Slate hearth in upstairs bedroom

Chucklechops

Hi there,

I own a terraced cottage, and I'm installing an electric stove in my main bedroom, against the closed fireplace.

On lifting the carpet, I've found the old concrete hearth, which I understand is fairly common in these types of property.

I intend to put a piece of slate on top of the concrete, which measures 80 x 50 cm, and is 3 cm thick. It's heavy, but not excessively (I'm able to lift it).

My concern is, will it be too heavy? I very much doubt it, as I can stand on the concrete section, and I'm many times heavier than the slate. Plus, I have a water cylinder in the room which will be heavier still.

But I just thought I'd check to see if anyone can foresee any potential problem here.

Many thanks for any guidance.

daivid

Too heavy for the concrete underneath- no, too heavy for the beams - no, far lighter and better distributed than many typical loads in an upstairs room.

stuart45

Will be OK as long as your concrete hearth is stable. The old ones were often held up by a brick trimmer arch under the concrete.

casper_gutman

It will be fine. It's lighter than a wardrobe, and much lighter than an occupied bed.

Imagine a king-size framed bed with two adult-sized people in it. Much of the weight is supported on two points under the legs, out in the middle of the room well away from the areas where the floor structure is supported by the walls. Without wishing to be too graphic, the two occupants of the bed won't always lie still, either! Your piece of slate will be much less onerous for the floor structure to support than such a bed, as it will be close to the wall (and the strongest part of the wall, around the chimney breast, at that), lighter, will rarely if ever see the weight of even one person, and will have its weight well distributed by a bed of mortar rather than standing on small legs. No problem at all!

stuart45

An upper floor concrete hearth in an old house can be the weakest part of the floor. If the trimmer arch is in poor condition it doesn't take much to knock them out. The Kango makes short work of them.

casper_gutman

stuart45 said:

An upper floor concrete hearth in an old house can be the weakest part of the floor. If the trimmer arch is in poor condition it doesn't take much to knock them out. The Kango makes short work of them.

Fair enough, you clearly have experience in this area, and there would be no harm in being alert for signs of deterioration of the structure. That said, this isn't only an issue because the OP wants to place a piece of slate over the hearth. Just standing in that part of the room would probably be more risky!

I would cautiously suggest that a structure being easy to demolish isn't always the same as it lacking strength as such. A structure like an arch can be very strong in resisting vertical load while also being very easy to destroy if hit at an angle. The concentrated dynamic load from a Kango is quite different from the evenly distributed weight of a slate hearth!

stuart45

I agree that an arch when properly built is very good at taking loads. However, a lot of trimmer arches were only half of a segmental, rough ringed arch, with only one ring. The top would be sprung off the trimmer joist, and in time with any movement in the timber the brickwork would start to drop. When gutting an old house and ripping out the ceilings, you can see what poor condition some of them are in. 
In more recent years, rebar in a concrete slab, built into the brickwork made a better job.
Saying all of this, a piece of slate on top will probably be fine, but it's worth people knowing about the way their house is constructed.

stuart45

These pics might help.

plumb1_2

stuart45 said:

An upper floor concrete hearth in an old house can be the weakest part of the floor. If the trimmer arch is in poor condition it doesn't take much to knock them out. The Kango makes short work of them.

And usually a weak mix 

casper_gutman

stuart45 said:

These pics might help.

They really helped me! Thanks for looking them out.