Everything you need to know about concrete floor construction

Familiarity breeds  contempt, which is  why we  take for granted a warm ,dry  and  strong  concrete  floor  under  our  feet. But take it from me, it calls for great workmanship to get that floor ready for the finishing works, such as sand and cement screed or tiles .Anything short of this level of dexterity will leave you with a damp floor and a failing   screed or tiles that needs patching up within a short time. With  this in mind, let me unpack  below ,at  lightning speed, all  that  goes  into  concrete floor construction so that you    may  appreciate  the work and  get  the most  out of floors  by taking good care  of  them. This is important because as we all know, prevention care is cheaper than the cost of repair.

Concrete floors can either be constructed   using ground bearing slabs or pre-cast concrete. Ground  bearing  slabs  are  not supported  by  an external wall, allowing  for  deferential  movements  between them. Construction of the  floor  is a    long  seven step process  that  can take  a minimum of  one  to  four weeks  as  follows:

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  1. First remove the top soil and  vegetable  matter  to  avoid the problems associated   with   slab   movements as  the ground is  compressed  down and  settles in.
  2. Then remove debris  from the foundation trenches and  build the  load-bearing  walls  to  the  damp proof course(DPC) . Note  that  damp proof  course   purpose  is  to  resist  the  capillary  action of  water or  rising damp .Its  cannot be  used  to resolve  high water table  problems at  the  construction site.
  3. Third step, start to construct the floor. Pour a layer of hard-core stones at least 150 mm thick into the floor areas. The hard-core should  consist of  a  wide  range   of stone  sizes  from relatively  big  stones  to  dust or Murrum. This ensures it is compressed   with ease by a vibrating plate or roller. The hard-core  layer  helps prevent  loose  earth  from contaminating  wet  concrete and  to  spread  evenly   the  load  from the  concrete  slab. If  the  hard-core is  deeper than normal,  because  of  excavated  topsoil  or  the site  is  on slope  ,it’s  important  to  cold  compress it  in layers. Failure to follow this recommendation will result in problems as the   consolidation happens later. In the event that  the hard-core is over 500 mm deep, use the more expensive option of suspended concrete floors. This will save you a lot of headache later on.
  4. Then lay a blinding to the hard-core. Large lumps of stones are crushed to form a blinding. Alternatively you can use Murrum or broken bricks which are easily stamped and compacted. Ensure to  keep the  top  of  this blinding    below  the  substructure so  that  the  slabs  can  be  cast  inside  the walls
  5. Lay the damp proof membrane (DPM ), to arrest rising damp from the ground. This membrane  can either  be  above  or  below  the concrete  slab and the  material  used will depend on the  floor finishing  materials . The DPM must overlap with the DPC to isolate the whole superstructure from the substructure.
  6. Second last step-pour concrete slab. The slab should  be  between  100  and  125 mm and  must  of  suitable strength.  If  the ground   below  the  slab  contains some soft  spots, the concrete  can be  reinforced  with a  layer  of  steel mesh. The slab is then tamped and leveled using a timber beam or a vibrator   to remove excess air and water.
  7. Finally allow the  concrete  to  set and  achieve  its  full  strength .  In  hot  weather  protect  the  slab by  watering   it   three  times  daily   for  one    to  two  week(s). In addition you can use  a  polythene  sheet  to cover it  to  minimize  excessive  evaporation of moisture which can reduce the strength of concrete slab and cause cracking. In cold weather, cover the slab with sand to prevent freezing or consider delaying the pouring of slab till when the condition become favourable.
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©Copyright 2017 eastafricaminihardware.com

Sources: The construction of houses by Duncan Marshal and Derek Worthing

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