Building Standards : Ground Floor Slabs

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Concrete Ground Floors and Damp Proofing

The norm in the UK is for concrete ground floors to sit on the soil below them no matter what the foundations. As foundations are usually loadbearing brickwork there is a very small gap between the concrete and the brickwork to allow for minor settlement.

The soil is prepared by leveling and its usually compacted a bit. Then 100mm (4 inches) of hardcore are leveled over the site. The hardcore is broken bits of brick and other stable rubble. Over this goes a minimum of 50mm of sand (blinding) to give a smooth surface. Over the blinding goes 1000 gauge polythene sheet to act as a damp-proof membrane (dpm). This merges with the felt damp-proof courses (dpc) in the walls.

Then the floor is poured as 100mm of concrete. Over the concrete goes 50mm of cement & sand screed to level and finish smooth. Sometimes thinner mesh steel reinforcement is placed in the concrete.

The building site that I’ve been following here in Perak does it somewhat differently.

The soil is leveled and then 75mm (3 inches) of red soil and sand are laid and this takes the place of the hardcore. There’s no sand blinding. Over this goes 75mm of concrete. This is thin construction.

The builder told me that on top of the concrete are the tiles. So there’s no screed.

Amazingly, he said that there’s no damp-proof membrane and blinding. I suppose that if you keep your doors and windows open then any damp which makes it through the floor (or up the walls) will disappear in the wind. Or maybe the tiles keep it out. The wonders of a tropical climate.

I looked around this flat site and there was plenty of water lying in pools from the recent rains. So it’s not as if there was much run-off available. Anyway dig down a couple of feet anywhere and the soil is always damp.

The builders on this particular site did however put in a damp-proof course in the brickwork infill walls. This is a strip of felt usually inserted into brick courses about 150mm above external ground  level. These builders laid it at ground level so it got covered with soil and concrete, and that means it’s useless.

They also put the felt dpc into the garden walls. I don't get it, trying to stop damp from rising in garden walls that are open to the weather.

If you’re buying somewhere you could ask if there are damp-proof membranes and damp-proof courses built-in. Please let me know the answers as I’m sure that they’ll be interesting. And I’d like to know if this construction is typical in Malaysia.

Photograph 1 
Ground beams and red soil & sand “hardcore.”   
Photograph 2
Concrete floor with lots of aggregate and little cement.
Photograph 3
The wooden post is 75mm high for the depth of concrete..
Photograph 4
The finished ground floors, and columns/shuttering for the first floor beams.

Regards, Scott

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Hi.

I was a civil engineer once, so this is interesting for me, but of course in Russia all construction techniques are slightly different.

I think that not doing hydro-insulation is a proof of insufficient professionalism, as constant moisture moving up from the ground will damage the construction. Not as fast as here in Moscow, where one winter could be enough to break a damp wall, but surely after some time.

As to the garden walls you mentioned - there is a difference between moisture that temporarily appears on the surface (due to rain etc.) and moisture that fills all the construction inside. In the first case one can paint the walls, cap them with metal tops etc., and in the second case the construction will inevitably deteriorate in time. So hydro-insulation is always needed.

BR,
Sergey.

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hi, Sergey,

Thanks for the post, and the information. I agree that hydo-insulation is always needed.

Many houses that I've seen have black mould growth which I take to be from rising damp. It's growing upwards on the outside render, and so it's probably inside.

When I've seen damp proof courses inserted they're very low down and have usually been bridged with soil, so they're pretty useless.

Construction techniques here rely on the climate to dry things out, and assume that doors and window will be open. I think that prospective purchasers need to check-out the basic stuff, either visually or with the develper, and by asking a few normally "taken for granted" questions they can get a feel for standards in the develpement

regards, Scott

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Hi Scott:

It is me who should thank you for all the information that is treasured here.

I wonder if that could be possible to make the construction workers to do works according to the standards preferred by the customer? Of course that could be slightly more expensive, but I think that higher standard will result in profit, as with less dampness the building will last much longer, will need less repair and would be better suited for living.
I think this idea of "drying out" is wrong, because if the dampness could be prevented at small additional cost, why bother with much better ventilation? Btw, more active ventilation would have meant much higher air conditioning costs...

BR,
Sergey.

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hi,

If you're designing your own place you can specify whatever construction that you require and then get a builder to price on your specification. You'd need a local architect or an engineer to certify the drawings, and apply for planning permission. You could then supervise the works yourself if you don't mind the hassle.

regards, Scott

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OK, thanks, my wife is a professional designer, and I think I could have managed the supervision part - after all, I had worked for 7 years as a site superviser back in eighties... Thanks. So we have only two problems before us: if my wife and me will like living in Malaysia, and if Malaysia authorities would approve our application, if it comes to that...

BR,
Sergey.