Not all concrete is created equal. If you want a slab that cures properly, resists cracking, and holds its strength long-term, additives make a big difference. From plasticisers and fibres to waterproofers and curing agents, these products help level up your mix — especially in challenging conditions or for high-performance builds. Whether you’re laying a garden slab or pouring a heavy-duty driveway, these are the top 10 concrete additives and admixtures that can improve durability, workability, and curing.
Plasticisers improve workability without adding more water to the mix. This means your concrete stays easy to pour and finish, but without sacrificing strength. Adding water to a dry mix can weaken it — but a plasticiser lets you maintain a low water-to-cement ratio for maximum durability. Ideal for DIYers using site mix, or for slabs where a smooth finish is important. Liquid plasticisers are added during mixing (usually in small doses, 100–200ml per bag of cement). They also help reduce shrinkage cracking and make your slab easier to compact properly.
Fibre additives are mixed into the concrete to reduce cracking, control shrinkage, and boost overall durability. They come in polypropylene (plastic), steel, or even glass fibre options. Fibres are especially useful for driveways, garden bases, and thin slabs where shrinkage and micro-cracking are common. They act as mini-rebar throughout the mix, binding the concrete internally and holding everything together as it cures. You’ll typically add 1–2 handfuls per 25kg bag of cement, or follow the manufacturer's weight ratio. It’s an easy, cost-effective way to make your slab stronger from the inside out.
Accelerators speed up the setting time of concrete, making them ideal for cold weather pours or when you need quick strength gain. This is especially helpful during winter or when pouring slabs that will need to be walked or worked on within hours. Most accelerators are added in liquid form and reduce the time it takes for the concrete to firm up and start curing. Be careful not to overuse them — too much can lead to shrinkage cracks or surface burn. For slabs, driveways, or footings, they’re a great way to keep timelines tight without compromising strength.
Retarders do the opposite of accelerators — they slow down the setting process. This is useful for hot weather, large pours, or intricate finishing jobs where you need more working time. Retarders help prevent cold joints in slabs that are poured in stages and reduce the risk of surface drying before finishing is complete. They’re especially handy if you're mixing by hand or pouring multiple sections. Most are liquid-based and added directly to the water or mix. They won’t reduce strength — they just give you more time to get the slab levelled and floated before it begins to stiffen.
Waterproofing additives help seal concrete from within by blocking capillaries that water uses to travel through the slab. These are perfect for slabs exposed to wet conditions — like driveways, garden bases, or garage floors. Unlike surface sealers, these additives work inside the mix and provide long-term protection against moisture ingress. They also help reduce efflorescence (white salts) and improve freeze-thaw durability. Often supplied as a powder or liquid, waterproofers are added during mixing and don’t affect workability much. Use them when drainage is poor or where you want extra protection from damp and water damage over time.
Air-entraining additives introduce tiny, evenly distributed air bubbles into the concrete. This boosts durability in freeze-thaw conditions by giving expanding water room to move without cracking the slab. They're commonly used in exposed or external slabs like driveways and garden bases. These micro air pockets also improve workability and reduce bleeding (excess water rising to the surface). Air entrainers are essential in colder climates and for slabs poured in winter. Most are liquid and added in small amounts — too much can reduce strength, so always measure carefully. A great option for weatherproofing your base against long-term environmental stress.
Proper curing is essential for concrete strength, and curing compounds help retain moisture in the slab during its early stages. These are sprayed on after the surface is finished and form a thin film that slows down evaporation. Curing compounds are especially useful on hot or windy days where water loss can lead to surface cracks and weak top layers. They reduce the need for constant hosing or wet coverings. Choose a water-based, clear curing agent for general slabs, or go for wax/resin types for driveways. A small investment that dramatically improves long-term concrete strength and durability.
Concrete naturally shrinks as it cures — and that shrinkage often leads to hairline cracks or surface separation. Shrinkage-reducing additives (SRAs) help minimise this by modifying how water evaporates and how the cement hydrates. These additives are ideal for slabs where visible cracking is a concern — like polished floors, driveways, or decorative concrete. They don’t eliminate the need for control joints, but they do reduce stress inside the mix. You’ll usually find them in liquid form, and a little goes a long way. Combine with fibres or mesh for maximum crack control across larger slab pours.
Using supplementary cementitious materials like GGBS (ground granulated blast-furnace slag) or PFA (pulverised fuel ash) can improve long-term strength, lower heat during curing, and enhance chemical resistance. These materials are blended with standard cement and are often found in premixed “eco” or industrial-grade bags. They slow down early curing slightly but improve long-term durability — especially for large pours, hot weather, or chemically exposed slabs. Builders use these for more sustainable mixes and for slabs that need to hold up against aggressive conditions. A professional-level tweak that offers big performance benefits over time.
If you’re pouring a new slab over existing concrete or bonding a screed to a base, a bonding agent is essential. These additives help the new layer adhere properly to the old surface. Without them, the layers can separate or delaminate — especially under load. Bonding agents are applied as a slurry mix or primer coat before the new concrete goes down. They create a chemical and mechanical bond that locks both layers together. For overlays, repairs, or layered slabs, this additive turns your mix into a unified structure. It’s a small step with massive impact on structural strength.
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