Concrete floor from floorboards - considerations

[spacey3]

I wanted to gain some opinion on changing from floorboards to a solid floor.

Background - a chimney has been removed and the walls and ceilings have also been stripped back to brick. After some inspecting it seems some odd occurrences have occurred in the house, the floor joists are either rotten, uneven, or simply don't actually bed into the internal brickwork of the house.

While I also wish to install a stone floor and some underfloor heating in this area it was suggested that the simplest thing to do is remove the joints and concrete over.

After doing some research and reading quite a bit I am a little overwhelmed.

The issue - The depth of the void under the boards is around 500mm, the intention is to use the paster from the walls and the tiles in the kitchen along with some brickwork as compacting material to be berried under the boards firstly.

This is where I have differing opinions - I have seen that some use ballast material thereafter to build and even a sublayer before applying membrane, then concrete, then insulation then a screed (this is of course without the underfloor heating).

Others use building sand, what is most appropriate and what are the sizes of each of the layers that should be used?

Oh and the room measures 6.5m long by 3.2m wide.

 

[bernardgreen]

Image the weight of that concrete slab resting on what may be soft earth with a layer of waste plaster and other builder's debris on top. Over time, maybe days, maybe years that concrete mass will slowly sink and with it your floor. That weight will require some sort of foundation resting on stable ground.

 

[spacey3]

Image the weight of that concrete slab resting on what may be soft earth with a layer of waste plaster and other builder's debris on top. Over time, maybe days, maybe years that concrete mass will slowly sink and with it your floor. That weight will require some sort of foundation resting on stable ground.

So what is the suggestion?

 

[bernardgreen]

What is necessary will depend on the type of ground under the house and how far down you would have to dig to find stable soil.

It might be more cost effective to rebuild the floor using all new joists properly seated on ( into ) the main walls of the house.

In the garden of a house a friend is thinking of buying is a shed. The concrete top of the concrete base is an inch or two below ground level due to the "builder" not doing the ground work properly

 

[spacey3]

It is around 500mm in depth and you would need to dig out another 200mm to get to stable soil. I was also looking at alternatives such as lime screed.

 

[JohnD]

The person who suggested using rubble and plaster waste is presumably unaware that plaster will make concrete crack and bulge, and is very very unsuitable for foundations.

 

[theprinceofdarkness]

The cheapest option is to rebuild the existing floor, not putting the ends of the joists into the damp walls, but to support the joists on sleeper walls/ pillars standing on paving stone on the original soil that has been compacted scraped away to a more solid layer.
If you really are set on a stone floor, you could remove the loose material and set down hollow concrete blocks with their flat surfaces down wards, this would give you an extremely strong yet comparatively light way of filling 9" of your void depth. Then a screed of 3", then 4" of foam, then a top screed of 3" then 3" for your yorkshire flagstones. Wow that's 22 " !!!, you could replace one or both of your screeds with 22 mm P5 T&G chipboard.
Frank

 

[spacey3]

The cheapest option is to rebuild the existing floor, not putting the ends of the joists into the damp walls, but to support the joists on sleeper walls/ pillars standing on paving stone on the original soil that has been compacted scraped away to a more solid layer.
If you really are set on a stone floor, you could remove the loose material and set down hollow concrete blocks with their flat surfaces down wards, this would give you an extremely strong yet comparatively light way of filling 9" of your void depth. Then a screed of 3", then 4" of foam, then a top screed of 3" then 3" for your yorkshire flagstones. Wow that's 22 " !!!, you could replace one or both of your screeds with 22 mm P5 T&G chipboard.
Frank

Are you referring to the method they use in building new houses where the ground floor appears to be made of thermo blocks? Then screed on the top of these blocks?

My secondary or I should say main concern in any method is damp that may rise from the floor especially if you don't have DPC running through the house like a modern build, thus pushing the dampness to the edges of the room and causing it to rise up the wall.

 

[theprinceofdarkness]

Providing what ever you use to fill the void is not touching the walls (1" gap?) then the existing wall damp course will stop rising damp. You could use Celcon blocks laid over a DPC to fill the void. You would not need to use the foam then. So that would be 1" mortar followed by loads of Celcon blocks laid flat side downwards, then 3" screed and 3" yorkstone flags. Seems to be a good time to do some pricing up. In general Celcon blocks do crack and are not as stable as concrete ones. You can get them as thin as 2", could be useful in making up a little depth error.
Frank

 

[spacey3]

Thanks, I am inclined to go with a limes screed floor cost wise isn't a huge difference in materials, what you pay for one you pay for another.

The question is getting it right from the outset rather than having issues further down the line.

 

[Nige F]

Re Lime screed - is that the same as Lime concrete? I saw a Grand Designs once and they went for eco lime concrete and it was a disaster !

 

[spacey3]

Re Lime screed - is that the same as Lime concrete? I saw a Grand Designs once and they went for eco lime concrete and it was a disaster !

No I don't believe it is.

 

[theprinceofdarkness]

There is a product called " Limecrete" which is little hollow clay balls in a lime mix. Its meant to added some insulation. Do you intend to fill the whole void with this product? See :- https://www.lime.org.uk/products//limecrete-and-sublime/labc-registered-sublime-limecrete-floor/
Note the french drain to sort out the damp!
Frank

 

[spacey3]

I saw that one, was considering that. Have arranged for a structural engineer to take a look at things - then take things from their, might need some wall ties since the upper wall has some movement in it.