How to concrete a floor

How to concrete a floor

Fancy a chic new polished concrete floor in your kitchen? Is your old timber floor rotten and in need of replacing? If you’ve got a good grasp of DIY, the right tools and a can-do attitude, read on.

You will need:

  • Sharp sand
  • Cement
  • Aggregate
  • Rubble or scalpings
  • Polythene damp proof membrane
  • Damp proof membrane jointing tape
  • Polystyrene insulation boards
  • Bonding agent
  • Trowel
  • Wacker
  • Wheelbarrow
  • Bucket
  • Shovel
  • Tarpaulin or polythene
  • Fungicide
  • Length of timber approx. 1m x 10cm
  • Timber battens 600mm x 38mm

One of the first things you should consider is whether your new concrete floor will bury or ‘bridge’ your existing DPC (damp proof course). If this happens you’ll need to call in the professionals to inject a new damp proof course with a 30 year guarantee for survey and mortgage purposes.

IMPORTANT: Note that your new floor may also bridge your neighbour’s DPC. The Party Wall Act states that you must ask your neighbour’s permission before doing any work that might affect a party wall. Failure to do this often results in costly legal proceedings; you have been warned!

Step 1: Preparation

Make life easy for yourself by removing the door and skirting boards to allow for hassle-free access. If you’re replacing a timber floor make sure there is no dry rot in the original floor which could appear at the edges of the new concrete damaging skirting boards and joinery. All debris must be removed and the subfloor treated with a fungicide. It’s a good idea to treat the walls below ground level too.

Now take a piece of chalk and draw a level line all around the room to show where the finished floor level will sit. Obviously if your concrete will be covered with tile or wood blocks you’ll need to allow for their thickness. 50mm below this draw a line to show where the screed will sit. 100mm below will show the thickness of the concrete layer and the final 50mm below that will show you where the insulation board should sit. Anything below this line will be a mix of infill and sand.

Step 2: Adding infill

The next step is to roll out your damp proof membrane over the bed of sand leaving enough allowance to reach the height of the finished floor. If the membrane isn’t wide enough to fit the room you’ll need to join two pieces together with special waterproof jointing tape, overlapping by 200mm.

10% of a building’s heat is lost through the floor so it’s important to insulate adequately. Lay polystyrene insulation boards (Kingspan or Celotex for example) making sure they’re securely joined and go right up to the edges of the walls without any gaps. Now is the time to add any underfloor heating pipework.

Step 3: Adding the damp proof membrane and insulation

The next step is to roll out your damp proof membrane over the bed of sand leaving enough allowance to reach the height of the finished floor. If the membrane isn’t wide enough to fit the room you’ll need to join two pieces together with special waterproof jointing tape, overlapping by 200mm.

10% of a building’s heat is lost through the floor so it’s important to insulate adequately. Lay polystyrene insulation boards (Kingspan or Celotex for example) making sure they’re securely joined and go right up to the edges of the walls without any gaps. Now is the time to add any underfloor heating pipework.

Step 4: Adding the concrete

As a general rule of thumb go with 1 part cement, two parts sand and three parts aggregate. Work out exactly how much of each you’ll need using this handy concrete mixing calculator. And now the fun bit, the mixing. Remember not to add too much water as you want it fairly stiff.

Start at the wall furthest from the door and lay the concrete in strips flattening it out with your length of timber so it’s level with your second chalk line. Keep checking with a spirit level laid on top of your timber. Cover your damp concrete with polythene or a tarpaulin and leave for three days.

Step 5: Adding the screed

The final step is adding your top layer, the screed, to smooth out any imperfections and give you a lovely flawless surface like the baize of a snooker table. To do this you’ll need to create a ‘framework’ of timber using 38x38mm battens, the top of which should be flush with the top chalk mark. DIY merchants sell self-leveling compounds which make the job easier than mixing yourself. Fill in between the timber battens, leveling with a trowel so it’s completely flat. When you’re satisfied that the screed is smooth and level, remove the battens and fill the gaps with the mix. Cover with polythene and leave for up to one week.

Finally, trim the damp proof membrane and replace the skirting boards. Now open the fridge and treat yourself to something cold and fizzy.

Contact us

Get in contact with the right person to answer your queries, or just talk to us about how we can help you and your family.

Preparing your home before a storm

With a little preparation you could help to reduce the potential for damage - and save yourself some money and stress in the process.

Aviva Drive

Safer drivers scoring 7.1 or more save an average of £170, a saving that can be achieved by 52% of them.


Back to top