Masonry Magazine March 1971 Page. 17
20
on Brick&Tile
REVISED
Construction
Technical Notes CB
©STRUCTURAL CLAY PRODUCTS INSTITUTE 1750 OLD MEADOW ROAD, MCLEAN, VIRGINIA 22101 PHONE 703 893-4010
INTRODUCTION
CLEANING CLAY PRODUCTS MASONRY
GENERAL RECOMMENDATION
MAY
1964
The appearances of many masonry structures have been irreparably marred by improper cleaning. In many instances, damage caused by faulty cleaning techniques or the use of the wrong cleaning agent cannot be repaired, short of replacement. Many such instances have been brought to the attention of the Structural Clay Products Institute during the past twenty years which can be attributed to one or more of the following:
1. Failure to thoroughly saturate the masonry with water prior to the application of the cleaning agent, particularly when an acid solution is used. This permits absorption of the cleaning agent by the masonry unit and the mortar joint, and may result in "mortar smear" or the development of efflorescence or green stain on the masonry unit.
2. Use of a too-strong acid solution. Such a solution has a tendency to discolor masonry units, particularly the lighter shades, and produces an appearance frequently termed "acid burned". It also promotes the development of green or brown stain.
3. Failure to protect windows and trim. Most cleaning agents, particularly acid solutions, have a corrosive effect on metal and, if permitted to come in contact with metal window frames, will cause pitting. These agents are readily absorbed by many trim materials, such as limestone and cast stone, and the staining resulting from this absorption cannot be removed, other than with abrasives.
The following discussion will cover six general classifications which include most of the cleaning problems of clay masonry.
1. Cleaning new construction to remove mortar, mortar stains and any other material, such as dirt, deposited on the masonry during construction.
2. Removal of efflorescence.
3. Removal and prevention of vanadium stain.
4. Removal and prevention of manganese stain.
5. Removal of stain from external sources, such as from metallic or organic substances where, as a rule, relatively small areas are affected to which special treatments may be applied.
6. Cleaning old buildings.
Minute quantities of certain minerals found in some burned clay masonry units will react with some cleaning agents, particularly acids, and cause staining. Since the reactions cannot be predicted in advance, it is recommended that, before applying any cleaning agent to a masonry wall, it be applied to a sample wall section of 10 to 20 sq ft and its effectiveness judged from an inspection of the sample after a period of not less than one week after application.
CLEANING NEW MASONRY
In the construction of masonry walls, a skilled mason will generally keep the surface remarkably free from mortar particles and stains. However, in modern construction, where speed in erection is important, even the most skilled mason will find it difficult, if not impossible, to keep his work entirely free from stains. For this reason, most specifications require a final washing down of all masonry work.
a. Acid Solution. In the past a solution of hydrochloric acid has been used most extensively as the cleaning agent for new masonry. The following procedures utilizing an acid or base solution are reproduced from the publication, Brick Cleaning, by J. L. Clark, published by the Robinson Brick and Tile Company, Denver, Colorado, and are recommended as good practice.
Cleaning Dark Brick (Red, Red Flash, Brown, and Black). Dark colored brick are most apt to show a light grey mortar scum from failure to rinse off all dissolved mortar and dirt. Brown and yellow discolorations will also show.
Procedure A. Requires no acid. (Acid should be used only in difficult cases or areas.)
1. Make the cleaning operation one of the last phases of the job. Don't start before mortar is thoroughly set and cured.
2. Dry clean-remove large particles of mortar with wood paddles and scrapers before wetting the wall. In some instances it may be necessary to use a chisel or wire brush.
3. Presoak wall. Saturate the masonry with clean water and flush off all loose mortar and dirt.