Good concrete: what to ask before the pour

What does the concrete grade mean?

You may see labels such as C20 or C25 on a quotation or drawing. They describe strength requirements, but the notation depends on the specification being used. Ask your engineer and supplier to confirm they are referring to the same requirement.

A higher number is not something you need to buy for every part of the house. The engineer chooses concrete for its purpose, including the conditions it will be exposed to.

Why counting bags is not the whole answer

Concrete is made from cement, water, sand and stone. The familiar mix ratios describe the proportions of materials, but the result also depends on their quality, accurate measurement, water content and how the concrete is handled.

Ask how each batch will be measured and checked. For ready-mixed concrete, keep the delivery information and confirm it matches the order. For concrete mixed on site, the team still needs a controlled method and a testing plan.

Water has two different jobs

Water is needed to make concrete. Adding extra water simply to make the mix easier to spread can weaken it. The team should follow the agreed mix and get advice if it is difficult to place.

After placing, the concrete needs protection from drying too quickly. That is a different task from adding water to the mixer. It helps the concrete develop the properties it was specified to achieve.

Looking after new concrete

This is called curing. It means maintaining suitable moisture and temperature while the concrete develops. The method may involve wet coverings, protected surfaces or other measures specified for the job.

Ask who is responsible, what method they will use and how long it must continue. Have the materials ready before the pour. Occasional watering is not a substitute for the agreed curing plan.

Check the materials and storage

Cement needs protection from moisture. Sand and stone need to meet the specification and be kept free of contamination. Water used for mixing also needs to be suitable.

If materials arrive damaged, contaminated or different from what was ordered, flag it before they are used. Buying early only saves money if materials remain suitable when the team needs them.

How will you know it meets the requirement?

Concrete samples can be made into cubes or cylinders for laboratory testing. The project specification sets out the sampling, storage and testing arrangements. Ask which pour each result relates to and keep the reports.

A low result needs investigation by the engineer. It does not automatically tell you that everything must be demolished, and it should not be ignored because the concrete looks hard.

Getting the concrete into place properly

The team needs to place and compact the concrete around the steel without leaving gaps. It also needs a plan for interruptions, equipment problems and difficult access.

If rough, stony gaps appear when the moulds are removed, ask for them to be assessed before they are covered. Their depth and position matter when deciding what repair is appropriate.

Questions worth asking before the pour

• Has the engineer’s required inspection been completed?
• Are the steel, openings and temporary supports ready?
• Is there enough concrete or material to complete the planned work?
• Who will take the samples and keep the records?
• What is the plan if equipment fails or the weather changes?
• Who will look after the concrete afterwards?

Ask these questions early enough for the team to act on them. A calm check before the pour is much easier than trying to resolve uncertainty while the concrete is arriving.