Normal Techniques for Masonry
The basic technique established over many years has five stages carried out in order:
1. To pre-wet.
2. To degrease and prepare the surface for the acid cleaner.
3. To power jet off the surface debris.
4. To clean using the appropriate acid-based product.
5. To power jet off the surface debris.
The purpose of pre-wetting is to fill the pores in the masonry and mortar with water so as to prevent deep chemical absorption and retain the agent on the surface where its cleaning action is needed and from where it can be removed more efficiently later.
A cold-water jet is normally used and each square metre of surface washed and wetted for about 30 seconds after which a short time is allowed (5 – 10 minutes) for surface water to drain down. This jetting also removes dust and loose organic matter from the masonry face. This should be carried out on all
types of masonry except prior to using organic solvent-based paint stripper or silicone water
repellent or solvent based degreasers.
Therefore, specially designed primer mortars are available for the restoration mortars. The Remmers Primer Mortar ‘soft’ also has salt accumulating properties.
Surface Preparation & Degreasing
Prepare your walls properly before using an acid cleaner for the best results
If this stage is omitted, then the efficiency of the acid-based cleaner will be reduced and the results may be patchy. Heavy black surface carbon soiling may require repeated degreasing treatments or extended contact times and this will be evident from the first test patch trial. Care would be necessary regarding the contact times on sandstone etc. Hydrofluoric acid containing chemicals left on the surface of some masonry, for long periods, can lead to colour changes or to white deposits forming. Only weak acids are necessary for neutralisation on clean masonry or calcited stone.
For cleaning exterior masonry, we recommend a selection of one of the following:
These agents can be applied on any type of pre-wetted stone, brick or concrete etc., as shown in the table, following the safety precautions given in the individual product data sheets.
Thickened (viscous) products are applied by brush and worked well into the surfaces leaving an even and thick coating of the product.
Non-viscous products can be applied by low pressure spray units but considerable additional dangers are involved and so spray application is not a preferred technique.
Selection of Appropriate Acid Based Cleaner
It is always important to know what you are using before applying it to any surface.
Normally chemicals are applied to areas already wetted following a degreasing operation if not, then pre-wetting will be required before application of the acid based cleaner. Care must be taken. Acid based cleaners should not be used on calcited stone as this would have adverse effects on such stone. Frequently after degreasing the surface of calcited stone is then clean and only weak acid neutralisation (LC500) is necessary. On types of masonry which are more difficult to clean some contractors prefer to use stronger acid formulations with shorter contact times (eg SC100, RS250). Alternatively use the long contact methods where strong acids, such as Hydrofluoric, are not to be used.
Formulations containing Hydrofluoric acid should not be used on pre-cast concrete or normal concrete as white marks can be formed. These materials would however be cleaned by the normal degreasing process. It is recommended that acid cleaning agents be used as dilute as possible for efficient cleaning.
Acid Cleaning Products
The Protection of Selected Materials
Some chemicals can damage the surrounding surface you are cleaning
This covers the surface with a plastic film which can later be removed by peeling it off. The product is applied onto dry smooth surfaces by roller or brush, to form a complete film some 0.5 to 1mm in thickness. This protection is suitable for glass, polished granite, anodised aluminium and galvanised metal. It is not suitable for rough surfaces nor on UPVC. The coating will need to be replaced if longer than 6 months elapses.
Use waterproof adhesive tape and fix polythene sheets to this to provide a shield suitable for use on glass, polished granite, painted surfaces - aluminium, zinc and galvanised metals - but not for rough absorbent masonry.
Use a spray bar giving a fine water jet every 5 – 6 inches apart which washes continually over the surfaces to be protected. This is not normally used for glass or polished granite but is used where chemical run down and wash waters pass over calcited stone.