How to lay concrete foundations

Laying a concrete foundation is at the heart of any building project. And in Cornwall, where the coastal climate can be as unforgiving as it is beautiful—that foundation has to be rock solid. With over 25 years of experience laying foundations in Cornwall, we've learned what works-and what doesn't.

That's why we're going to walk you through the essential steps for laying a concrete foundation here. We'll share some local tips specific to Cornwall, and offer advice on how to make life easier for the block layers and other trades that come after.
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First things first: getting your foundation right from the start.

Setting Out Your Foundation

You start by marking the boundaries of your foundation on the ground. That's where accuracy really counts. If the foundation is off, everything else can be affected. In Cornwall, where the ground can be uneven and the weather unpredictable, that means getting it right the first time.
To set out the foundation, use string lines to measure and mark the perimeter. The lines should be taut and level. Measure from existing reference points or gridlines on your plans to ensure the foundation lines are square and the right dimensions. Don't worry if that sounds a bit technical - it's just a matter of getting the measurements right.
Checking for square is also crucial. If your foundation isn't square, your rooms will be out of alignment. And that can cause problems later on with walls, windows and doors. The easiest way to check for square is by using the 3-4-5 rule: measure 3 meters along one side of the corner, 4 meters along the other side, and the diagonal should measure exactly 5 meters. If it doesn't, adjust your lines.
A laser level is your friend in Cornwall's coastal winds and uneven ground. It ensures your lines are straight and level across the whole foundation.

​Preparing the Site for Pouring Concrete

Before you start mixing and pouring, check what grade of concrete you need, you also need to make sure the site is ready. That means digging the foundation trenches to the right depth, as specified in the project plans. In Cornwall, the soil type and weather can vary greatly, so be aware of the local conditions. If the soil is soft or sandy, you might need to dig deeper to ensure a solid base. You might also need to install a layer of hardcore or aggregate to create a stable base before pouring the concrete.
Compacting the ground is next. If the site is damp (and it often is near the coast), installing a damp-proof membrane can help prevent moisture from seeping into the concrete.
Reinforcement like rebar or steel mesh will provide additional strength to the concrete and help prevent cracking later on. That's especially important in areas of Cornwall with clay soils, where ground movement can be an issue.

​Pouring the Concrete

Once your foundation is set out and prepared, it's time to pour or pump the concrete. That's where local knowledge of the weather really comes into play.
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Check the weather before you pour. In Cornwall, the weather can be unpredictable-and heavy rain or coastal winds can affect the curing process. You want to pour the concrete on a day with stable weather-not too hot or too cold. If it's too hot, the concrete can set too quickly, leading to cracks. In wet weather, use tarps or plastic sheeting to cover the foundation to prevent excess moisture from affecting the mix.

Levelling the concrete as soon as it's poured is also crucial. Use a screed board to level off the concrete, filling in any low spots and removing excess concrete. For larger foundations, working with a team to get the surface level quickly before the concrete sets is a good idea.

Edge forms along the edges of the foundation will help hold the concrete in place and create smooth, well-defined edges. These forms will prevent the concrete from spilling out and give you a professional finish.
Making sure everything is square and level is one of the most important steps for ensuring that all rooms will be the same size-and that subsequent trades have an easier time.

When you've poured the concrete and started levelling it, corner brackets or a laser level will help you ensure those edges are square. And that's crucial—slight errors in squaring the foundation can cause walls to be out of alignment later on. That makes life difficult for block layers and other trades.

You need to check for consistency along the entire foundation. Measure at multiple points to ensure the width and length are consistent. That's especially important on larger builds or commercial projects. You want that foundation to be level across the whole site.

​Curing and Final Steps

Once the concrete is poured and levelled, it's time to let it cure. Proper curing is what gives you the strength and durability you need from your concrete foundation. In Cornwall's sometimes dry or windy conditions, keeping the surface of the concrete moist during curing helps prevent cracking and ensures the concrete strengthens properly. Wet burlap or plastic sheeting can help you maintain that moisture.


Concrete usually takes 24 to 48 hours to set to the point where you can walk on it. But the full curing process can take up to 28 days to reach its maximum strength. Be patient—and avoid putting heavy loads on that foundation too soon.


Laying a concrete foundation isn't as straightforward as it looks. Any seasoned pro in Cornwall will tell you that there's a lot of preparation, planning and attention to detail involved. From setting out to ensuring that foundation is square and level, to factoring in the weather conditions unique to Cornwall—you need to get every step right.


That's where local knowledge comes in. By following the right steps and using that knowledge, you can be sure your concrete foundation provides a stable, level base for your entire construction project. A well-laid foundation makes life easier for block layers, bricklayers and any trades that follow. That means the job gets done smoothly and efficiently.


At Concrete In Cornwall, we've been working in Cornwall for over 25 years. We've seen it all. If you need advice or a quote for your next project, we're here to help. We know what it takes to lay foundations right.