GB2147346A

GB2147346A - Drying damp masonry

Info

Publication number: GB2147346A
Application number: GB08424727A
Authority: GB
Inventors: Klaus Beyer; Hubertus Birkenhofer; Peter Friese; Kurt Stepper; Gerhard Hippel; Klaus Reckin
Original assignee: Bauakademie der DDR
Current assignee: Bauakademie der DDR
Priority date: 1983-10-04
Filing date: 1984-10-01
Publication date: 1985-05-09
Also published as: FR2552797B3; IT1179139B; DE3430450A1; GB8424727D0; SU1416635A1; FR2552797A1; IT8467983A0; DK473684A; GB2147346B; DD231236A3; NL8402688A; BG45876A1; BE900746A; HUT39807A; IT8467983A1; DK473684D0

Abstract

Apparatus for reducing dampness in masonry using a combined electrode, consisting of a plastic shell (1), a steel bar (2), a cover plate (3). a discharge aperture (4), and burnt lime (6). The apparatus provides a combination of a number of effects such as chemical and hygroscopic affinity of the burnt lime to water, accompanied by the electrolytic decomposition of the water, electrolytic movement of the soluble salts present in the masonry and electrosmotic movement of the water. At the same time calcium ions are introduced into the masonry and consolidate it. <IMAGE>

Description

SPECIFICATION Apparatus for drying damp masonry The invention relates to an apparatus for drying masonry affected by dampness, particularly in residential dwellings.

As is known, horizontally laid damp courses technically come to the end of their life after forty to fifty years and cease to be effective. In principle, a large number of processes have been described in literature for renewing the damp course in old buildings. These methods can be subdivided as follows: (1) Mechanical processes which cut the masonry and use a sealing pasteboard or plastic foil to obtain a renewed horizontal seal. These processes are usually very reliable but generally involve hard physical labour or permanent interference with the structure of the building. If the masonry is highly salinized their effect is very limited.

(2) Chemical injection processes, in which by a great variety of techniques a liquid and/or suspended sealing composition is introduced into the masonry. Processes of this kind generally consume considerably quantities of sealing substance and are very cost-intensive as well as being technically no longer reliable when used in masonry of a mixed type, owing to the unsatisfactory distribution of the substance.

(3) Electrochemical processes, in which by the aid of electro-kinetic phenomena a drying operation is effected. These methods must be subdivided into active and passive types. The greatest problem in the case of active methods is the stability of the electrodes over a period of twenty years or more, unless precious metal electrode material (such as platinum) is used. The cost cannot however be justified.

The electro-osmosis methods, in particular, have gained an unfavourable reputation in the past as the promised drying effect has failed to materialise.

With certain processes it is recommended that electro-osmosis should only be used where a certain soluble salt content in the masonry is not exceeded.

In actual fact the presence of soluble salts in the masonry represents a serious problem.

Owing to the circulation of the water in the masonry the salts penetrating the masonry with moisture from the soil accumulate in the evaporation zone. Efflorescence of this kind is well known. These salts vary in their composition and this depends first and foremost on the nature of the soil at the building site and also on the salts present.

Salts normally present such as Mg Cl2, Ca Cl2, Na2SO4, have hygroscopic properties and also accelerate the rise of the water on the osmotic principle. Above all, however, these salts impede the osmotic drying process. The anions present in the masonry migrate to the anode where they are discharged thus causing considerable corrosion of the electrodes by chemical reactions. This known fact has so far not been sufficiently taken into consideration.

With certain anode materials such as graphite, the electrode corrosion processes may lead to a change in the pH value and hence in the zeta potential. thus replacing the desired sealing effect by a pumping action.

DEA 24401 92 describes a process and an apparatus for the stabilization of the soil by means of burnt lime. Holes are bored in the foundations and filled with burnt lime. The water in the adjacent soil is thus removed.

DEA 24401 92 relates to a process and apparatus for active electro-osmosis. For this purpose electrodes made from material with a high carbon content are introduced into the masonry and connected up to a D.C. source.

DEA 2717291 relates to a process for drying out by means of D.C., passing through the masonry via the anode and cathode, the anode consisting of a plastic or pasty substance provided with an insulated accompanying conductor.

Further known processes do not provide for the desalination and simultaneous drying of masonry damaged by damp.

An object of this invention is to provide an apparatus by which damp masonry can be rapidly dried thus enabling old buildings to be restored in value. The apparatus enabling soluble salts to be removed from the masonry chemically and electrolytically and at the sime time increasing the calcium cation content of the masonry thus to dry it by electro-osomotic means.

According to this invention there is provided apparatus for drying damp masonry by means of an electro-osmotic process with electrodes provided in holes bored in advance in the masonry, wherein the holes slant outwards and a trough is provided in each hole, which also contains a substance which has a chemical and physical affinity with water in which substance an electrically conductive bar is embedded, the bar passing at a point of entry, through a cover plate housing a recess, the bar having no direct contact with the masonry.

In this arrangement holes bored in advance and slanting outwards contain a substance having a chemical and also physical affinity with water, preferably burnt lime in a ground state, a trough being provided between the masonry and the said substance. An electrode, preferably a steel bar, is embedded in the substance and passes through a cover plate having a recess underneath. That end of the electrode which is present in the masonry is likewise surrounded by the substance with the cover plate situated in the zone of the outer edge of the masonry to be dried.

The method is characterized by the ease with which the apparatus can be installed, the rapidity of operation and the partial re-use of the electrodes. The method is suitable for all building styles and building materials but is mainly suitable for masonry which has developed an excessive salt content.

The invention is described in more detail with reference to an example and the accompanying drawings, in which: Figure 1 shows a cross section through the electrode, and Figure 2 shows an exampie of an installation of the apparatus.

A single dwelling house which has been subject to damp for a number of decades and with a high salt content and up to 25% by mass of moisture in a basement area was selected to be desalinated and dried by means of the apparatus according to the invention.

For this purpose, holes of 45mm in diameter and 150mm in depth and 700mm apart were bored beneath the basement ceiling. The bores were filled with pulverous burnt lime using pneumatic pressure. The combination electrode (see Fig. 1) was then suitable inserted. A steel bar 2 serving to provide the contact with the masonry 5 (Fig. 2) was pushed through the cover plate 3 into the masonry 5 to a distance required to ensure that it would be surrounded on all sides by lime.

After five days a solution of CaCI2 and Ca(OH)2 passes out through the discharge aperture 4.

At this time the burnt lime 6 is quenched and of a pasty consistency.

At the beginning of the discharge of the solution through the trough 1 and by means of an adjustable rectifier a voltage of 40 V is applied to the anode system and connected to two earthing bars which are arranged as a cathode. At the commencement of the desalination and drying a current of 280 mA flowed, decreasing to 40 mA after six weeks.

During this period the following desalination and drying were achieved: Initial After Measurement: six weeks H20 content above basement floor 18.8% by mass 9.2% by mass H20 content 1.0 m above basement fioor 23.9% by mass 5.8% by mass H20 content Underneath basement ceiling 24.9% by mass 4.2% by mass Chloride content, based on total masonry 0.029% 0.007%

Claims

1. Apparatus for drying damp masonry by means of an electro-osmotic process with electrodes provided in holes bored in advance in the masonry, wherein the holes slant outwards and a trough is provided in each hole, which also contains a substance which has a chemical and physical affinity with water in which substance an electrically conductive bar is embedded, the bar passing at a point of entry, through a cover plate having a recess, the bar having no direct contact with the masonry.

2. Apparatus in accordance with Claim 1, wherein the length of the trough and the bar is greater than the depth of the holes in the masonry.

3. Apparatus for curing dampness in masonry substantially as described herein and exemplified and with reference to the drawings.

4. A method of reducing damp in masonry carried out substantially as described herein and exemplified.