Oversite concrete is often reffered to as german floor by the laymen, others mistook it for dpc,however oversite concrete is the mass concrete that you pour to cover the entire lenght and breadth of a building on the ground floor to serve as a source of additional support to the structural stability of a building especially storey buildings.
Is the mass concrete which is cast after the dpc or damp proof course level has been established.
Going by the definitions above it is clear that this portion as part of a building foundation is one of the most important parts of the building.
Not long ago one of my subscribers asked me on how to salvage an oversite concrete that was sinking/collapsing, before then I had also experienced a poorly done job too that resulted in parts of the concrete collapsing, so with the first hand experience and for the benefits of those that haven’t gotten to that stage of your building project is good you read on.
To have a good oversite concrete these are the steps you must take-
(1) Make sure the soil underneath/ or the soil used to fill the dpc is a laterite and not any other kinds of soil especially loose and peat soil. The filling requires sand that can be compacted to have a good sustainability and the ability to carry the compressive load of concrete coming on top of it. A loose soil in this case will not allow the soil to be easily rammed or beat to compaction hence won’t be good for the task.
(2)If it is recommended to use wire mesh or brc by your Engineer then save yourself of future unending agonies with a few thousands of naira and apply it. The wire mesh forms a ring that helps the concrete to be able to carry its weight and even when the soil underneath is getting more compacted, because of the tensile strength of this wire mesh the concrete is most unlikely to cave in, so make sure you spread it round the building as specified.
(3)Also if it was specified in the drawing that you must use a membrane- just call it a polythenelike material that can be able to block water from rising from the soil to the ground floor or slab, then it is important you also do it. this is usually specified where the ground is waterlogged.
(4)Ensure you follow the right mixture ratio of the concrete, hence you may be faced with a not so strong concrete.
(5) Before the day you will cast, make sure you get all the materials you need in place human,materials and otherwise. If the numbers of people you have is not adequate then you may run into problem , some portion will be left till the next day and you may not have a cohesive single bonded foundation.
(6) Take a day get two bricklayers, let them take the proper level of the dpc round and make sure they apply plumb ( an instrument used in determining the level) round the building with the level established and traced with ropes round, when this is done you are most unlikely to have a badly built house. Foundation is the root of the beauty of any house just as it applies to every facet of life.
(7)When you have casted don’t be in a hurry to remove the sideboard or wooden/iron materials that were used to support the concrete from running off the edge, it is good you give it a day to dry before removal else you will notice cracks around the edges when the boards are removed especially when the concrete mixture ratio is weak.
Make sure the iron rods of the columns/pillars coming from the base of the foundation is aligned and shoots out or longer than the top of the concrete by atleast 450mm or 0.45m or 9 inches.
Causes of Caving in /Collapsing oversite/german concrete
(i) When your contractor wants to make profit and save cost, the mixture ratio of the concrete may likely be weak
(ii)When your project has no capable professional directing the affairs on site
(iii)If you are careless or take no cognisance of little details when executing the project
(iv)Soil underneath not well rammed and when it is not a compacting soil that has ability to bond.
(v)During ramming water must be poured again and again until the soil can no longer compact before you stop.
(vi)When the sides of your structure are not well supported by wood or iron and brace properly.
(vii)Damages on site by workers
(viii)When inadequate or substandard materials are used
(ix)The hollow blocks under the concrete if thats what was recommended must be filled with concrete to give the concrete additional support and help to easily transfer the weight to the ground.
Above all, caution! caution! CAUTION!
hope this have helped.