Cleaning Lightly Colored/Slurry Bricks
The usual problem that occurs following cleaning of light coloured bricks is the appearance of vanadium stains on the bricks seven to ten days after the cleaning has been completed.
Although many brickcleaners exercise care during cleaning, the vanadium stains will still appear, mainly as a result of the saturation of the walls and the slight acid residue that will be left in the bricks.
In most cases it is this slight acid residue which is the cause of most (if not all) secondary staining. Although neutralising the walls after cleaning is not everyday practice, it is now becoming clear that a neutraliser should be included in the final washdown after cleaning. This neutralising treatment should be carried out for all bricks, regardless of colour, not just light coloured bricks.
This cleaning procedure is written to assist brickcleaners to minimize the incidence of vanadium staining appearing after the acid wash. No guarantee can be given that vanadium will not appear after cleaning, as the chemical strength, site and weather conditions and experience and expertise of the operative carrying out the cleaning is unknown.
It must also be remembered that vanadium is part of the clay body of most light coloured bricks, and that an incidence of staining does not indicate a defect or any type of problem with the brick. Vanadium stains are very easy to remove and this must be taken into account when planning the cleaning procedure for all light coloured bricks.
Please read the accompanying page on Remedial Treatments.
Caution: Vanadium stains can sometimes be present on light coloured bricks before the cleaning commences, this results from the brickwork becoming saturated from heavy and/or prolonged rain. Work practices today do not include protecting unfinished walls from overnight rain, so the incidence of this type of staining is becoming more prevalent. Prior to cleaning these stains must be removed by applying Oxalic acid solution to the walls. This will avoid the possibility of stains becoming 'burned' or 'set' on the bricks and quite difficult to remove.
Four steps should be followed as the cleaning procedure for light coloured bricks
- Fully wet down wall area to eliminate suction
- Apply cleaning solution 20:1 strength maximum
- Wash down wall areas to remove mortar debris
- Apply neutraliser in final rinse
1. Wetting down wall areas is important, acid must not be allowed to be absorbed into the bricks during cleaning, as this will result in some form of secondary staining occurring as the bricks dry out.
Break up the walls into manageable sections, approximately 10m2, working on the shaded side to avoid premature drying. Complete each section in turn, leaving the neutralising treatment until the wall areas are finished.
2. Hydrochloric acid is still the normal choice for most brickcleaners, but for light coloured bricks the acid/water strength must be modified.
20 parts water to 1 part acid should be considered the maximum strength solution for light coloured bricks, and if the job is very clean, even weaker solutions should be considered.
CSR Building Materials recommend Noskum as the preferred cleaning solution for light coloured or slurry bricks and where possible this solution should be used in preference to hydrochloric acid. This can further assist in inhibiting the appearance of vanadium stains after cleaning. Where the Hydrochloric acid is applied through a Venturi, which normally delivers 10 to 1 solutions, the 15 litres is split into 2 containers and then topped up with water in each. This effectively reduces the acid solution strength to 20 to 1 without any further modification.
The acid solution should be applied to the wall when it is still wet, this is most important as no acid should be absorbed into the wall.
The solution should be allowed to remain on the wall from 3 to 5 minutes.
This should be sufficient time for the cement to be softened ready for the washdown stage.
3. The softened mortar can now be removed using high pressure water.
1000 lbs per sq inch is the recommended maximum in the Industry Code of Practice. A 15 degree fan jet is recommended to wash off the softened mortar, while avoiding any damage to bricks or mortar joints.
The wash down should be carried out, commencing at the top and working methodically down the wall, making sure that no bricks are missed, cleaning each course in turn and finishing at ground level.
The fan jet should be applied at an angle of 25 to 30
degrees, about 450mm from the wall.
4. When the washdown has been completed, commence application of the neutralising solution. The solution is made up of the following proportions:
100 grams of Sodium Carbonate to 5 litres of water.
The walls should be flooded with the solution, best results are possibly obtained using a low pressure sprayer. A back pack type sprayer is suitable.
"Flooding" the wall simply means wetting the wall to the point where the liquid runs down the wall.
Using the above procedure and chemical strengths should reduce or eliminate the incidence of vanadium staining. As stated previously, this is not a guarantee as the cleaning operation is being carried on outside
CSR's control. CSR Building Materials offer this cleaning advice, but remind all customers that the final responsibility for any brickcleaning procedure carried out using acidic cleaning solutions remains with the Brickcleaner.