Ordering the wrong concrete mix for your slab can ruin the whole job. Too weak, and you’ll get cracking or deflection. Too dry, and it won’t level or bond properly. This guide walks through how to choose the right mix, calculate the volume, and make sure the delivery turns up on time and pour-ready — no guesswork, no overspend, no last-minute chaos.
First, identify what the slab is supporting. For domestic floors or extensions, C25 is usually fine. Garages or driveways may need C30 or higher. If there’s an engineer’s spec — follow it. For unreinforced slabs or exposed outdoor areas, you may need additives like waterproofing or plasticisers. If it’s polished concrete, you'll want a cleaner mix with fewer large aggregates. Always check what finish or load the slab will need to handle long-term.
Use a volume calculator or multiply: Length × Width × Depth (in metres) to get m³. For example, a 4m x 5m slab at 0.1m depth = 2.0m³. Always add 5–10% extra for spillage, waste, and edge correction — especially if your sub-base isn’t perfectly flat. If you're not confident in your measurements, speak to the supplier — most will help cross-check based on your slab size and depth.
Most slabs under 10–12m³ are best served by ready-mix delivery (from a mixer truck). For tight access, a barrow mix supplier may wheel it in on site. If you’re mixing on-site, you'll need exact cement ratios and a solid mixing plan. Ready-mix is the cleanest, most reliable option — and ensures consistency throughout the pour. Let the supplier know if it’s being pumped or wheelbarrowed to the site.
When calling a concrete supplier, tell them your slab type and load. They’ll usually recommend a C-code (like C25/30), slump range (how wet the mix is), and additives. Ask if fibre can be added for extra surface crack control. Confirm whether they’re batching on site (volumetric) or delivering pre-mixed. Also check how long the truck can stay before charges kick in (typically 30–45 mins unloading).
Let the supplier know about site access — is it pump access only, or can they back right up? Is the ground level or sloped? Will you be wheelbarrowing, raking from chute, or using a boom pump? Clear a space for the truck and plan your pour route. If pumping, book the pump in advance and confirm it’s suitable for slab mix. Ready mix waits for no one — so prep everything in advance.
When the truck arrives, check the delivery ticket for mix type, slump, and volume. Make sure it matches what you ordered. If it’s too wet or too dry, tell the driver immediately — they may be able to adjust it on-site (especially with volumetric trucks). Once you pour it, it’s yours — so confirm everything before it hits the slab. Keep the ticket for your records in case there’s any finish or strength issues later.
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