More On Architectural Masonry Restoration

Poulticing for Removing Graffiti and Stains

Stains and graffiti, that have penetrated inside of the masonry, are often most effectively removed through a poultice being used. A poultice is comprised of clay powder (such as fulleris earth or kaolin, or even shredded paper towels or paper) or an absorbent material, mixed together with a liquid (remover or solvent) in order to form a paste that is then applied to a stain. The poultice needs to be kept moist and then left on the stain for as long as needed in order to draw the stain out from the masonry. As the paste dries, it will absorb the staining materials so it isn’t redeposited onto the masonry surface again.

wall graffiti removal

Some paint removers and commercial cleaning products are specially formulated as either a gel or paste that clings to a vertical surface and stays moist for longer to prolong the chemical’s action on the stain. There are also pre-mixed poultices that are available as a powder or past that only need the appropriate liquid to be added. The masonry needs to be pre-wet before an alkaline cleaning agent is applied, but not when a solvent is used. After the stain is removed, the masonry needs to be thoroughly rinsed.

Mechanical and Abrasive Cleaning

In general, it is not appropriate to use abrasive cleaning methods on historic masonry buildings. The reason is that they are abrasive. Sanding discs, grinders, and grit blaster all operate through abrading the paint or dirt off of the masonry surface, instead of reacting with the masonry and dirt. That is how chemical and water methods work. Abrasives do not differentiate between the masonry and dirt, so they also can remove the masonry’s outer surface, and result in the masonry being permanently damaged. Polished surfaces, detailed carvings, soft stone, architectural terra-cotta, and brick are all especially susceptible to aesthetic and physical damage that abrasive methods can cause. Architectural terra-cotta and brick are fired products that have a glazed, smooth surface that can be removed by grinding or abrasive blasting. Masonry that is cleaned abrasively is damaged both physically and aesthetically, and it will have a rough surface that has a tendency to hold dirt. The roughness will also make it more difficult to clean the masonry in the future. Abrasive cleaning processes also can increase the chance of subsurface cracking on the masonry. Abrasion of the masonry’s carved details will cause the sharp corners to be rounded and other delicate features can be lost. Abrasion of a polished surface will remove the stone’s polished finish.

Mortar joints, particularly those that contain lime mortar, may also be eroded by mechanical or abrasive cleaning. In certain cases, the damage might be visual, like increased joint shadows or losing joint detail. Since mortar joints make up a high percentage of the masonry surface (in a brick wall up to 20 percent), it can result in losing a large percentage of historic fabric. When mortar joints erode, it might also allow increased water penetration, and that will likely result in repointing being necessary.

Read also: Cleaning Methods For Historical Architecture

Abrasive Blasting

Blasting using abrasive grit or some other abrasive material is the abrasive method that is most frequently used. Sandblasting is associated most commonly with abrasive cleaning. Some of the materials that are used for abrasive cleaning include finely ground silica, glass beads, glass powder, ground garnet, powdered walnut as well as other types of ground nut shells, aluminum oxide, grain hulls, plastic particles or even tiny sponge pieces. Although abrasive blasting isn’t an appropriate cleaning method to use on historical masonry, it may be used safely for cleaning certain materials. Quite often finely-powdered walnut shells are used to clean monumental bronze sculptures. Carved, finely detailed stone features and delicate museum objects with micro-abrasive units are also cleaned by skilled conservators using aluminum oxide.

Typhoon Sand Blaster …

There are a number of current abrasive blasting approaches that use materials that are not normally considered to be abrasive and are not associated commonly with traditional methods of abrasive grit cleaning. There are certain abrasive cleaning processes – one wet, one dry – that use finely-ground glass powder to remove or “erase” surface soiling and dirt only, but not stains or paint. Another patented process is cleaning using baking soda. Some communities use baking soda blasting to quickly remove graffiti. However, it shouldn’t be used to clean historic masonry since it can abrade it easily and may permanently etch graffiti in the stone. Also, it may leave behind salts in the stone that are potentially damaging that cannot be removed. A majority of abrasive grits can be used either wet or dry, although dry grit has a tendency to be used more often.

Pelletized dry ice or icy particles (CO2 or carbon dioxide), is another medium that is used for abrasive cleaning. It is too abrasive to use on a majority of historic masonry. However, it can have some practical application to remove asphaltic coatings or mastics from certain substrates.

Some of the processes are promoted as not causing damage to historic masonry buildings and environmentally safe. However, it needs to be kept in mind that they are abrasives and “clean” through removing part of the masonry surface, despite being just a tiny portion. The very fact that these are abrasive treatments needs to always be considered whenever a project for cleaning masonry is being planned. As a general rule, historic masonry buildings should not be cleaned using abrasive methods. In certain limited circumstances, gentle, highly-controlled abrasive cleaning might be appropriate on hard-to-clean, certain areas on a historic masonry building if conducted under the careful supervision of an experienced, professional conservator. However, an entire masonry building should never be cleaned using abrasive cleaning.

See also: Assessing Cleaning Treatments For Historic Buildings

Sanding Disks and Grinders

Grinding a masonry surface suing sanding disks and mechanical grinders is another abrasive cleaning method that should not be used on a historic masonry building. Disks and grinders, like abrasive blasting, doesn’t really clean masonry. Instead, it abrasively removes and grinds away, and therefore, damages the actual masonry surface instead of just removing soiling material.

Cleaning Methods For Historical Architecture

Cleaning Methods For Historical Architecture

Materials and Cleaning Methods

There are three main groups that masonry cleaning methods are usually divided into: abrasive, chemical, and water.

Water methods work to soften the soiling materials and dirt and then rinse the deposits away from a masonry surface. When chemical cleaning agents are used they react with paint, soiling material or dirt to remove them, and then water is used to rinse the masonry surface off. Abrasive methods include using sanding discs and grinders, and blasting with grit, which all mechanically remove paint, soiling material, or dirt (and some of the masonry surfaces as well, usually). Often a water rinse is used following an abrasive cleaning. Laser cleaning, although we will not be discussing in detail here, is another technique that conservators sometimes use for cleaning small historic masonry areas. However, it is expensive, so for a majority of historic masonry cleaning projects, it is usually not practical.

See also: Assessing Cleaning Treatments For Historic Buildings

texture-water-washAlthough it might seem to go against common sense, you should carry out masonry cleaning projects by starting at the bottom and then working your way up to the top of the building, while keeping all of the surfaces wet that are underneath the area that is being cleaned. The reason for using this type of approach is based on the fact that cleaning effluent or dirty water dripping from cleaning above will leave streaks on dirty surfaces but won’t streak a clean surface if it is kept wet and then rinsed often.

Water Cleaning

In general, the gentlest possible methods are water cleaning methods. They can safely be used to remove dirt from all kinds of historic masonry. Essentially there are four types of water-based methods: hot-pressurized water or steam cleaning; water washing with a non-ionic detergent supplement; pressure water washing; and soaking. After water cleaning is complete, it is frequently necessary to follow up by rinsing with water to wash the loosened soiling material off of the masonry.

*It might not be appropriate to use water cleaning methods on some masonry that is badly deteriorated since the water might exacerbate the deterioration, or on alabaster or gypsum, which in water are very soluble.

Chemical Cleaning

In general, chemical cleaners that are in proprietary product form, are another type of material that is used frequently for cleaning historic masonry. They can remove paint, other coatings, dirt, graffiti, as well as plant and metallic stains. Chemical cleaners that are used for removing soiling and dirt include organic compounds, alkalies, and acids. Of course, acidic cleaners should not be used on any acid sensitive masonry. Paint removers are based on organic solvents or other types of chemicals and are alkaline.

Chemical Cleaners for Removing Dirt

Both acidic and alkaline cleaning treatments include using water. Both of these types of cleaner are likely to also contain surfactant (or wetting agents), for facilitating the chemical reaction for removing dirt. Usually, the masonry is wet down first for both kinds of cleaners, and the chemical cleaner is then brushed on the surface or spray at very low pressure. The cleaner is then left on the masonry for whatever amount of time that the product manufacturer recommends, or, preferably, is determined through testing, and then is rinse off using a moderate or low-pressure cold water wash, or sometimes hot water is used.

It might be necessary to apply more than one application of cleaner, and it is a good practice to always test the recommendation of the product manufacturer regarding dwell times and dilution rates. Since every cleaning situation is unique, dwell times and dilution rates can vary greatly. The masonry surface can be lightly scrubbed with synthetic or natural bristle brushes before being rinsed. After it is rinsed, there should be pH strips applied to the surface to completely neutralize the masonry.

Acid-based cleaning products can be used on non-acid sensitivity masonry, and in general will include: concrete, cast stone, architectural unglazed terracotta, unglazed brick, slate, most sandstone, and granite. A majority of commercial acidic cleaners are primarily composed of hydrofluoric acid and often contains some phosphoric acid in order to prevent the development of rust-like stains on the masonry after it is cleaned. Acid cleaners are then applied to pre-wet masonry. The masonry needs to be kept wet while the acid is at “work” and then use a water wash to remove it.

On acid-sensitive masonry, an alkaline should be used, including on polished granite, architectural glazed terracotta, glazed brick, calcareous sandstone, unpolished and polished marble, and limestone. (Sometimes alkaline cleaners can also be used on non-acid sensitive masonry materials – after they have been tested first- but might not be as effective as they are when used on acid-sensitive masonry). There are two products that alkaline products are primarily made of: an alkali, like ammonium hydroxide or potassium hydroxide; and a non-ionic surfactant or detergent. Alkaline products, like acidic cleaners, are normally applied to pre-wet masonry, and then allowed to dwell, and finally, water is used to rinse it off. (A longer dwell time might be needed with alkaline cleaners compared to acidic cleaners). There are two extra steps that are needed following the initial rinse to remove an alkaline cleaner. First, a slightly acidic wash is given to the masonry – often using acetic acid in order to neutralize it, and it is then rinsed with water again.

Chemical Cleaners for Removing Paint, Other Coatings, Graffiti and Stains

brick and motar wall deteriorationRemoving paint, as well as some other types of coatings, graffiti, and stains are best achieved with cleaning compounds such as organic solvent paint removers, or alkaline paint removers. To remove paint layers from masonry surfaces normally involves applying the chemical cleaner using either a sprayer, roller, or brush, and then followed up with a water wash. Like with any form of chemical cleaning, any manufacturer’s recommendations on application procedure should be tested first before starting on the work.

Usually, alkaline paint removers have the same composition that other types of alkaline cleaners do, and contain trisodium phosphate, ammonium hydroxide, or potassium. They are used for removing acrylic, latex, or oil paints, and effectively remove multiple paint layers. Alkaline cleaners might also remove certain water-repellent acrylic coatings. Like with other types of alkaline cleaners, a final water rinse and acidic neutralizing wash are usually needed after an alkaline paint remover has been used.

Organic solvent paint remover formulations vary and might include various combinations of solvents, which can include toluene, xylene, acetone, methanol, and methylene chloride.

Other Cleaners and Paint Removers

Other cleaning compounds that may be used for removing some painted graffiti and paint from historic masonry can include paint removers that are based on petroleum-based compounds or N-methyl-2-pyrrolidone (NMP). Removing stains, whether it is biological (fungal and plant) or metallic (copper or iron), or industrial (tar, grease, soot, and smoke) in origin, will depend on matching the kind of remover carefully to the specific type of stain. Removing stains successfully from historic masonry will frequently require applying a number of different types of removes before finding the right one. Removing paint layers off of a masonry surface usually will be achieved through applying the remover using a sprayer, roller, or brush followed up with a thorough water wash.

Assessing Cleaning Treatments For Historic Buildings

Assessing Cleaning Treatments For Historic Buildings

One of the major causes of damage to historical buildings is improper cleaning and coating services. One or the other may be appropriate in some specific situations, however, both treatments may cause serious damages and even destruction to a historical building if they’re not done properly. Historic masonry includes brick, stone, architectural Terra-cotta, concrete and concrete blocks, cast stone and more. Often, it’s cleaned in an effort to improve the appearance of the building, however, this is where damage may occur. If not done properly, it may actually cause more harm than good according to historical records.

It would be wise choice, when selecting a commercial cleaning company in Vaughan, do do any commercial cleaning including exterior cleaning. There are hundreds of companies in the area but only a few who know what their doing when it comes to historical restoration.

The goal of this article is to offer important information regarding the variety of proper cleaning methods and materials to ensure that the exterior of a historical building is properly cleaned and maintained. It’s vital to the integrity of the building to ensure that the proper and most appropriate method of cleaning is undertaken. It’s important to understand the difference between water-repellent and waterproof when considering the purpose of each. The suitability of the various applications for historic masonry as well as the potential consequences of using inappropriate methods are fully discussed and investigated in this article.

historical downtown Toronto buildings

With the intent of understanding how sensitive historic masonry can be and what makes it extra special, this article is intended for historic building and property managers who are working alongside architects and architectural conservators as well as contractors in an effort to restore such buildings to their original state. While specifically intended for historical buildings, it’s also very applicable to any masonry building. This article expands on the Preservation Briefs 1: Cleaning and Waterproof Coatings of Masonry Buildings. It’s not intended as a cleaning manual nor as a guide for preparation specifics. Instead, it’s intended as general information that is to raise awareness of the factors that are involved in choosing the proper cleaning methodology and the proper water-repellent treatments for all historical and non-historical masonry buildings.

Preparing For The Cleaning

Reasons For Cleaning

cleaned masonry stone wall example

First and foremost, it’s vital to determine whether or not the masonry is in need of cleaning. The main objective of cleaning any historical masonry is to consider why it needs to be cleaned. There are many serious reasons to clean a historical building. 1. To improve the appearance of the building by removal of any dirt or soil or debris. 2. To remove any non-historic paint on the masonry. 3. To halt any deterioration of the masonry or make appropriate repairs. and 4. To check the condition of the masonry to ensure its integrity.

The nature of soil and debris on the building must be identified in order to select the proper method to remove it from the building in the most gentle way possible. This method should be the least damaging method to the building. A good example would be that soot and smoke must be removed with a different cleaning agent than that of metallic or oil stains. There are other issues to consider when cleaning including biological growth like molds and mildews and organic matters like tendrils that are left on the masonry after such things as ivy have been removed from the masonry.

Consider The Historic Appearance Of The Building

cracked paint on wooden wall surface

For paint removal, it’s vital to ensure that the paint is historically appropriate for such masonry. It’s also important to determine why the building was painted in the first place. Was it painted to conceal deterioration? Or, was it painted to protect softer brick or masonry? It may also have been painted as it was fashionable at the time to paint masonry. Regardless of the reason, it’s important to have an understanding of the reason that it was painted to understand the proper method of removal. If, for example, it was painted to stop deterioration, it may need to be removed differently than if it were painted to keep up with the fashion of the era. If the paint has been on the building for a long period of time, it may also require a different removal method than if it was only painted in the past decade.

Consider The Practicality Of Cleaning Vs. Paint Removal

It’s important to understand that gypsum or sulphate crusts may have melded together with the masonry and improper cleaning could net the result of removing the surface of the stone. In such instances, it may not be the right decision to clean the masonry. The removal of the paint may be seriously damaging to the masonry. It may be wiser to leave the paint on such masonry rather than destroy the original mason work. Older paint layers may build up to the extent that removing it may seriously damage the brickwork. Other times, it may be necessary to remove the paint so that newer paint will adhere properly to the brickwork.

Study The Masonry

While not always necessary, sometimes, it can benefit to research the type of paint and the specific colors old stone wall masonryused prior to attempting to remove the paint. By analyzing the very nature of the soil and dirt as well as the paint, it can be determined the best means of removal or if it needs to be removed at all. Professional consultants, as well as architectural conservators or conservation scientists or even preservation architects, can all be great assets to such a task. Consider historical district commissions or even preservation organizations as sources of information when making this determination.

Understanding The Building Materials

The actual construction of the building should be considered when determining the cleaning process. Inappropriate cleaning can have a disastrous effect on masonry as well as the other materials that make up the building. Masonry and other materials must be properly identified in order to properly determine the right method of cleaning. Distinguishing one kind of stone from another such as sandstone vs. limestone is important to the integrity of the cleaning process. What appears to be a natural stone may not be actual stone but rather concrete or cast stone and terra cotta may have been used in with natural stones. This is especially true for trim and upper stories of buildings so that they would stand out from a distance. Other important features may also appear such as decorative cornices, window hoods, entablatures, and others. They may be metal and not masonry at all.

Identify Any Prior Treatments

Previous treatments on the building and surroundings must all be researched as well. Maintenance records, as well as any other detailed information, should all be obtained in an effort to ensure the integrity of the building. If specific areas aren’t coming clean it’s important to do a closer inspection and note whether or not the discoloration is from dirt, from a water-repellent, or some other coating that has darkened over the course of time. Removing discoloration successfully may require different cleaning agents. Salts used to de-ice nearby sidewalks may have discoloured the building over the course of time. The cleaning may also attract the salts to the surfaces where they will appear to be efflorescence or powdery white substances on the building. This may require further treatment of the cleaning process in an effort to properly remove them. Always make proper allowances for tending to such potential setbacks when preparing to clean any historic building. Even if the building is only one type of masonry, different areas may require different cleaning solutions due to damage, environmental factors, and paint types used therein.

Choose The Right Cleaners

limestone wallIt’s very important to test the various cleaning methods and materials in an effort to choose the proper cleaning products that will do the least amount of damage to the building. Acidic cleaners can be potentially damaging to any acid-sensitive stones like limestone or marble. This can result in etching and dissolution of such stones. Other types of masonry may also suffer potential damage due to cleaning solutions that are incompatible to the particular type of masonry. There are various types of sandstone that require different solutions to retain their integrity. These will vary by geological location and should be carefully considered prior to cleaning. Even when the stones are properly identified, there may be unexpected impurities that can alter the results. Iron may react in a negative fashion with particular cleaning agents and sometimes, sandstone will have iron particles in the stone itself that may affect the overall results. Thus, having a complete understanding of the cleaning agents and how they will react with specific stones and agents is vital to retaining the integrity of the building.

Other materials may also be affected by specific cleaning agents. Many chemicals, for example, may be corrosive on paint and glass. Areas of the building that are more vulnerable may have serious deterioration that can be affected by these cleaning agents. Embedded ends of iron window bars, for example, may not be readily seen but may cause a serious chemical reaction that can affect the overall outcome of the project. Study the construction and ensure that there won’t be any surprises. Each project is a unique, one of a kind, project.