Masonry, particularly exterior masonry, gets sullied by different kinds of soiling. To keep masonry in tiptop shape, all surface deposits must be removed properly. Listed below are some of the types of soiling and the methods that may be employed to remove them.
For light industrial grime, a mild abrasive technique will do for cleaning masonry. This type of soiling can be removed with the help of hand brushes or mechanical ones. If mechanical brushes are to be used, bristle or bronze brushes are most recommended; steel brushes are not ideal for this type of cleaning job. Aside from brushes, water jets may also be used. Hot water and detergents can be effective in removing light grime from the masonry surface, but these should be tested first. Cleaning light industrial grime can be tricky, especially if the grime did not settle evenly on the surface. This is because it may be hard to do an even cleaning job.
Dealing with heavy industrial grime also poses a challenge. This is because this kind of soiling usually permeates the surface and reacts with the masonry. Alkaline gel is recommended for cleaning heavy grime, and should be used by strictly following the instructions provided by the manufacturer. Steam cleaning is also an effective cleaning method, ideal for the likes of strong cement render, concrete stone and hard stone (i.e. unpolished granite). However, cleaning should be immediately followed by repointing.
If the paint is in good condition and must be removed in its entirety, methylene chloride solution or caustic solution can be utilized; their gel forms can also be used. A hot air gun also works well for light coats of acrylic paint. Pressure cleaning with abrasive particles can also be effective, but this should be carried out carefully to maintain the quality of the masonry and pointing.
If the paint to be removed is peeling, gel removers with methylene chloride are the better option for cleaning. The paint can also be removed with hot air guns and manual scrapers.
The cleaning method required for graffiti mostly depends on the kind of paint used. For graffiti made with acrylic, alkyd or epoxy paint, cleaning can be done with paint remover and a bristle brush; a medium-pressure water jet is also effective. As for aerosol paint, it can be removed by scrubbing the graffiti with warm water and detergent solution.
The key to effectively removing graffiti from masonry is immediate cleaning after the graffiti was made. Test a small area first before proceeding. If the paint remover softens the paint film, cleaning must be restricted to the paint surface. Otherwise, paint removal must be done to the entire affected area.
Often, abrasive or alkali cleaning methods are employed to remove the likes of mould, moss & lichen. However, these do not properly address the problem of their growth. Steam or fungicide do a better job at eliminating the growth without damaging the masonry. It is recommended that the removal of moulds or mosses must be immediately followed with a durable toxic wash. The use of washes with copper, formalin and phenol are not ideal.
As for shrubs and ferns, herbicide works best for killing the growths. However, the removal may need to be followed with a repointing job. Before repointing, roots should be removed.
To prevent dealing with natural growths, masonry should be kept dry. Natural growths occur only when masonry is damp. If it is not possible for masonry to be kept dry, it should at least receive lots of sunlight to prevent dampness.
This kind of soiling can be eliminated from masonry with the help of a diluted orthophosphoric acid solution. If the affected masonry is marble, a 15 percent sodium citrate solution can be used.
Copper roofs and fittings can cause green stains on masonry through run-off. To remove the stains, the masonry should be washed with a diluted ammonia solution. It is important to be careful with the cleaning to prevent the solution from spilling onto unaffected areas.
The likes of pitch, tar and even chewing gum can be removed through the same methods. These kinds of soiling can be addressed by steam cleaning or mechanical scraping; these two are deemed as the most effective way of removing these surface deposits. These deposits can also be eliminated by freezing them with dry ice and chipping them off. Tar in particular may need to be washed with either hot water and detergent or organic solvents (with the use of a poultice).
Jessie Moore is the author of this article. This fulltime writer is currently a contributor for McIntyre Stonemasons Edinburgh.