With climate change and rapid urbanisation, incessant rains and flooding are some of the biggest problems that are prevalent in cities today. Obstruction of pathways along water canals, ineffective drainage systems, broken dams, and overflowing rivers are some of the reasons for the flooding. And these floodwaters bring insects, viruses, and diseases with them. Moreover, water entering residential buildings forces residents to move out as the building poses a threat of disintegration. To tackle this problem, this is the first post of a series that will inform people about the adverse effects of flood water damage and shed light on the emergency building repairs that can be used to stabilize them.
The article will talk about the causes, prevention, and repair of buildings affected by flooding.
List of Contents
1. Foundation
1.1 Damages to the Foundation
Foundation is the first part of the building component to get affected by flooding. The earth under a foundation may get displaced due to water flow and soil erosion that happens during both the initial flooding and when the water recedes. This leads to a failure in the foundation - in such a case, it is important to rebuild the damaged areas and walls with a larger base in order to bear the load, as a failure in the foundation might lead to permanent damage or collapse of the building.
1.2 Drainage Around the Foundation
It is necessary to make sure that the rainwater flows away from the building, by creating the required sloped pathways. The earth which was collected close to the foundation during the floods must be removed and a substantial level difference between the external and the internal ground levels should be created. This is done to avoid dampness on the floors of the building.
2. Partially Collapsed Foundation (or) Walls
Support the roof or the floor above using timber or steel columns. Accidental damage shall be avoided by providing additional supports.
Remove the damaged wall and stack the materials that can be reused later.
Rebuild the wall and make sure that it is tied to the rest of the walls in a toothed manner.
Remove the timber or steel supports only after the masonry has achieved the required strength.
If a large part of the foundation is damaged, then it has to be rebuilt in stages. If there are only cracks in the foundation walls, they may be filled or stitched using the recommendations given in section 1.3 on the repair of cracks.
If a large part of the foundation is damaged, then it has to be rebuilt in stages. If there are only cracks in the foundation walls, they may be filled or stitched using the recommendations given in section 7 on the repair of cracks.
3. Strengthening of the Corners
In many cases, the corners of buildings may get damaged due to flood waters - this can lead to the weakening of the walls. The worn-out corners of masonry walls can be strengthened by the following measures:
Remove the plaster and expose the cracked joints.
Remove all the loose particles with a wire brush and water.
After leaving a gap of 15 mm, fix the corner with a welded wire mesh of size 25X50 mm that is made of 8-gauge wire.
Cover the welded mesh with chicken wire.
Plaster the corner with a cement mortar of ratio 1:3 (1-part cement with 3 parts of sand).
The thickness of the plaster must be 38 mm (1.5 inches) so that there is enough to cover the welded mesh.
4. Temporary Care
Further, in the event of a collapsed wall or a damaged roof, the first step in the repair of a building affected by flooding is to temporarily support it using props. Planks can also be used to support an outward leaning wall. Ensure that the post used to support the roof or the wall is rested properly on a plank and that the load is transferred onto the ground.
5. Buttress Walls
Given the outward leaning of walls, buttress walls can be added on the outside to enhance their strength. The buttress walls must be properly integrated with the bulging wall.
6. Salt Crystallization on Walls
Plastering the walls using a rich cement mortar results in water rising to further heights. Hence, it is a wrong practice leading to the shift of damages from lower to upper portions. Many new buildings will have a damp-proof course in the form of a concrete belt, but it is absent in old buildings where the problem is severe. So, they may be damp at lower heights and as a result, there may be white deposits appearing on their surface.
The white deposits are the salts that come with the floodwater. The mechanical stresses that are created when the salt crystallizes might make the wall crumble. The salts on the wall can be removed using a simple technique.
Apply a layer of paper pulp (newspaper immersed in the water for a few hours, then crushed by hand) over the wall and leave it to dry.
As the paper pulp dries, the water evaporates and the salts that are left behind with the paper pulp can be removed later.
Continue this process a minimum of three times to completely remove the salts.
7. Repair of Cracks
In addition to salt crystallization, the force of the floodwater hitting the walls can cause cracks on the columns, walls, floors, etc. If left unnoticed, these cracks may develop, and allow water to seep through them. The extended presence of moisture within the surface of walls, and other elements can end up causing deteriorating the structure. Hence, they need to be repaired at the earliest, to ensure the safety of the people residing in the building.
7.1 Materials Used
Cement grout and commercially available crack fillers are generally used for the repair of cracks in flood affected buildings.
Sometimes, cement grout will have to be injected using a syringe. The crack fillers can be used to fill in the hairline cracks on the walls. The advantage of these materials is that they do not shrink while drying. Besides, shrinkage reducing additives are also added to prevent shrinking and cracking due to their high water content. These ethylene glycol derivatives are commonly available in waterproofing companies.
Other materials such as chicken wire mesh and galvanized iron (GI) weldmesh can also be used for stitching hairline cracks together. Epoxy, a well-known crack filler, which is made up of two components (resin and hardener) has to be mixed just before use. It is a very strong bonding material and can be used to a minimum or as a last resort.
7.2 Minor Hairline Cracks (Less than 1 mm wide)
The following steps shall be taken in the sealing of hairline cracks:
Form a ‘V’ groove along the crack.
Remove all the loose particles using a wire brush and water.
Fill in the voids using crack fillers that are available at the hardware stores.
7.3 Medium Cracks (1-5 mm wide)
The following steps should be taken in the sealing of medium cracks:
Form a ‘V’ groove along the crack.
Remove all the loose particles using a wire brush and water.
Insert small nipples to ensure that the cement grout has entered inside the voids, as shown in the figure.
Apply the cement grout after it is mixed with non-shrinkage chemicals.
Apply plaster over the grout.
Carry out curing for a minimum of 15 days.
7.4 Major Cracks (Above 5 mm wide)
The following steps shall be taken in the sealing of major cracks:
Form a “V” groove along the crack.
Remove all the loose particles using a wire brush and water.
Small stone chips can be inserted into the larger voids. Chicken wire mesh may also be fixed along the wall using nails. It should have a proper cover to avoid any corrosion in the future.
Non-shrinkage cement grout and mortar shall be used to fill in the smaller cracks.
Carry out curing for a minimum of 15 days
8. Cracks in Concrete Columns
Cracks in concrete columns can be stitched by inserting rods in the holes that are drilled in the concrete. After drilling, the holes can be filled using non-shrink slurry and epoxy.
8.1 Jacketing of Columns
The masonry columns may buckle or crack because of the sideways thrust exerted by the floodwater. In case, the foundation has weakened, the base of the column will have to be strengthened. The strength of the column can be improved by jacketing, which increases its size.
Jacketing is a technique for increasing the strength of existing structural components like beams and columns. It is carried out by wrapping them in a "Coat" of extra material. This additional material can be concrete, steel, FRP, etc.
9. Cracks in External Walls
If the foundation of the wall has undergone a differential settlement in the middle, the width of the crack in the wall will be wider at the bottom and narrower at the top. It will appear on both sides of the walls and will continue till the foundation. In extreme cases, the crack may appear on the floor of the corners of the building also. This happens more in the case of clayey soils and in places where the soil has been displaced by the floodwater. Depending on the width of the cracks, suitable remedial measures shall be taken as given in section 7.
If the foundation of the wall has undergone a differential settlement at the corners, the width of the crack in the wall will be narrower at the bottom and wider at the top. It will appear on both sides of the walls and will continue till the foundation. In extreme cases, the crack may appear on the floor of the corners of the building also. This happens more in the case of clayey soils and in places where the soil has been displaced by the floodwater. Depending on the width of the cracks, suitable remedial measures shall be taken as given in section 7.
If the foundation of the wall settles in one corner of the building, a diagonal crack as shown in the image develops. The width of the crack will be wider at the top and narrower at the bottom. It will appear on both sides of the walls. This happens in places when the soil near the corner of a building is displaced. This may not be visible in the foundation especially when it is constructed with stone and weak mortar. Depending on the width of the cracks, suitable remedial measures shall be taken as given in section 7.
10. Cracks Variable in Direction- External Walls & Internal Walls
Some buildings may have cracks ranging in size and direction; from hairline cracks to major ones. Floodwater may cause multiple damages to a building since many forces act at the same time. The foundation would have sunk, the walls would have got out of plumb and the roof would have weakened as well.
Proper reasoning of each of the cracks should be looked at and remedial measures should be taken accordingly. In many cases, the buildings will continue to develop cracks as the shrinking clayey soil becomes drier during the summer. It is very rare that the building needs to be demolished, and expert opinion is to be sought in such cases.
11. Cracks in Openings
Cracks may develop in arches after the floods. In most of these cases, the cracks may not be a threat, since the shape of the arch will re-adjust to take the load. The cracks may be filled with cement grout, after adding non-shrinking additives.
12. Summary
Climate change and global warming are very real threats. We have to face the reality of the rising sea levels and plan for the future. The quality of construction has to be improved for buildings to survive longer and to resist flooding. People should encourage good quality workmanship over the speed of completion. It is necessary for people to know about the construction and repair of buildings affected by floods. Simple methods as mentioned above can be used for the repair of cracks, but they should be done with professional help.
In the next article, we will explore the effect of flooding on concrete slabs, and how to repair them.
Check out the other two parts of this series of blogs on repairing flood affected buildings:
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