Concrete Levelling near you

Approved Document C, the 2004 edition incorporating the 2010 and 2013 amendments and marked for use in England, is the guidance a new or reinstated ground floor is judged against. It states that floors next to the ground should resist the passage of ground moisture to the upper surface of the floor, should not be damaged by moisture from the ground, should not be damaged by groundwater, and should resist the passage of ground gases. Wales publishes its own Part C guidance, Scotland works to its building standards handbooks and Northern Ireland to its own technical booklets, so check your own country's document rather than assuming the England version applies.

The technical solution it sets out is worth knowing, because it tells you what should be under your feet. A concrete ground supported floor may be built with a well compacted hardcore bed no greater than 600mm deep of clean broken brick or similar inert material, free from water-soluble sulphates in quantities that could damage the concrete; concrete at least 100mm thick, thicker if the structural design requires, to mix ST2 in BS 8500, or to mix ST4 where there is embedded reinforcement; and a damp proof membrane above or below the concrete, continuous with the damp proof courses in the walls. Where the ground could contain water-soluble sulphates, the membrane should go at the base of the slab.

Two practical consequences follow for a levelling job. First, if the floor has to come out, the replacement is a designed build-up rather than a slab poured to whatever thickness fits, and the membrane has to be lapped and sealed into the wall damp proof course rather than stopped at the skirting line. Second, if the existing floor is damp, adding an impermeable covering over a levelling compound traps the moisture rather than solving it, which is why a fitter who tests the base before quoting is worth more than one who does not.

Breaking out a ground floor is one of the few domestic jobs that opens a direct path between the subsoil and the inside of the house, which is why Approved Document C treats ground gas as a floor issue. It describes radon as a naturally occurring radioactive, colourless and odourless gas formed by radioactive decay wherever uranium and radium are found, notes that it moves through the subsoil and into buildings, that some parts of the country, notably the West Country, have higher levels than elsewhere, and that exposure to high levels for long periods increases the risk of developing lung cancer.

The document says that to reduce that risk all new buildings, extensions and conversions built in areas where there may be elevated radon emissions may need to incorporate precautions, and it points to BRE Report BR 211 for whether an area is susceptible and what protective measures are appropriate. It sets out the thresholds BR 211 works to: basic radon protective measures in areas where 3 to 10 per cent of homes, and full protective measures where more than 10 per cent of homes, are predicted to have radon at or above the Radon Action Level of 200 becquerels per cubic metre. The maps in BR 211 are based on the indicative atlas published by the health agency and the British Geological Survey.

For a homeowner the point is narrow and useful. If you are having a solid floor taken out and recast, and the property is in an area flagged for radon, that is the moment to ask whether a gas resistant barrier is being incorporated, since the same membrane can serve as the damp proof membrane and the cost of including it while the floor is open is nothing like the cost of retrofitting it afterwards.

Levelling compound is the right answer for small deviations over a sound, dry, clean base. It is thin, it goes off quickly, and it gives a floor covering the flat surface its manufacturer asks for. What it cannot do is add strength, bridge a moving crack, or cure a damp floor, and spread thickly to make up a large step it will craze and break up. If a contractor proposes to make up thirty or forty millimetres with a compound designed for a few, that is a specification question worth pressing.

A screed is the answer where there is real depth to make up and the height is available. It is heavier work, it takes far longer to be ready for a covering, and the drying time depends on thickness, mix, temperature and ventilation rather than on a number of days anyone can promise in advance. The right commitment from a contractor is that the screed will be tested before a covering is laid, and that the result will be recorded.

Breaking out and recasting is the answer when the problem is the floor rather than its surface: a damp slab with no working membrane, a slab that has settled because the ground beneath it has, or a floor that needs insulation to be worth heating. It is the most disruptive option and the only one that lets you put the build-up right, including the membrane, any gas barrier and the insulation, and get the level correct in a single operation rather than layering corrections on top of a floor that was never sound.

It starts with measurement rather than material. A laser or a long straight edge establishes where the high and low points are and how much total deviation there is; the floor is tapped and probed for hollow or friable areas; the moisture condition of the base is tested rather than judged by eye; and the available height is checked against door bottoms, thresholds, stair bottoms and the level of the damp proof course in the surrounding walls. That last check is the one that gets skipped, and raising an internal floor without thinking about it is how a perfectly good wall starts showing damp.

Preparation then does most of the work. Old adhesive, paint, laitance and dust are removed mechanically rather than swept, since almost every failure of a levelling compound traces back to a base that was not properly prepared. Cracks and hollow areas are cut out and made good, movement joints in the existing slab are identified so they can be carried through rather than buried, and the base is primed as the product requires.

Application and drying complete it. The compound or screed is mixed to the stated water content, placed and worked in the thickness it is designed for, and protected from draughts, direct heat and traffic while it sets. The floor is then allowed to dry, tested, and only then covered. Where underfloor heating is present, the commissioning sequence matters and should be written into the quotation rather than agreed on the day.

Depth and preparation drive this price far more than floor area does. The things that move a quotation are how much deviation there is between the highest and lowest points, what has to be ground off or cut out before anything is laid, whether the base needs priming or a bonded system, the moisture condition of the slab and whether a surface membrane is needed, whether the build-up can be accommodated under existing doors and thresholds, and how the material gets into the room, since pumped flowing screed and hand-mixed bags are different operations. Outdoors, access for plant, the depth of the base and where the water is supposed to go matter most.

This is a job worth quoting more than once, and LokalMatch makes that quick. You set out the floor once with your postcode, the room sizes, what is on the floor now, what is going on it and what you know about damp or movement, and flooring and concrete contractors covering your area respond to you directly. Homeowners are not charged; the trades pay for the requests they receive. LokalMatch does not lay screed, does not set prices and does not vet, rank or recommend the contractors who answer, so the moisture testing, the specification and the guarantee remain for you to check.