Waterproofing Systems for Concrete Basements

Preambles

Waterproofing Systems for below ground structures are faced with more stringent requirements regarding durability, exposure and stress conditions, construction method and sequence, ease of application and total cost management. In addition, sustainable system solutions are becoming more important in order to save natural resources, energy and water, plus CO₂ etc.

Basement or any below-ground structure, that is formed by a base slab/raft, walls and a top/grade slab, is partially of fully exposed to the surrounding soil and groundwater, resulting in specific exposure and stress from the prevailing permanent or temporary environmental conditions.

Of late, most of the buildings designed for a service life of 50 years or more. Hence, needless to mention, any lack of water-tightness severely reduces the long-term durability of a building or other below-ground structure and badly affects its planned use as water ingress will result in physical attack and deterioration of the concrete. This leads to expensive structural repair works, damage or loss of interior finishes and goods, operational downtime, or serious impact on the internal environment from damp and condensation.   

The selection of the appropriate waterproofing methods, the project specific design of the chosen waterproofing system and its correct execution on site are key elements in minimizing the Total Cost of Ownership. A waterproofing system typically amounts to less than 1% of the total core construction cost, yet the selection of a high-quality waterproofing solution can easily save this amount or more, in future maintenance and repair costs over the service life of the structure.

Understanding Projectized Exposure and Stress

Owner’s Project Requirements

To define the appropriate waterproofing strategy and type of system for a specific project, it is important to consider not only the ground condition but also the project requirements of the owner: Functionality and future use, the service life and the total cost of ownership.

Basement Water proofing – Concept and Strategy

In general, there are 3 different waterproofing concepts which can take all of the relevant project requirements into consideration.

Waterproofing Technologies

Now-a-days, most of the waterproofing systems provides full range of technologies and systems used for below ground waterproofing. This includes highly flexible membrane systems, liquid applied polymeric membranes, water tight concrete admixtures, joint waterproofing systems, waterproofing mortars and coatings, as well as injection sealing grouts. All these solutions are designed to be used together to meet the specific needs and requirements of owners, architects, engineers and contractors on site.

The performance of each different waterproofing technology can generally be positioned as follows,-

Selection Criteria

Selection of appropriate type of water proofing treatment for your project basement is an imperative task and shall be done very meticulously.

Now-a-days there are at least more than a dozen of water proofing treatments available for basement water proofing. Out of those, based on your project requirement, specific type to be finalized.

Selection of suitable type of water proofing largely depends upon the existing ground water table (during summer & monsoon) of the project premises.

In general, if the existing underground water table during monsoon is considerably below than the basement raft bottom, single or double component modified (or pure) polymer-based water proofing treatment is recommended. Where water table is higher, HDPE membrane type treatment is recommended.

Schedule the Pour Plan

Post to that, concrete pour plan (for basement raft & wall) to be finalised for sequential resources management.  

To know ‘Where to put construction joints and how?’ please refer the respective blog in detail.

Which side?  Positive/Negative?

For water proofing treatment, it’s always advisable to do from positive (external/outside of basement raft & wall) side.

In case, basement &/or retaining wall concreting is already done and the outer space is inaccessible, there is no option but to do the treatment from negative side, which is not preferable. 

Sequence of works

Water proofing of basement raft shall be done over the blinding/lean concrete/levelling course (i.e. PCC), before basement raft concrete. Whereas on retaining wall it will be done post concreting.

Depending upon the type of treatment, it is recommended to have a protective plaster (1:5) of 10-12mm shall be done over horizontal/vertical coated area/surface, admixed with integral waterproofing compound as per manufacturer specification.

RCC of Basement Raft & Retaining Wall

Considering the site constrains, RCC of raft & retaining wall shall be done as per feasible pour plan. The concrete (M-30 grade/as recommended) shall be provided with PC based superplasticizer and Fiber (of 12mm length) or equivalent, as per manufacturer’. Water swell bar/PVC water stopper of appropriate size shall be provided. Construction joint treatment with high strength repair mortar.

Other Good Practices

It’s always better to Please ensure no expansion joints designed/left in basement raft & retaining wall.

1. Pour Plans with alignment of proposed construction joints shall be done as per approved codal guidelines. (For details, please refer our blog on the subject topic).

2. Prior to execution, the same shall be vetted by the concerned consultants and approve for execution.    

3. Proposed and approved construction joints surfaces shall be terminated with appropriate formwork with shear keys/factory manufactured metallic construction joint sheets.  

4. Use of Water swell bar/PVC water stopper of appropriate size shall be provided in every horizontal & vertical construction joint of basement raft and wall.

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5. In the construction of basement, tanks and swimming pool etc., the construction joint between the walls and the base is facilitated with the use of kickers/starters, which are best cast monolithically with the base slab. In this case, kickers should be at least 150mm height, and should incorporate the water bars.

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6. In case, the above-mentioned monolithic kicker not constructed with water bars, risk of water penetration increases. However, in that case, hydrophilic (water swellable) water bars can be used as next alternative.

7. Prior placing of new concrete, existing concrete surfaces shall be hacked, cleaned and treated carefully.

Depending upon the ‘age’ of the existing concrete, general modality and specification furnished below for ready reference,-

If within 12 hours (green concrete):

• Key joints/shear key,

• Remove the laitance/loose concrete.

Within 12 hours to 3 days

• Key joints/shear key,

• Remove the laitance/loose concrete,

• Use cement slurry @ 24Kg/SqM or latex-based bonding agent to be applied.

Within 3 days to 7 days

• Key joints/shear key,

• Remove the laitance/loose concrete,

• Use Epoxy/Resin (polymer based) bonding agent to be applied as per manufacturer’s recommendation.

If the joint is more than 7 days

• Better to use shear connector,

Or

• Use Epoxy based bonding agent to be applied as per manufacturer’s recommendation.

Please note, Latex/Epoxy based bonding agent shall be used within 30min prior concreting.

But, with advancement of (nano) technology, high performance reactive & flexible bonding agents are available for concrete (cold) joints which can be used 30min to 72 hours, prior concreting. 

8. For retaining walls, use of ‘center-pins’, in place of conventional through-and-through form work tie-rods, are recommended. 

Prior procurement, it’s advisable to check the adaptability of the center pin with formwork tie rods and its pull-out strength. For each ply boards (1.22m x 2.44m size) 9 nos. required. Approx. Cost @ Rs 140/piece.    

9. All PVC tie-rod sleeves shall be removed (by using appropriate dia drilling bit), prior plugging the holes with pressure grout, using appropriate chemicals (where water table is higher) or equivalent.

Waterproofing for Retaining wall (external surface)

Where ground water table is considerably below the basement raft, the external surface of the retaining wall shall be painted with two coats polymer modified cementations paint sand sprinkled on the coating to take the plaster course.

Tie rod hole treatment & construction joint treatment with high strength repair mortar as per manufacturer’s specification.

Protective plaster (1:5) of 20mm shall be done over horizontal coated area surface, admixed with integral waterproofing compounds, as per manufacturer specification. The plaster shall be finished with heat cement punning (also with integral water proofing compound) of 1.5mm thick.

Quality Workmanship and Assurance

This specialised job shall be executed with experienced competent contractors with regular technical checks and supervisions.

A quality assurance certificate with a ten-year guarantee on stamp paper as per the approved format shall be provided by the applicator as well as the company whose chemicals are being used. (For sample format, interested reader may contact the author).

Indicative Cost Impact

Indicative cost of modified polymer based (single/double) compound waterproofing works (with all materials, labours, tools & tackles, scaffoldings etc. complete) may be considered as,-

For Basement Raft

• Treated over PCC with two coats of modified polymer based (single/double) compound @ Rs 400-450/Sqmt.
• Protective plaster (1:5, 10-15mm thk.) over horizontal surface, admixed with integral water proofing compound 400-450/Sqmt.
• Injection cement grouting with GI nozzle of 15mm dia, admixed with appropriate chemicals @ Rs 250-300/No.
• PVC water stopper bar/Hydrophilic swell bar @ Rs 1200 – 1500/Rmt.   

For Basement Retaining Wall (outside)

• Treated over PCC with two coats of modified polymer based (single/double) compound (sand sprinkled on the coating to take the plaster course) @ Rs 800-850/Sqmt.
• Protective plaster (1:5, 20mm thk.) over vertical surface, admixed with integral water proofing compound 450-500/Sqmt.
• Neat cement punning (1.5mm thk.), all over wall area @ Rs 120-140/Sqmt.
• Injection cement grouting with GI nozzle of 15mm dia, admixed with appropriate chemicals @ Rs 250-300/No.
• PVC water stopper bar/Hydrophilic swell bar @ Rs 1200 – 1500/Rmt.   

For Projectized Consultation

For personalized/projectized full-proof solutions with specific construction waterproofing chemicals, please contact Smart EngineerZ.

e-Mail : Smartengineerz4u@gmail.com; WhatsApp : +91-62913-24235  

Compiled & Written by: Avijit Datta [9874697360]

Disclaimer: All indicative images and few other references taken from internet and websites.