How to Repair of Rising Dampness in walls of Ground Floors in Buildings?

How to Repair Rising Dampness in walls of Ground Floors in Buildings Constructed without DPC? and How to Repair Efflorescence in Buildings?

Introduction

The plinth is the portion of the wall of a building immediately above ground level to the ground floor level. This height usually ranges from 45 cm to 100 cm. Nowadays, in building construction, we provide a beam at the lower or upper level of the plinth, called the plinth beam. It is usually 10 cm thick with at least 6 mm rods spaced at 10 cm at the top and the bottom and 6 mm stirrups at the rate of 23 cm. (This is in addition to the grade beam or ground beam we provide at the foundation level for isolated footings, under reamed piles, etc.)

In all buildings, nowadays, we build a damp-proof course (DPC) to prevent dampness from going up the walls from the foundation due to the capillary action of groundwater. The damp-proof course can be on the plinth beam or on a beam built separately always above the ground level. If it is built separately, it should be at least 40 mm to 50 mm thick and should have 1:2:4 concrete with a waterproofing compound. Over this, we paint a thick layer of bitumen to prevent water from rising from the wall from the foundation. A much cheaper way for low-cost buildings is to put only a 1:3 cement mortar layer with bituminous paint (or a bituminous membrane placed over it) in a portion of the wall above the ground. This should be provided for all walls, i.e., external, and internal walls. Thus, DPC prevents water from rising from the wall from the foundation by capillary action. Even though in all the new buildings, nowadays, we place the DPC, in old buildings like old assembly halls, old church buildings, and old residences, these are absent. How we prevent moisture migration in these old buildings where DPC has not been provided is the major problem dealt with in this article.

 

Methods to Rectify Dampness

The following methods are usually recommended:

1. Construct a new DPC (Note: Conventional type consists of 40 mm to 50 mm thick cement concrete in the proportion of 1:2:4 with water-proofing compound.)

2. Pressure injection or gravity feeding of a suitable chemical solution within the plinth (Water soluble silicon solutions are commonly used.)

3. Pressure injection of resin mortar in boring holes

 

Construction of New DPC

For installing a DPC in an old building that has been built without DPC, we cut the mortar bed joint of two brick courses above ground level in stages of about one meter in length at a time. No two adjacent lengths should be repaired consecutively. A new DPC with a waterproofing compound can be inserted with the rebuilding of the removed brick course. This method is too slow and may lead to structural settlement and cracking of walls if the walls are weak. Hence, the methods described in the subsequent section are usually recommended.

 

Method of Injection of Chemicals (Silicon)

Another method of repair is the injection of chemicals as a liquid. The most common method used for placing DPC is based on injecting water-soluble silicon (which has the moisture-resisting property) into the brickwork, as shown in Figure below.

Pressure injections of chemicals 

Note: Silicon paints are the ones usually used for external waterproof painting and to prevent rainwater from seeping into walls and wetting the exterior walls. We introduce the chemicals by one of the following methods:

1. Pressure injection

2. Gravity feed

 

Pressure Injection

Old plasterwork etc. on the surface of the wall is removed along the length of the wall, at least 30 cm (3 to 4 brick courses above the ground. Holes of 12 mm diameter are bored into two-thirds the width of masonry at approximately 150 mm horizontal intervals. These holes should be slightly inclined downwards. The chemical solution such as polyurethane injection resin or gel is injected by a pressure pump until it extrudes from the masonry. We usually use high-pressure injection (0.3 MPa to 0.7 MPa) for solvent-based solutions and low-pressure injection (0.1 MPa to 0.3 MPa) for water-based solutions. The holes are finally closed with waterproof mortar.

 

Gravity Feed

A simpler gravity feed method can also be used to treat the rising dampness (Figure below) For this method, we use larger holes having 25 mm diameter. Chemicals such as dilute silicon are transfused from the containers with feed tubes inserted into the holes. Then, the liquid is allowed to flow till the masonry gets saturated.

Figure: Gravity infusion of silicon in solution.

An alternate solution is to freeze the chemicals into pellets and place them in the holes. They melt and disperse into the masonry. It is to be continued till the wall section gets saturated. The holes are finally closed with waterproof mortars.

 

Pressure Injection of Resin Mortar

Another method is to inject a special mortar. It can be used for preventing rising dampness. We bore 20 mm to 30 mm diameter holes from both sides of the walls to a depth of three-fifth of the wall thickness. These are 30 mm apart and inclined downwards at 20° to 30°. Flush out the drill holes and inject the special mortar from the base of the hole upwards using hand operated caulking gun. This mortar is composed of special cement mortars containing styrene-butadiene resin (SBR) or epoxy resin, mixed according to the instructions given by the manufacturers. This resin hardens to an impervious layer and prevents the migration of moisture.

 

Efflorescence in Walls of Buildings

Efflorescence is different from rising dampness. Efflorescence is the formation of the white crystalline substance that appears on brick walls surfaces due to salt in the brick or sand or the water used in its construction. When the walls get wet and then, dry out, the dissolved salts come to the surface through the pores. The salts can also absorb water from the atmosphere and form ugly patches on the wall. Usually, efflorescence can appear above the floor or below the roof or other places of the building where the wall can become moist by capillary action or leakage of water.

 

Measures should be taken during the construction of walls so that there will be no salts present in the materials used. We should also provide a damp-proof course (DPC) that prevents moisture from going up the walls. Many old buildings do not have the DPC. Similarly, rainwater should not be allowed to moisten the walls.

 

Our problem is now the maintenance of a wall with efflorescence while retaining a good shape. For this, we should prevent the water from entering the brickwork. If the salts have already been deposited on the surface of the wall due to past negligence, we should first remove the plaster and scrub the surface with a brush to clean the surface of the salts. Then, we may clean the wall with a solution of mild hydrochloric acid (1 part of acid + 5 parts of clean water). The surface is then thoroughly cleaned with a wet brush and then, plastered, and dried. No dampness due to rainwater from nearby storage tanks or leakage of the water supply or drainage system should wet the wall again so that the salts present inside are not brought to the surface.

 

Conclusion

The rising dampness in the walls of ground floor rooms of old buildings can be reduced considerably by injecting silicon or resin into the walls above the ground level. It acts as a DPC for the wall. Efflorescence can be stopped by removing the source of wetness and cleaning the deposits that have already been deposited. No further wetting of the wall should be allowed.