Expert: Roger Zona - 8/4/2011

Question
Hello Roger

I'm trying to research the best method and design for replacing the floors in old stonewalled houses with new concrete slabs.

I have a number of smallish old properties in Southwest France  that need new floor slabs inside.

The houses are of basalt stone and mortar construction.
The walls construction varies from finely dressed stone and proportionately little mortar to rougher uncut stone and relatively higher proportions of mortar.

The walls are generally massively constructed and anything from 500mm to 800mm thick.

Original floors are generally 6x7 metres and are/were wood supported on pine beams and in most properties now have the modern DIY addition of a 50mm scree and tile finish.

One idea I have been considering is using epoxy fixed Gewi bar ( a German rebar type use in the mining and geostabilisation industries) epoxied at 200mm depth into the walls to fix 100mm steel angle round all 4 walls.

Gewi bar varies in diameter and loading capacity  but to give you an idea the shear load of a single 16mm bar has been quoted to me at 5 tonnes

Originally my idea was that that angle fixed in this manner would form the support for precast concrete floor beams (working 1 way)

I'm now wondering if this system could serve as permanent form work and support on all four walls for a poured concrete slab?

Would this be a safe way to transfer the load of the slab into the walls of such a property without the need for additional beam or column fabrications?

Many thanks for any thoughts

Answer
Hello Karim

You didn't say how old the houses are but, by your description, I assume they may be pre-WWII or older.  That being said, it would not be wise to expect the existing foundations to support the transfer of the floor slab.  I am not familiar with the German system you refer to.

It may be prudent to hire a structural engineer to exam the houses and, if necessary, conduct some tests to determine the safe load transfer that the existing foundation would support.

Also, if there is a governing agency (building department) in the city or province where the houses are located, they can give you advice regarding the structural system you describe or perhaps recommend another system or method that is approved.

Thank you for writing and I hope this was helpful.

Roger
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