Guide Sheet – Limecrete Floors

Limecrete Floors

  • Carefully dig the old floor out, being careful not to start move the foundation stones, if they are sticking into the room dig into the room at a 45 degree angle.
  • Ideally you need a minimum of 150mm of compacted foam glass (195mm loose), this can be deeper if lower U values are required.
  • Make sure the soil is solid with no soft spots, set up a spinning laser to get your depths correct. If the ground is uneven there is a good chance you’ll use more foam glass.
  • Lay the geotextile membrane on the floor and go up the walls with it.
  • Try to keep the bags of foam glass upright, put a sheet around them on the floor, then two people hold a sheet approx. 2msq and a third person split the bag from the top, the foam glass should then fall into the sheet.
  • Tip the foam glass into the room, if you installing more than 300mm compacted foam glass you will need to compact the floor in two separate layers. Under 300mm can be compacted as a single layer.
  • Use a medium size whacker plate 80 – 100kg, make sure you get a good firm and level floor, otherwise you could easily be putting down a thicker lime screed.
  • Once firm, place the membrane over on top of the foam glass and fold it up the wall approx 150mm.
  • If installing UFH, lay the Geogrid mesh on top of the membrane, put some weights in the corners to keep the mesh in place. Then attached clip rails to the grid with cable ties ready for the UFH pipes.
  • Depending on foundation stones, you can put cork boards around the external perimeter walls, use a saw/small grinder to cut the boards down to 100mm strips.
  • Lime screed, set the laser up to do a 100mm lime screed.
  • 4 people should manage about 25m² a day, ideally you have 3 mixers going. Belle mixers can manage but the Baron Mixers are far superior, quicker & safer and make a better mortar.
  • Mix 2.5 sharp sand with 1 part NHL – either NHL3.5 or NHL5 as standard. This is done via buckets, make sure you are using equal measures throughout. Firstly mix the sand and lime dry so it gets a good mix before adding water. Add water slowly and keep adding water when necessary. Add fibre for the last few minutes, the mortar should be in the mixer for around 20 minutes. Don’t make it too wet, the mortar should be able to make a ball if put into your hands and not fall apart.
  • Mortar should be tipped in each corner when you start at one end and levelled off with a plastic float via the laser, work your way back. If not finished at end of day, finish with a 45 degree angle where you can rejoin next day. If putting a stone floor on top leave it quite open pore texture so bedding mortar can stick to it easily.
  • There’s a good chance you will be able to walk over the screed the following day, but ideally lay a board over so you do not damage the screed and lift it of an evening.
  • Calculations needed: to get a loose depth times the compacted depth by 1.3
  • For the NHL quantities, times the floor area by 1.4 to obtain quantity needed for a 2.5 : 1 mix ratio.

Example U-values based on 50m² with 25m exposed perimeter

U ValueLoose DepthDepth after Compaction
0.32 W/(m²K)156mm120mm
0.28 W/(m²K)195mm150mm
0.24 W/(m²K)260mm200mm
0.21 W/(m²K)325mm250mm
0.18 W/(m²K)390mm300mm
0.15 W/(m²K)520mm400mm

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