Construction Basics
Use of Various Concrete Grades During Building Construction
Updated: 4 November 2026
Choosing concrete for a home is not simply a matter of ordering the strongest mix. The concrete below a footing, the reinforced columns and the roof slab perform different jobs. The correct grade comes from the structural drawings and project specification—not a generic rule based only on the number of floors.
This guide explains the use of various concrete grades during building construction in Bangalore, from nonstructural PCC to reinforced concrete, and the checks homeowners should ask for before each pour.
What does M20 or M25 concrete mean?
The letter M denotes the mix, while the number denotes its characteristic compressive strength at 28 days, measured in N/mm² (equivalent to MPa), under standard testing. M20 means 20 MPa; M25 means 25 MPa. This is a strength class, not the total load a column can carry: member dimensions, reinforcement, loads and detailing also matter.
Concrete grade is also different from cement grade. A cement bag marked 43 or 53 does not mean that the finished concrete is automatically M43 or M53.
Concrete-grade comparison at a glance
| Grade | Characteristic strength at 28 days | Typical application—not a project specification |
|---|---|---|
| M10 | 10 MPa | Lean PCC or levelling beds where the specification permits |
| M15 | 15 MPa | Some plain-concrete bases, nonstructural works and pathways, subject to loading and exposure |
| M20 | 20 MPa | Minimum RCC grade for mild exposure under IS 456; use only where design and durability checks allow |
| M25 | 25 MPa | RCC where specified; minimum for moderate exposure under IS 456 |
| M30 | 30 MPa | Designed structural mixes where specified; minimum RCC grade for severe exposure |
| M35–M40 | 35–40 MPa | More demanding structural or durability requirements; exposure minima rise to M35 for very severe and M40 for extreme conditions |
These examples are not interchangeable. A foundation, slab or column may require a higher grade than the example because of load, soil conditions, span, exposure or the structural system.
1. Excavation and PCC below footings
Plain cement concrete (PCC) below a footing provides a clean working surface for setting out reinforcement and helps separate the structural pour from soil. M10 or M15 are common specification choices for some lean PCC works, but neither is a universal code requirement for every PCC application.
The structural engineer specifies the bed thickness, grade and extent. A levelling layer is not a substitute for a properly designed foundation, and weak soil cannot be solved simply by increasing the concrete grade.
2. Reinforced footings and foundations
The actual RCC footing transfers the building load to the ground. Its grade depends on the foundation design, soil investigation, loading, groundwater conditions and exposure. M20 or M25 may appear in residential drawings; higher grades may be required.
Before pouring, check the approved grade, reinforcement arrangement, concrete cover, excavation condition and the absence of standing water or loose soil. Do not confuse the low-grade PCC bed with the reinforced footing above it.
3. Plinth beams
Plinth beams tie structural elements together where provided by the design and may support wall loads. Use the grade shown on the structural drawing, often M20 or M25 in residential specifications where appropriate, rather than selecting it by habit.
Original site photograph from our JP Nagar plinth-beam preparation article. Reinforcement is visible; a photograph alone does not establish the concrete grade or test results.
4. Columns
Columns carry loads from the upper structure down to the foundations. Their grade is chosen with reinforcement, dimensions, slenderness and the full building loading in mind. M20, M25, M30 or higher may be specified depending on the design.
Do not assume that a single-storey house always needs M20 or that every extra floor means M25. Tell the engineer about intended future floors before design is finalised. Changing grades or adding floors later requires a structural review.
5. Beams and suspended slabs
Beams and slabs work together to carry floor loads. The approved grade depends on spans, loads, deflection requirements, exposure and detailing. M20 and M25 are familiar residential grades, but neither is a universal recommendation.
Confirm the pour sequence, construction-joint locations, reinforcement cover, embedded conduits and compaction arrangements. A planned construction joint may be acceptable when designed and executed correctly; it is not necessary to claim that every roof must always be poured in one uninterrupted operation.
Original photograph from our triplex-house bar-bending article, showing reinforcement preparation before concrete placement.
6. Staircases, lintels and chajjas
Reinforced staircases, lintels and projecting sunshades are structural elements—even when they look small. They must use the specified RCC grade, reinforcement and cover. Do not downgrade an RCC lintel or chajja to M15 merely because of its size.
Cantilevered elements need particular attention to reinforcement position, anchorage and curing. The correct concrete grade cannot compensate for misplaced steel.
7. Ground-floor bases, screeds and external paths
A nonstructural plain-concrete base may use M10 or M15 where the specification permits. A cement-sand screed is different from structural concrete, and not every floor layer is RCC.
Vehicle areas, industrial floors and heavily loaded ground slabs need their own design. Grade, slab thickness, joints, sub-base preparation and load requirements must be considered together; a domestic floor-base example should not be applied to a VDF or industrial floor.
8. Sumps, tanks and retaining walls
Water-retaining structures and retaining walls need specialist design for their loading and service conditions. Do not select M20 or M25 and assume a waterproofing additive will make the structure watertight.
Grade, water–cement ratio, crack control, reinforcement cover, joints, compaction and curing all matter. Water-retaining structures may require the applicable IS 3370 provisions alongside other relevant standards. Ask the engineer for the complete specification rather than relying on a generic grade chart.
Exposure can change the minimum RCC grade
IS 456 Table 5 sets durability-related minimum grades for reinforced concrete by exposure class:
| Exposure class | Minimum RCC grade |
|---|---|
| Mild | M20 |
| Moderate | M25 |
| Severe | M30 |
| Very severe | M35 |
| Extreme | M40 |
These are exposure minima, not automatic design approvals. The engineer also checks structural strength, maximum water–cement ratio, cement content, cover and any applicable special standards. Do not classify an entire Bangalore project as mild exposure without assessment; ground conditions and different parts of the building may require different treatment. Consult the current standard and applicable amendments.
Design mix versus nominal mix
A concrete grade is not a guaranteed cement:sand:aggregate ratio. IS 456 favours design mix concrete, with proportions developed for the actual materials, workability, strength and durability requirements. Nominal mixes are permitted only within the standard’s limits and conditions, generally for M20 or lower—not a blanket allowance for M25.
Avoid using a generic ratio such as 1:1.5:3 as proof that M20 has been achieved. Whether concrete is site-batched or supplied as ready-mix, controlled proportioning and the specified testing are essential. Ready-mix is a supply method, not evidence by itself that every pour meets its specification.
Quality checks that matter as much as grade
- Match the drawings: record the specified grade for each member before ordering or batching.
- Check the delivery or batching record: confirm the grade, approved mix and intended pour location.
- Control added water: do not add water casually to make concrete easier to place; follow the approved procedure and mix limits.
- Check workability: carry out the specified slump or other workability checks. Slump does not prove compressive strength.
- Place and compact properly: avoid segregation and ensure reinforcement and formwork are not displaced.
- Sample and test: take samples at the specified frequency and use the required acceptance criteria. A 7-day result can indicate progress; it does not replace the specified 28-day acceptance assessment.
- Plan curing: protect concrete from moisture loss and follow the engineer-approved method and duration for the cement type and weather. The 28-day strength age is not a universal instruction to stop or start curing on a particular day.
- Review defects: honeycombing, unexpected cracking or failed tests need engineering assessment, not cosmetic patching alone.
Frequently asked questions
Can I use M15 for a roof slab?
Not as a general specification for a reinforced roof slab. IS 456’s minimum for RCC in mild exposure is M20, with higher minima for harsher exposure. Follow the engineer’s drawing, which may require more.
Is M25 always better than M20?
It is a higher specified compressive-strength class, but suitability depends on the design and durability requirements. Unapproved changes can create coordination problems and do not fix poor compaction, curing or reinforcement detailing.
Does using 53-grade cement guarantee strong concrete?
No. The finished concrete grade depends on the approved mix, constituent materials, water control, placement, compaction and curing, verified through the required testing.
Can I identify the grade from a photograph?
No. Site photos document work, but grade and compliance must be established from specifications, batching or delivery records and test reports.
Plan the specification before construction begins
Ask for a member-by-member concrete schedule, the mix and testing requirements, and the curing plan before the first structural pour. This helps the homeowner, engineer and site team work from the same agreed specification.
For a Bangalore house-construction discussion, contact Kumud Innovator. You can also read our guide to government approvals before starting construction and curing methods that reduce repeated water application.
References and scope
- IS 456:2000 — accessible reference copy, especially Table 5 and mix-proportioning provisions. This older copy must be read with current applicable amendments.
- National Council for Cement and Building Materials — exposure and durability reference.
- Bureau of Indian Standards for current standards, amendments and applicable structural and water-retaining provisions.
This is homeowner education, not a structural design or a substitute for project-specific engineering advice. Typical grade examples must not override approved drawings or applicable standards.