How to prevent dampness in a building

How to prevent dampness in a building

Dampness in a building may occur due to faulty construction, the use of poor-quality building materials or bad architectural design. Dampness affects the lifespan of a building or structure, but it also creates unhygienic conditions. Mold and fungi love to grow in damp conditions, so it is best to fix any signs of wet concrete as soon as possible.

The measures taken to prevent water from leaking into a roof is usually called waterproofing. The treatment given to a structure to keep its basement, floor and walls dry is called damp proofing. Some of the problems caused by dampness in a building include the disintegration of bricks, stones, tiles; the softening and crumbling of plaster; the corrosion of metals; the warping, buckling and rotting of timber; the presence of termites; deterioration to electrical fittings and the bleaching and flaking of paint with the formation of coloured patches.

What causes dampness in a building?

The absorption of moisture by building materials is one of the main causes of dampness. This can be caused by faulty structure design, bad workmanship or the use of defective structures or materials.

Sources of dampness in buildings include the rising of moisture through the foundation walling; splashing rainwater which rebounds after hitting the wall surface; penetration of rainwater through unprotected tops of walls, parapets or compound walls; gutters which allow rainwater to descend through the top supporting wall. In the case of buildings with flat roofs, inadequate roof slopes, improper rainwater pipe connections and defective junctions between roof slabs and parapet walls can also cause dampness.

How to prevent dampness in a building

1. Membrane Damp Proofing

This involves placing layers of water-repellant materials between the source of dampness and the structure. This type of material is commonly known as damp proof course (DPC). It could be made from materials like plastic or polythene sheets, cement-based concrete, bituminous felts or asphalt. Applying DPC in a basement is usually referred to as tanking and can prevent ground moisture from seeping into the concrete walls.

2. Integral Damp Proofing

This form of damp proofing involves adding certain waterproofing compounds to the concrete mix to increase its impermeability (resistance to absorbing moisture). The compounds made from sand, clay or lime help to fill the voids in concrete and make it waterproof. Compounds such as aluminium sulfate, calcium chlorides and alkaline silicates chemically react when mixed with concrete, producing waterproof concrete.

3. Surface Treatment

This type of treatment involves filling up the pores of the surfaces subjected to dampness. Water repellent metallic soaps such as calcium and aluminium oleates and stearates are often used for this purpose. Cement coating, transparent coatings, paints, varnishes and bituminous solutions also fall under this category. Another economical option for damp surface treatment is lime cement plaster. This effectively prevents dampness in walls as a result of rain.

4. Guniting

For this type of damp-proofing, a cement gun machine is used to deposit a layer of rich cement mortar over the surface. The surface must be completely cleaned of dirt, dust, grease or loose particles by wetting it properly. Cement and sand (or fine aggregates) are then fed into the machine. This mixture is finally shot onto the prepared surface under a pressure of 2 to 3 kg per square centimetre by holding the nozzle of the cement gun at a distance of 75 to 90 cm from the working surface.

5. Cavity Wall Construction

This form of damp-proofing consists of protecting the main wall of a building by an outer wall, leaving a cavity between the two walls. The cavity prevents moisture from spreading from the outer to the inner wall.

These five methods of damp-proofing will help to protect concrete structures from excess moisture, which can lead to mold, fungus, rot and damage to buildings. Contractors and homeowners must always inspect their buildings for any signs of stress and damage, such as dampness, which could affect the integrity and durability of the structure.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

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LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

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At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

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How to waterproof concrete structures

How to waterproof concrete structures

Waterproofing concrete structures can help to protect them from the weather and keep them in optimal condition. This is especially important in areas prone to flooding, heavy rainfall and constant ocean vapour. Water can penetrate concrete over time and affect its strength, so waterproofing is a good way to keep a building strong.

There are numerous ways to waterproof a concrete structure. Contractors can apply paints and bitumen felts to the exterior of the building, or they can use concrete admixtures to prevent water from penetrating the surface of the structure. For optimal waterproofing results, the design, workmanship and building materials should conform to the correct standards and codes of construction.

Concrete waterproofing admixtures

Certain admixtures make concrete impermeable to water and moisture. These chemicals can be added to the concrete or plaster batch during mixing. They reduce water permeability in the concrete by reducing the size and number of pores in the surface. They also line the surface with hydrophobic materials that prevent the absorption of water.

These admixtures react with the calcium hydroxide in the cement to create a hydrophobic layer. Examples of waterproofing admixtures include animal fats, stearic acid and some vegetable oils. These admixtures can also be mixed with plaster to line the surface of a wall. This acts like a layer of waterproof paint that repels rain, standing water and mist in the air.

Waterproofing concrete with bitumen coating

Another way to make concrete structures waterproof is to place a layer of bitumen on the exterior surface. The concrete first needs to be cleaned and sanded to give the bitumen a rough surface to stick to. Contractors should pour hot bitumen (about 1.5kg per square metre of concrete) onto the surface and spread it evenly. 

Once the first coat had dried and cooled, the second coating (1.25kg per square metre) is applied in the same manner. Immediately after the application of the second coating, contractors should spread sand over the surface. This is then left to dry and cool. The sand will give the surface a non-slip texture and improve the durability of the bitumen.

Certain concrete structures need to be waterproofed internally, such as concrete tanks and reservoirs that will store certain chemicals and liquids. Waterproofing a concrete structure will maintain its strength in the face of exposure to water and other liquids. It will prevent concrete rot and protect a building from heavy rains, flooding and salt moisture from the ocean.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

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Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.

Moisture changes can affect concrete

Moisture changes can affect concrete

Moisture changes or the incorrect water content can affect concrete. It often leads to small cracks that are caused by the shrinkage of the concrete as it dries out. Concrete is slightly porous – meaning that it can absorb and lose water fairly easily, even moisture from the air. This results in the expansion and contraction of the concrete, depending on the moisture changes.

Concrete is most affected by moisture changes in its early stages of setting and curing. That is why it is so important to keep concrete damp for the first few days while it cures. During this phase, the concrete can undergo irreversible changes if it is left to dry out completely, such as cracking under shrinkage.

Types of cracks in concrete resulting from moisture changes

1. Initial shrinkage cracks in concrete

Initial shrinkage causes small cracks when there is not enough moisture during the setting process (the first 12 hours after pouring). These cracks are partly irreversible and they occur in all cement-based building materials, such as concrete, mortar and plaster. This initial shrinkage is one of the leading causes of hairline cracks in concrete structures, but it can be avoided.

Firstly, contractors need to make sure that they are using the right cement-to-water-to-aggregate ratio. Follow the instructions on the cement bag for the optimal ratios to use. This will ensure that there is enough water to prevent the fresh concrete from drying out and cracking. Proper curing for the first seven days after pouring can also prevent initial shrinkage cracks.

2. Plastics shrinkage cracks

Cracks that appear on the surface of concrete during the curing phase are a sign of plastic shrinkage. A few factors can cause plastic shrinkage, including rapid evaporation of surface water. This causes water on the surface of the structure to dry out, which then creates cracks in the surface layer of the concrete.

Plastic shrinkage is more likely to occur in hot and dry climates when the water on the surface of the concrete evaporates rapidly. Contractors need to keep the surface of concrete wet during the first seven days on concrete curing. This is the best way to prevent the concrete from drying out and, therefore, plastic shrinkage.

3. Plastic settlement cracks

Plastics settlement cracks are similar to plastic shrinkage cracks. They are caused by the settlement and separation of heavy aggregates in the concrete mix. As these aggregates sink to the bottom of the mix, it leaves a concentrated cement and water mix near the surface of the structure, which then cracks. Some reinforced concrete suffers from plastic settlement cracks too. As the aggregates sink, they hit the steel reinforcing but it forms small voids above the aggregate particles. These voids can then create cracks in the structure.

These causes of cracking on concrete structures are all linked to moisture changes. That is why it is so important for contractors to use the right amount of water in their concrete mix and to keep the structure damp during the initial setting and curing phases. Moisture changes are an important aspect of construction, but knowing what to look for can help contractors prevent their structures from cracking.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.

What causes concrete sweating?

What causes concrete sweating

Concrete sweating is the name given to the appearance of water drops on the surface of concrete. These wet patches on a concrete floor or wall make it look as if the concrete is sweating. The problem occurs when there is a big difference between the internal and external temperatures of the concrete.

A number of co-occurring factors often need to be present for concrete sweating to take place. There are also a few other causes that can create wet patches on a concrete surface, all of which are outlined below.

Causes of concrete sweating

1. Dew Point

Dew point in the atmosphere is the most common cause of concrete sweating. In countries like Tanzania, concrete sweating can happen when warm and humid air hits cold concrete inside a building. The moisture in the air cools and condenses on the surface of the cold concrete, making it wet and slippery. However, the concrete needs to be below the dew point temperature for concrete sweating to occur.

2. Wet adjacent soil

Concrete sweating can occur in retaining walls and basements where the soil on the other side of the wall is wet. Although concrete is a solid material, water and moisture can seep through it. Water from the soil can slowly creep through the concrete wall and appear as concrete sweating on the other side.

3. Salt deposits

Salt deposits in concrete can attract moisture from the air. Sometimes there are natural salts in the aggregates that are used to make the concrete, or salt occurs from a process of salt finishing a concrete floor. Either way, salt absorbs moisture from the air and leads to concrete sweating on the surface.

4. Cleanliness of concrete

The cleanliness of a concrete floor or slab can cause it to sweat. Dirt can reduce the permeability of the surface, which means that water vapour sits on the surface instead of being absorbed into the concrete. This often happens on factory floors where rubber from forklifts and trolleys is deposited on the surface.

How to fix and prevent concrete sweating

There are a number of ways in which concrete sweating can be prevented and cured. Firstly, good maintenance and cleaning practices can prevent any salts and dirt from excess moisture on concrete surfaces. We have some good cleaning tips to guide you.

Sweating can also be prevented by opening windows and doors to allow air to flow through the building. If the air movement inside a room is not sufficient, then the humidity can increase and the moisture has more time to seep into the walls and floors. Another way to stimulate air flow is to switch on ceiling fans in hot and humid conditions.

___

LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.

The importance of concrete curing

Workers pouring and curing concrete

Concrete curing is the process of keeping freshly-poured concrete from drying too quickly. It determines the final strength and quality of the construction.

Concrete actually needs moisture to set, especially when a hydraulic cement is used in the mix. The right moisture conditions, temperature and time are essential for a strong concrete – it enables the concrete to gain more strength over time.

The curing time is dependent on the concrete mix – too watery and the concrete will take too long to set; too dry and the concrete will set prematurely, shrink and become brittle. Time is needed for strong bonds to form between the cement and aggregates.

As concrete dries, moisture rises to the surface. If this moisture evaporates too quickly, the concrete can shrink and crack. If it doesn’t cure properly, concrete can develop weak qualities similar to chalk – it can crumble and become dusty. Here’s how to ensure you cure concrete properly to create a strong and durable structure.

How to cure concrete properly

There are numerous ways to cure concrete correctly. Regardless of the method you choose, it is important to leave the concrete forms in place long enough to keep the moisture in and prevent it from drying too quickly.

  • Water curing – This method involves flooding or misting the surface of the concrete with water. It’s common to see construction workers hosing down concrete. Water curing is an easy and effective method that keeps vital moisture in the concrete until strong bonds are formed.
  • Water retaining – This method uses damp coverings such as river sand, straw, canvas or woven sacks. These materials are kept wet during the curing process and are better suited in extreme temperature environments; in hot climates, the damp covering is less susceptible to evaporation than surface water; in cold climates, the covering prevents water from freezing and cracking the concrete.
  • Waterproofing – This method uses waterproof plastic or paper on the surface of the semi-dry concrete. Once the concrete is hard enough to resist surface damage, a plastic covering can be applied to keep remaining moisture in. This method can cause discolouration of the concrete, so it should not be used if the appearance of the concrete is important.
  • Curing chemicals – This method entails adding chemicals to the concrete as soon as it has been poured. Curing chemicals, such as oils or soluble waxy emulsions, can be sprayed onto the surface of concrete and left for a few weeks. They will naturally break down when exposed to sunlight, and some chemicals can make the concrete slippery, so avoid using on surfaces where grip is important.

How long does the curing process take?

Ideally, a concrete slab should be kept moist and warm for the first month after pouring. The first week is the most important, so if deadlines are approaching and time is short, keep the concrete moist and between the temperatures of 10 and 32 degrees Celcius for the first seven days.

Concrete only reaches its full strength after 28 days. The longer you allow it to cure under the correct moisture and temperature conditions, the stronger it will become. This strength, often called concrete cylinder strength, is important for large buildings and surfaces that will be put under a lot of weight, such as industrial floors and foundations.

The difference between concrete curing and setting

Concrete is set when it is hard enough to support some weight without being damaged – typically after three days. This means you can walk on it without leaving footprints. Concrete is cured when it has reached its full strength and can support all the weight that it was designed for – typically after 28 days.

Depending on environmental conditions, concrete can set and cure in different amounts of time. Like curing, the setting time is dependent on the concrete mix and external environmental factors such as temperature and moisture.

In some hot climates, concrete can set within two hours of being poured but in cold climates, it can take a number of days. If temperatures are below freezing, concrete may not set at all. The curing time follows the same logic.

Using the right concrete mix in the right environmental conditions is important for a strong structure. The curing time directly determines the strength of concrete, so be sure to allow the concrete to cure properly before placing heavy loads on the surface.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo brand for over 30 years. Our head office and fully-integrated plant are located in the Mbeya Region in Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy DIY projects and the latest industry news. See our Instagram channel for more insights into our work with local communities.