Vanadium stains normally appear on bricks 7 to 10 days after the Brickcleaner has completed the washdown of the walls. In most cases the change to the bricks brings about the need for a remedial treatment.
The following solutions will remove the Vanadium stains, testing on individual bricks will indicate the most effective.
The solutions are brushed or sprayed onto the dry bricks, no scrubbing is necessary, the solution will immediately remove the stain.
1. Household Bleach this can be tried first, as it is the cheapest remedy. Look for the percentage of Sodium Hypochlorite on the container, the higher the percentage the more effective the chemical.
2. Pool Chlorine this tends to be slightly stronger than bleach. Available in 15 litre containers, probably more economical than bleach.
3. Vango this is a proprietary cleaner which has been developed to remove vanadium stains. It is quite caustic and must be used with extreme care. Vango will damage painted and other finished surfaces if allowed to come into contact by overspray or splash, and not removed immediately.
4. Caustic soda this is an alkaline treatment, 100 gms per litre of water. Washing soda can be as effective, preparation the same.
Warning: The above alkalis are highly corrosive
5. Oxalic acid mixed at a ratio of 20-40 grams per litre of hot water. Hot water is necessary to dissolve the oxalic crystals. The solution is brushed or sprayed onto the affected bricks, when the stain has disappeared, complete the treatment by applying a solution of 10 grams of washing soda per litre of water. Allow this solution to remain on the wall. This neutralisation step is most important, it prevents unwanted further action by the oxalic acid.
The term efflorescence is given to a powdery deposit that forms on the surfaces of porous building materials such as masonry units, mortar and concrete. The temporary appearance of efflorescence is common on new masonry.
It is essential to first dry brush or scrub loose salt from the wall - hosing only will put most of the salt back into the wall.
The salts that appear as efflorescence can enter the wall from various sources. The masonry units, cement or sand may all contain salts; the atmosphere may carry sea spray in coastal areas, or sulphur acids i in industrial areas. Salt-bearing ground waters or garden fertilizers may be drawn into masonry below the damp-proof course. If damp-proof courses are faulty, salts from ground waters may pass into higher levels of the wall.
Efflorescence on new masonry may be unsightly, but it will not usually cause damage unless it persists for a long time. Persistent efflorescence may be a warning that water is entering the wall through faulty copings, flashings or pipes. If allowed to continue unchecked, the salts carried to the face of the wall may eventually destroy clay bricks which are lightly fired.
For efflorescence to occur three conditions must occur:
- (a) There must be salts present.
- (b) There must be water entering the masonry.
- (c) The masonry must be able to dry out.
The absence of any of the above three conditions will prevent efflorescence.
Any situation which allows water to enter the wall is likely to promote efflorescence. The most common causes are:
- (a) Poor copings and flashings.
- (b) Excessively raked joints which allow water to enter the bed face of the masonry (ironed joints are better).
- (c) The use of air entraining agents in the mortar which makes the mortar act like a sponge.
- (d) Poor storage of masonry units on site. Before units are placed in the wall they can absorb ground salts and excessive water in the stockpiled masonry, and can mobilize latent salts if they are present in the masonry.
It is desirable to store masonry off the ground and loosely covered with a waterproof membrane.
Efflorescence should be removed with a stiff dry brush prior to hosing.
Good laying practice and site procedures are the best guarantee for keeping a job efflorescence free.