Cement 5 min read
OPC or PPC? Choosing cement for a Malnad build
Most houses here should be buying both. The mistake is using one bag type for the whole build because it was cheaper on the day.
Short answer
Use OPC 53 for structural RCC — columns, beams and slabs — where you need strength quickly and the formwork has to come off on schedule. Use PPC for plaster, masonry and mass concrete: it works more smoothly, generates less heat, and keeps gaining strength for months. Buying both for one house is normal and correct.
The difference in one sentence
OPC is ordinary Portland cement; PPC is the same clinker blended with fly ash. The fly ash slows the early strength gain and improves long-term durability, workability and heat behaviour.
Where OPC 53 earns its money
Structural RCC. A slab poured with OPC 53 reaches strength fast, which means the props and shuttering come off sooner and the next floor starts sooner. On a schedule-driven site that is worth real money. OPC 43 sits a step below and is fine for general concrete, flooring and masonry where speed is not critical.
Where PPC is the better buy
Plaster and masonry. PPC is noticeably smoother under the trowel, which matters when a mason is working a large wall. It also generates less heat as it sets — useful in mass pours and in hot weather, where an OPC mix can develop thermal cracks. And it keeps gaining strength well past 28 days.
The monsoon storage problem
This district is humid for months at a stretch. Cement absorbs moisture from the air, and a bag left on a bare floor against an outside wall will lump within weeks. Stack on planks, keep it off external walls, cover it, and use it within about three months of the bag date. Buying a full truck to save a few rupees per bag is a false economy if a quarter of it hardens before you use it.
Nominal mixes, and when to stop using them
M15 is 1:2:4, M20 is 1:1.5:3 and M25 is 1:1:2 by volume. Those are fine for footings, levelling and non-critical work. For anything structural, use the design mix your engineer specified — not the ratio the mason remembers.
