth surface that stands out because of the way light reflects off two different surface textures? Alternatively, should it blend in with adjacent mortar joints? Personality, I believe in the latter. If a new mortar is inherently the same color at its core as the old historic mortar, than even though a slicked smooth replacement mortar will eventually blend in it can still distract the eye. A good repair for just about anything should be as seamless as possible. Besides, won’t a different texture erode differently, resulting in the continuation of a miss match over time? This brings me to erosion in mortar. As a mortar erodes, the color of the aggregate begins to come through. This color can sometimes throw off the human eyes perception of what is the color to be achieved when color matching. Someone explained this to me so well once that I must share. He had asked a room full of people what the color of foam on the head of a beer is. All replied white in color. We all got it wrong. The answer is amber like the color of the beer. This is because of the way light is reflected back to the human eye off a larger Surface area. Now that is in extreme case of a dark color turning lighter but the principle is still applicable to mortar. However, in most cases the rougher the color the darker a mortar is, and depending on who well the color of the sand is matched, you may just get a replacement mortar that will be seamless for generations.

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Sandblasting Historic Buildings FAQ Friday

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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.