Concrete on floorboards

[sandy10]

Hi,

I'm planning to create a concrete hearth to the front of my fireplace, which will continue inside the fireplace allowing me to have a nice fresh upstand to tile.

The constructional hearth is 750mm wide x 330mm deep.

I want to make the concrete hearth extend to the full width of the fireplace which is 1200mm (ie 450mm - 225mm extra to each side of the constructional hearth.

Would it be possible to concrete over the floorboards by 225mm? if so, do I need to apply some PVA etc to make them adhere better?

I'm planning to pour to a depth of 70mm, so effectively each end on top of the floorboards will be 225 x 35 x 70mm so not a huge weight.

Thanks

 

[regsmyth]

Not quite sure if you're right with your measurements - I can't quite understand where your 35mm fits in.
I don't see any great problem with what you propose, but it wouldn't be considered good practice.
If you need to get a board up, for example, you might crack your concrete.
You'd be better of cutting your floorboards back and maybe fitting new supports for the board ends.
But it's all a bit dodgy really. Can't you just keep the concrete the same size as the hearth?

 

[sandy10]

Not quite sure if you're right with your measurements - I can't quite understand where your 35mm fits in.
I don't see any great problem with what you propose, but it wouldn't be considered good practice.
If you need to get a board up, for example, you might crack your concrete.
You'd be better of cutting your floorboards back and maybe fitting new supports for the board ends.
But it's all a bit dodgy really. Can't you just keep the concrete the same size as the hearth?

Apologies, it's 350mm.

IF a board needed to be raised (it's having engineered timber laid over the floorboards anyway) it will cause disruption anyway.

 

[regsmyth]

Ok, I assume the new flooring will butt against your concrete.
You're laying the floor before sorting out the hearth?

Its the issue of having a combustible material underneath what will be considered a solid, fireproof lump of concrete. Just not very clever.

But if you do it anyway, I would put several screws into the floorboards and leave the heads well out so the concrete can hold onto something. I might also put some steel mesh in to help prevent cracking, particularly in the bit over the floorboards.

Yee ha!

 

[sandy10]

Ok, I assume the new flooring will butt against your concrete.
You're laying the floor before sorting out the hearth?

Its the issue of having a combustible material underneath what will be considered a solid, fireproof lump of concrete. Just not very clever.

But if you do it anyway, I would put several screws into the floorboards and leave the heads well out so the concrete can hold onto something. I might also put some steel mesh in to help prevent cracking, particularly in the bit over the floorboards.

Yee ha!

Hi Reg

The floorboards I would cover are OUTSIDE the requirements of Building Regs - ie they are more than 225mm tucked around the face of the opening. The rest of the concrete will sit on the constructional hearth, so really the end bits are for aesthetics only, in making the new hearth sit right to the edges of the brick fireplace.

No - the flooring is going to be fitted after - I know the floor + underlay will be 17mm, so have calculated the upstand accordingly. The floor can then be cut in around my work and prevent me damaging it!