GB2205497A

GB2205497A - Process for controlling growth or organisms on masonry

Info

Publication number: GB2205497A
Application number: GB08709588A
Authority: GB
Inventors: C Y Reed
Original assignee: NEOLITH CHEMICALS Ltd
Current assignee: NEOLITH CHEMICALS Ltd
Priority date: 1987-04-23
Filing date: 1987-04-23
Publication date: 1988-12-14
Also published as: GB8709588D0

Abstract

A process for controlling the growth of organisms on masonry comprises the application of a first aqueous solution of a heavy metal compound, such as copper acetate, to the masonry and allowing the solution to penetrate into the masonry. An aqueous solution of a second compound, for example sodium hydroxide, may additionally be applied, in order to react with the first solution and so produce a third compound, the water solubility of which is less than that of the first or second compound. Such a process may kill organisms growing on masonry and/or retard or prevent further growth of organisms over a long period of time.

Description

PROCESS This invention relates to a process for the control of the growth of organisms that cause# unsightly deposits on and/or deterioration of building structures, and the prevention or retardation of further growth thereof.

The process is particularly suitable for the treatment of masonry, by which term is included brickwork, stonework, either natural or artificial, concrete and rendering. By the term "organisms" we include algae, lichens and mosses and/or bacteria. Whilst the invention is described specifically for the treatment of masonry, this is not meant to limit the scope of the invention.

It is not unusual to find that surfaces of building structures which, for various reasons, retain water for periods of time, develop an organic growth which frequently discolours the structure due to the colour of the organism itself, for example they turn green, or to the colour of excretions produced by the organism. This discolouration of masonry is also not uncommon on masonry surfaces which have been cleaned using chemical, wet grit blasting or pressure water washing and furthermore, organisms producing acidic excretions, may bring about structural damage of their substrates.

Numerous formulations have been proposed for controlling the growth of organisms on masonry (see the Building Research Establishment Digest 139, 1982 edition), but the majority of them are expensive and frequently involve the use of water soluble or volatile chemicals which will be adversely affected by rain or warm weather, or if applied from organic solvents, have the disadvantage of expense, possible flammability and toxicity, of the solvents. Agents effective in the vapour state will be more volatile in warm dry weather which is the period of less active growth for algae and mosses, whereas the effective agents which are the subject of this patent application would not be depleted in warm dry conditions. A much simpler formulation uses sodium hypochlorite, but whilst this is effective in killing the organism, it does not provide any long term protection against further growth.

There is therefore a need for a simple and cheap process for the treatment of masonry which will not only kill any organism which may be growing on the masonry, but also retard or even prevent further growth of organisms over a prolonged period of time. We have nowfound that the application of aqueous solutions of compounds of the heavy metals, preferably compounds of lead, mercury and bismuth, and particularly compounds of copper, are effective in killing organisms present on masonry, and retard further growth.

Therefore, according to one embodiment of the present invention, there is provided a process for the control of the growth of an organism in which an aqueous solution of a compound of a heavy metal is applied to the surface on which the organism is growing and is allowed to penetrate therein. Preferably the metal is lead, mercury or bismuth, and desirably copper.

Preferably thick or heavy surface growths should be removed from the face of the materials to be treated first using for instance a phosphor bronze brush then the aqueous solution of the metallic compound may be applied to the surface by any convenient method, for example by brushing, spraying or by use of a high pressure jet.

The rate of application of the solution should be such that there is an excess of solution on the surface to enable it to penetrate through any growth which may be present, and also to be absorbed into the structure, e.g.

masonry. It has been found that good protection is achieved when a 2% to 4% weight percent of solution of the metal compound is applied at a rate of 2 litres per 4 to 5 sq.metres of surface, but these values may vary according to the nature of the particular surface to be treated.

For the treatment of masonry according to the present invention, any waterfsoluble compound of a heavy metal may be used, but the simple, water soluble salts are to be preferred. Some compounds may be preferred to others. Thus, for certain applications, it may not be desirable to use sulphates, because of the general belief that sulphates may lead to the formation of white encrustations on the masonry surface or lead to a weakening of the masonry structure. Solution of nitrates are not particularly desirable because of the tendency of the nitrate ion to support the growth of algae. We have found the use of acetates, in particular copper acetate, to be quite effective.

Treatment according to the present invention of masonry having a growth on its surface not only kills the organism responsible for the growth, but also prevents further growth over a period of months due to the slow leaching out of the metal compound by weathering, e.g. by the action of rain. This period during which further growth is prevented may be lengthened by converting the metallic compound absorbed into the masonry structure into a compound of reduced water solubility by the application of a second aqueous solution.

Therefore, acccording to a further embodiment of the present invention there is provided a process for the control of the growth of an organism in which an aqueous solution of a first compound of a heavy metal is applied to the surface on which the organism is growing, and after sufficient time to allow the compound to penetrate therein, an aqueous solution of a second compound is applied in sufficient amount to react with the first compound to form a third compound whose water solubility is less than that of the first compound.

Preferably the second compound is a carbonate, bicarbonate or hydroxide, for example sodium carbonate, sodium bicarbonate, sodium hydroxide and ammonium carbonate and ammonium hydroxide. The second compound is applied as an aqueous solution, and preferably at a concentration of 5 to 6 weight percent. This solution may be applied to masonry after a period of 3 to 24 hours after the application of the first solution, depending upon the porosity of the masonry. After the application of the second solution, the dried surface may be water washed to remove any surface deposits which may appear, using non-acidic washing media or jetting fluids, e.g.

towns water.

When the second compound is a carbonate, bicarbonate or hydroxide, the first compound is converted into a third compound which is slowly and effectively leached out of the masonry by the action of acidic rain to provide protection against growth of organisms over an enhanced period of time.

It will be realised that in the processes described above a mixture of compounds may be used. thus, the surface on which the organism is growing may be treated with two or more compounds or a heavy metal which may be applied as a mixture, or may be applied separately and sequentially. Similarly, after the application of the heavy metal compound or compounds the surface may be further treated with 2 or more reactive compounds which may be applied as a mixture or may be applied separately and sequentially.

Where it is desired to combine the application of a chlorinating agent, e.g. sodium chlorite, with the process of the present invention, the pH of the application liquid must be carefully controlled to prevent destabilisation of the chlorinating agent and conversion of the metallic compound into an insoluble form before its application into the masonry. Thus when the chlorinating agent is a solution of sodium chlorite and the salt is copper, the pH of the chlorite solution should be adjusted to a pH of 4.5 to 6.5, preferably 6, before the copper salt is added.

Claims

CLAIMS:

1. A process for controlling the growth of organisms on a surface, comprising the application to the surface of an aqueous solution of a compound of a heavy metal and allowing said aqueous solution to penetrate into said surface.

2. A process according to Claim 1, wherein said heavy metal is selected from the group consisting of lead, mercury, bismuth and copper.

3. A process according to Claim 1 or 2, wherein thick or heavy surface growths are removed from the surface by use of a phosphor bronze brush prior to the application of the solution.

4. A process according to any of the preceding claims, wherein said aqueous solution penetrates into the surface.

5. A process according to any of the preceding claims, wherein a 2 to 4% by weight solution of the heavy metal compound is applied at a rate of 2 litres per 4 to 5 square metres of surface.

6. A process according to any of the preceding claims, wherein said heavy metal compound is a substantially water soluble simple salt.

7. A process according to any of the preceding claims, including the further step of applying sufficient of an aqueous solution of a second compound to react with the first mentioned compound to form a third compound the water solubility of which is less than that of the first mentioned compound.

8. A process according to Claim 7 wherein the second compound is selected from the group consisting of a carbonate, a bicarbonate and a hydroxide.

9. A process according to Claim 7 and 8 wherein the second compound is applied as a solution of 5 to 6% by weight concentration.

10. A process according to Claim 7 to 9 wherein the second compound is applied within a period of 3 to 24 hours after the application of the heavy metal compound.

11. A process according to any of the preceding claims wherein a chlorinating agent is applied with the solution of the heavy metal compound.

12. A process according to Claim 11 wherein the chlorinating agent is a chlorite salt.

13. A process according to Claim 11 wherein the solution of the chlorinating agent is adjusted to a pH value of 4.5 to 6.5 before a solution of a heavy metal compound is added.

14. A process according to any of the preceding claims, wherein the surface is a masonry surface.

15. A surface whenever treated by a process according to any of the preceding claims.

16. A process for controlling the growth of organisms on a surface, substantially as hereinbefore described.