How do you waterproof a concrete water tank

Getting your concrete underground water tank waterproofed is wise rather than doing a layman job and suffering.

The concrete underground tank may develop a structural crack and lead to leakages both from outside and inside of the tank.

The development of structural Cracks may be due to different reasons

• Insufficient design of the RCC (Reinforced Cement Concrete) tank. Cracks develop due to the external pressure developed by the earth around the underground tank or groundwater pressure, especially during the rainy season.
• Once a crack is developed, underground water percolates into the tank along with soluble salts and cause further damage to the RCC structure – both the reinforcement steel and the concrete.

As the design of the RCC underground water tank is important for the success and durability, the waterproofing of the tank is also very necessary.

The waterproofing helps to negate the effect of negative water pressure and positive water pressure.

Negative water pressure is created by the groundwater on the external surface of the tank.

Positive water pressure is created by the stored water on the internal surface of the tank.

If we consider the financial implications and the ease of maintenance waterproofing becomes all the more important. Because the cost of repairing an underground water tank is far more than the cost of waterproofing during the construction stage itself.

Waterproofing both inside and outside the concrete underground tank surfaces

Here, I will give you the step by step waterproofing solution for your concrete underground water tank.

Note: The solution holds good provided the concrete structure is designed properly.

1. The concrete tank should be cured with water for 28 days after de-shuttering.

1. The surface of the tank should be cleaned of dust and free particulate matter and any loose concrete material with a water jet.
2. If any crack or honeycomb are observed on the concrete surface those should be filled with repair mortar. (The mortar may be Cement: Sand = 1:1 with the addition of non-shrink expansive chemical).
3. Check the volume of the tank should be greater than 4 times the surface of waterproofing.
4.  The inner surface should be damp with water but surface dry.
5.  Apply the waterproof paste in 2 coats. The 1st coat should be applied in a single direction – top to bottom or left to right. The 2nd coat should be applied perpendicular to the 1st coat.
6. Similarly, The outer surface should be damp with water but surface dry.
7. Apply the waterproof paste in 2 coats. The 1st coat should be applied in a single direction – top to bottom or left to right. The 2nd coat should be applied perpendicular to the 1st coat.

The waterproof chemical to be used may be in the powder form or in the liquid form depending on the manufacturer.

Different manufacturers have different products with respective brand names.

For this type of surface application for both positive and negative waterproofing, I will suggest

weberdry tex from Saint Gobain

This is a pre-mixed cementitious waterproof for underground concrete water tanks

The product is available in pack sizes of 5Kg and 20 Kg

When you buy to make sure the pack is not more than 1 year from the date of manufacture.

The paste is to be prepared by mixing weberdry tex: water = 3:1 with a slow speed mixer till consistency and lump-free.

2 coats are to be applied with each coat of 1 mm.

The product provides coverage of 5 Sqm/ 20 Kg bag.

Pros 

• Provide resistance to hard water and chlorinated water.
• Ease of application with a brush or trowel.
• Most suitable for water reservoirs.
• It is effective till 50m of depth.
• Resist water pressure both from inside and outside.
• Lower in VOC.
• Non-Toxic.

Cons

• Not suitable for application on porous surface, brickwork, light-weight concrete.
• Cannot be applied to structures subjected to movements or cracked structures.
• Not suitable for structures exposed to the acidic environment.
• The product is not flexible and tends to crack if there is structural movement.

Hope this gives you a fair idea of How to waterproof a concrete water tank with surface treatment.

Please put your comments if you have already used this technique and having a leakage-free tank.

If you have any success story using some other method please share in comments.

If you are facing any similar problem and do not know what is to be done, post the problem in the comments.

How to get a Waterproof Underground Concrete Water Tank

In every building be it residential, office, institute, hospital and so on we need to construct an underground concrete tank as a water reservoir.

Many times it happens that within a short period of time you face the problem of a leaking underground concrete water tank.

The problem of leakage may arise in a newly constructed water tank or an old water tank.

As you know prevention is better than cure. Hence, you must ensure to make the underground water tank waterproof during construction itself so that there is least possibility of the tank to leak after construction and also after many years of usage.

Waterproofing not only makes the water tank leakage-free but also gives strength to the structure.

Here are a few points that you must take care of during the construction phase

• The RCC water tank must be designed by a competent engineer - Reinforcements and Grade of concrete.
• Concrete mixing at site should be as per quality standards and as per the design mix. Weigh batching, Volume batching with concrete mixer is helpful.
• Line, level & dimension of each member of the tank should be maintained as per design.
• Placement of concrete with proper vibration techniques to release entrapped air and voids.
• Prevention of concrete-slurry loss during pouring and vibration with the use of cotton or foam plugs.
• Curing of the concrete structure after 24 hours for at least 7 days & up to 28 days. This is very important.

In addition to the above points, certain chemicals which have been developed as waterproofing chemicals are used at different stages of construction depending on the product to either make the concrete watertight and durable or to give a waterproof film layer blanketing the water retaining surfaces.

The theory states that concrete is watertight and truly so. This can be proved in a laboratory environment.

But all Civil engineers who are working in the construction field know the challenges they face while working at the site. 

The concreting conditions are most of the time not ideal and engineers need to meet the timelines.

Waterproofing is one field where much research has happened and many good products have been launched by various companies. 

What these chemicals do is help make the concrete impervious to water.

What will happen if Waterproofing is not done?

You will not face much problem in the structure in the first one year if there has been even an average quality of construction i.e. the construction been left to non-qualified supervisors and workers alone.

After the first year problems become visible. The root cause of most common problems is found out to be leakages, seepages, bulging and cracking of the concrete, plasters, pealing off the paints and dampness in the walls, formation of salty deposits.

Note that these problems might not appear in the whole of the structure. These are only at very small areas. 

Even these small problem areas will take away the peace of your mind and make you unhappy about your hard-earned investments. 

These problems do not stay at that, they grow in size very fast and exponentially. 

Many Technologies have been introduced by different companies in addressing the leakage problems in underground water tanks faced by engineers and owners in the country over the years.

You may ask, Will waterproofing not add to the cost of construction? Yes, waterproofing is costly. But it is worth the money spent. 

Believe me, I have seen from experience that the expenditure is worth having and will save much more in the long run. More importantly, it will buy you peace of mind.

For basic principles of concreting read waterproof underground concrete water tank 

Apart from adopting good practices during construction, we need to take care of the following

• The construction joints must be leak-proof.
• Treat the construction joints or cold joints using special methods.
• After construction and before usage, test the concrete tank by filling it with water and monitoring the water level inside, to identify any leakages.
• Pressure grout with 1:1 (Water: Cement) grout with the addition of waterproofing chemicals with the help of a manual pump if leakages are found at some points.

Use of waterproofing chemicals in concrete during construction 

Waterproofing chemical comes in liquid or powder form in different pack sizes.

For example, Dr Fixit Pidiproof LW+ from Pidilite Industries Ltd comes as a liquid in pack sizes of – 200ml, 1Ltr, 5Ltr, 10 Ltr, 20Ltr, 50 Ltr.

• The chemical is to be mixed with the concrete.
• The dosage of chemical is 200ml for 1 Bag (50Kg) of cement.
• The total concrete (Volume in Cum) to be used in the water tank can be easily calculated. You can follow my article on How to calculate the quantity of concrete in any structure. And the mix design will give the Bags of Cement / Cum of concrete. Read through the article on How to find cement bags quantity from mix design.
• Total chemical required will be 200ml x Total No. of Cement Bags
• Cost of 1 Ltr is about INR 155/-

Apart from waterproofing property, the chemical has some other benefits like

• Improvement in workability of concrete.

• Surface Cracking of Concrete is prevented.

• It protects the concrete from corrosion.

The chemical is easily available in the market. You may locate a dealer here (https://www.drfixit.co.in/locate/find-dealer)

Similarly, there are other chemicals too by Companies like Fosroc, Sika etc. 

I will bring you with similar other options with the comparative advantages and disadvantages.

Please let know how you look at this solution to waterproofing of underground concrete water tank. 

Write about your experiences and how you came out with an innovative idea. Let know what problems you are facing. 

We may find a solution together that will be helpful for all.