Case 5
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Maintenance and Diagnostics
Maintenance
Masonry requires periodic maintenance to ensure its continued successful performance.
Although the brick units are quite durable over time, other materials in the wall system will require periodic repair and/or replacement.
Typical maintenance items which should be addressed are repairing of cracks in masonry, cleaning clogged weep holes, removing stains and efflorescence, repainting steel, replacing caps or copings, repointing mortar joints (tuckpointing), replacing deteriorated sealants and caulking, and cleaning the masonry.
Cleaning Existing Masonry
There are four cleaning techniques for existing masonry.
Cleaning to external brickwall of public residential flats is rarely carried out.
Scheduled repainting of once every five years is adequate in combating dirt stains and keeping the buildings in an acceptable state of cleanliness. Table 1 shows the cleaning method for each type of stain.
| Condition of Brick wall | Cleaning method |
| Dirt on brick Smooth textured bricksModerately rough texture Very rough texture Walls with coloured mortar joints | Scouring powder and a stiff brush. Where budget allows, high pressure steam (< 60 psi) with detergent allows faster cleaning. Scrubbing with an oxalic acid-ammonium biflouride solution Pressurized water cleaning (< 700 psi) Mild detergent solutions. Acids may bleach coloured mortar. |
| Biological stain | Apply sulpharnate or weed killer. |
| Green Stains from Vanadium salts | Flush brickwall with water followed by solution of potassium or sodium hydroxide. Allow it to stand for 3 days. Hose off remaining white salt on the brickwall from the hydroxide. |
| Paint on wall | Chemicals and high-pressure steam or scrubbing with steel. wool. |
| Walls with efflorescence | Generally disappear with normal weathering. Can be removed by dry brushing or with clear water and a stiff brush. Heavy accumulation requires proprietary cleaner. |
| Grayish- white haze (White scum) | Masking by solutions of paraffin oil and Varsol, or linseed oil and Varsol, applied by brush to the affected brick units. |
Table 1: Cleaning method
Diagnostics of Defect (see also NDT)
Finding the source of water ingress into the facade system is most crucial. The following methods are recommended:
Thermography can be used to identify the position of cracks. A range of crack widths, representing mechanical damage, has been induced under controlled laboratory conditions. The method is based on the characteristics of heat flow phenomenon, in a conductive medium of specific geometry, which is intended to model predetermined boundary conditions.
Microwave tomography is a technique to measure the moisture of various materials based on the relatively high dielectric constant of “water” in comparison to the dielectric properties of the material. An electrical field (microwave) is applied to the material, and the microwave induces oscillations of bipolar molecules (i.e., water). Water molecules will reflect and absorb an electrical field during oscillations. A higher electrical field reflected indicates higher water content.
The technique is non-destructive and applicable to wood, brickwork and concrete. The uniqueness of this technique is its ability to measure moisture content at various depths up to 110 mm, allowing the plotting of a 3-D contour of moisture content and facilitating the tracing of the water source.
