RESTORATION OF ANTIQUES AND HERITAGE MONUMENTS

The heritage monuments of a country are a testimony of the country’s architectural capabilities and evidence of its past, and hence, it is essential to preserve them for future generations. Whether the heritage monument is the Taj Mahal or The Shrine of Remembrance, they are important and the respective country has the responsibility to preserve these monuments.

Unlike other applications of sandblasting, the objective in restoration of heritage monuments and antiques is not to make the monument shine and look like brand new, but to clean and restore the natural finish.

This article gives you an overview of coatings and contaminants to be removed from the surfaces of antiques and heritage monuments, different methods of doing this, and the advantages of wet abrasive blasting or dustless blasting for the restoration of antiques and heritage monuments.

The coatings and contaminants that are to be removed from the surfaces of antiques and heritage monuments are stains due to pollutants (vehicle/industrial emissions), moisture in the air and birds droppings, weathering, soiling, algae, dirt, grime, wax, and more.

Let us discuss this briefly:

• Antiques and heritage monuments, especially heritage buildings are exposed to the atmosphere and get stains, weathering, contaminants in the air, pollutants from vehicle emissions and/or industrial emissions, bird droppings, dirt, grime, and many other contaminants on their surface. Even the antiques placed inside a building and the internal surfaces of heritage buildings can get dirt and contaminants on the surface.
• The ongoing deterioration of the stone used for building the heritage monument can create a layer of soiling on the stone surface that needs to be cleaned.
• The monuments may have stains due to moisture in the air, the build-up of wax, and the moisture on the surface can attract biological growth like algae and bacteria that can damage the finish and coating of thesubstrate.

Different methods used are:

Water cleaning: Water may be used for soaking the monument surface since it softens the layer of soil or dirt and it becomes easy to remove, and the soaking time depends on the coating to be removed. A high-pressure water jet can be used to clean the surface of the monument, but it is important to set optimum pressure to avoid damage to the monument. The hot water jet and steam jet may also be used.

The disadvantages of using water for cleaning are the water may seep into the monument (through joints or crevices) and create further problems, a high-pressure water jet is efficient for cleaning dirt and grime, but, it is not effective for removing tough coatings, and high-pressure washing can damage the substrate, chip away soft materials like limestone, and damage the inscriptions on the monument. Pressure water cleaning is also not effective for removing paint and rust deposits.

Chemical cleaning: The chemical cleaners used for cleaning the monuments are acidic or alkaline solvents suitable for dissolving the type of dirt and coating on the surface of the monument. The application of chemicals can be done using a spray and a suitable soft scrubber. The used chemicals are to be removed and washed clean from the surface of the monument. Chemicals may be efficient in removing the dirt and coatings from the surfaces of the monument, but it is harmful to the longevity of the monument, and not safe for the workers and the environment. This is a very slow process and takes a long time.

Detergent cleaning: The dirt and coating on the surface of the monuments can be cleaned using detergents. Compared to chemicals, detergents are less harmful to the monument, workers, and the environment. The application of the detergent can be done using a spray and a soft scrubber. The used detergents should be removed. However, this is a laborious and very slow process and has limited applications for cleaning dirt only.

Laser cleaning: Laser cleaning uses focused laser beams with high peak pulse power that is capable of removing a thin layer of contaminants. The laser energy is absorbed by the organic coating on the substrate and it evaporates, leaving the clean substrate behind. There is no damage to the substrate. Laser cleaning can remove paint, oil, and other contaminants, but its suitability for cleaning heritage monuments should be established by sampling before it is used. Laser cleaning technology is still nascent, very expensive and more importantly very slow and not suitable for large surfaces.

Dry sandblasting: Dry sandblasting is not considered suitable for restoring most heritage monuments as it is an aggressive process and can harm the monument, spread a lot of dust into the surroundings, and creates high level of noise disturbance.

Wet abrasive blasting: Wet abrasive blasting, also known as dustless blasting and vapor blasting, is one of the most environmentally friendly processes and works gently on the delicate surfaces of antiques and heritage monuments. This innovative technology has many benefits for the restoration of antiques and monuments and it does not harm the original surface. It is discussed in detail in the following section.

Wet abrasive blasting or dustless blasting involves mixing water and abrasive media inside a pressurized blast tank and combining it with compressed air to propel it onto the surface being blasted. Years of accumulation of dust, grime and growth can take its toll on the appearance of the monument. The impact of the blast force makes light work of removing the coating without damaging the surface. This technique is similar to dry sandblasting but the addition of water generates more impact and suppresses 95% of the dust. The blasting media and velocity can be varied according to the delicate nature of the monument (the material/stone used for the monument, the age of the monument, etc.).

It is good practice to do a sample in a discreet area to establish the parameters and the established method should be replicated for the remaining area.

Soda bi-carbonate: Soda bi-carbonate (Mohs hardness 2.5) is a soft single-use abrasive media and is good for removing dirt, grime, and mild coatings from the delicate surfaces of the antiques and heritage monuments. Soda bi-carbonate is efficient and does not harm the substrate.

Finely crushed glass: Finely crushed glass (Mohs hardness 5 to 6) is a good abrasive media for removing dirt, grime, and tough coatings from the surfaces of antiques and heritage monuments. The ratio of the media and water, and the blasting velocity (blasting velocity should start from the minimum) should be established by trial and error. The stand of distance can be manipulated to achieve good results. Recycled crushed glass is a waste byproduct making it environmentally friendly.

Fine grit glass beads: Fine grit glass beads is a rounded abrasive media (Mohs hardness 5 to 6) that works gently and efficiently for removing dirt, grime, and tough coatings from the surfaces of antiques and heritage monuments. As in the case of crushed glass, the ratio of the media and water, and the blasting velocity should be established by trial and error, and the stand of distance can be manipulated to achieve good results.

Things to be kept in mind when using wet abrasive blasting or dustless blasting for the restoration of antiques and heritage monuments:

• It is important to have a proper ratio of the abrasive media and water, and optimum blasting pressure to achieve good results.
• Manipulate the stand-of distance to achieve good results.
• The material used for the heritage monuments can be natural stones, red stones, marble, limestone, and many others. It is very important to study and understand the stones and other construction materials used for the monument before planning the correct combination of media and water, and blasting pressure.
• The restoration of the antiques and heritage monuments should be executed without damaging the original surface underneath.

• The advantage of wet abrasive blasting or dustless blasting is by properly adjusting the ratio of abrasive media and water, and blasting pressure, you can remove the coating from a delicate substrate like the surface of a heritage monument or a stubborn coating from a metal part.
• A wet abrasive blaster is a multi-media dustless blaster, consumes less abrasive media, and its low water consumption makes it environmentally friendly.
• Dustless blasting or vapor blasting is a preferred and perfect method for the restoration of heritage monuments and antiques since it works gently on their surfaces.
• Wet abrasive blasting is efficient and impactful as the water particles encapsulate the abrasive media and the saturated media creates a forceful impact removing the coating easily.
• The use of water suppresses the dust and makes it safe for the environment, the operator, and the others in the area.
• The advantage of dustless blasting is its ability to reach all nooks and corners of the monument.
• Wet abrasive blasting or dustless blasting can be used with different abrasive media such as soda bi-carbonate, finely crushed glass, and fine grit glass beads, based on the materials used for the monument and its age.
• The spray of the slurry that comes out from the blasting gun is even and there is no aggressiveness or harshness of the dry sandblasting in it.Wet abrasive blasting or mobile dustless blasting has mobility and can be taken to the place of the heritage monument.

The cost of using an inappropriate method of restoration can be huge. In trying to restore a monument to its old glory, there is a risk that one can do more damage and render the work unrecognizable or wreck a priceless treasure. For instance, a statue in Palencia, Spain, was restored in 2020 to reverse the damage from decades of weather erosion. The facade of a 1923 bank building on the Calle Mayor had a statue that depicted a smiling woman with sheep around her. But the restorer, used a dubious method and as a result left the statue’s face so disfigured that it has been compared to the face of a cartoon character.

The RapidBlastTM is the only Australian-made wet blasting machine and is manufactured and sold by Quantum Blast Australia. The Rapid BlastTM equipment is available in different sizes and can be tailored in different configurations and mounted on a purpose-built trailer or a truck to be fully mobile at a fraction of the cost of other foreign made alternatives. It is a versatile piece of equipment and very effective for many applications including the restoration of antiques and heritage monuments.

For more information on RapidBlastTMwet blast machine and mobile units please visit Quantum Blast at https://quantumblast.com.au/.

Phone: 1300822569 E-Mail: sales@quantumblast.com.au

When it comes to the restoration of antiques and heritage monuments, each monument is unique in nature and may need a tailor-made process for the best results. Wet abrasive sandblasting or mobile wet abrasive blasting is an efficient, and economical method for the restoration of antiques and heritage monuments and it works gently to retain the original surface of the substrate.