DIY concrete hearth for stove

[chriseastlondon]

Hi. I'm getting a multi-fuel stove installed in about 3 weeks. It's going into a fireplace that I've stripped back to the builder's opening.

I need to build the hearth. I think I'm going to make it out of concrete. One option would be to fix batons around the front of where the hearth needs to be and just pour the concrete. But instead I'm thinking of pouring the concrete into a melamime mould, flipping it over and using mortar to fix it in place.

I've looked up the regulations and I understand the requirements for the thickness and how far it needs to extend in front of and around the recess.

I'm a bit confused about what mix to use. I've seen a few different suggestions. Can I use sharp sand and Portland cement? Any advice on the ratio? I was planning to add a dye as well, just to darken it a little bit.

Is there anything else I should add to prevent it from cracking when it's exposed to a high temperature?

Grateful for any advice.

 

[oldbutnotdead]

Standard mix (4 ballast to 1 cement or 3 gravel 2 sand 1 cement), if you're doing at least minimum required thickness it won't crack from heat depending on your stove legs and weight you might want to go a bit thicker.
Shutter it and pour it in situ- it'll be a big heavy lump, odds of you getting it level on a mortar bed are slim to none. Don't forget dpm underneath.
A raw concrete hearth will be hard to keep clean and always dusty. Think about a decorative finish (slate is a favourite, paving slabs have done me ok). Tiles would look good but you'd have to be careful on installation- any gaps in the tile bed and point load could be a disaster.

 

[tell80]

You can buy bagged concrete - just add water and mix in a wheel barrow. Add the dye to the water.

Are you opening up according to the installation dimensions of the Stove Mfr's - HxWxD?
The Width of the back hearth opening needs to be correct before pouring concrete.
The front hearth is sitting on soil and rubble surrounded by a fender wall.
Your floor boards are nailed to the fender wall trimming - some of the nail heads seem to be showing rust.
Rust means damp so its often the case to dig out the front hearth soil/rubble to below the wall plates, and lay a membrane - you can work up from there with concrete.

If you want any more advice on your project just come back.

 

[chriseastlondon]

Thanks for your replies. Really helpful.

The main reason I was hoping to make it in a mould was so I'd get a smooth surface. Could it work if I poured concrete as a base layer - so I dig out the front hearth first, lay a dpm and put down a first layer of concrete to get it level, then cast the surface layer in melamime to get a smooth finish and lay that on top? Would that work?

@tell80 when you say am I opening up according to the installation dimensions, do you mean does the stove fit in the space according to minimum recommended distances in the installation manual? Yes, that was one of reasons I chose the model I did. The installer has checked as well, so hopefully okay.

Would this type of concrete do?

Blue Circle Multi-Purpose Ready To Use Concrete - 20kg | Wickes.co.uk

Blue Circle Multi-Purpose Ready To Use Concrete - 20kg

www.wickes.co.uk

 

[blup]

The hearth is in two parts constructional and superimposed, you are planning the latter only. The alternative is to dig it all out, the joist ends may be built into the hearth in which case new supports will be needed, the ends can be temporarily supported by a car jack. Check for rot and and treat accordingly. Then build a block perimeter add plastic membrane and back fill with concrete to required depth for hearth

Blup

 

[cdbe]

What sort of finish are you after? It could look dog rough. If you want the concrete effect you could use a large format concrete effect tile.

 

[chriseastlondon]

This is the sort of finish I wanted: IMG_4346-950x1425.jpg

I was going to use cement dye to get it a bit darker.

 

[opps]

Watching some videos of concrete worktops being made may help

make concrete worktop - Google Search

 

[chriseastlondon]

I watched a few of those. But perhaps I'm making it too complicated by trying to cast it in melamine?

The picture I posted is from a blog post where they explain how they did it:

DIY Diaries: How to create a concrete fireplace hearth

Our DIY series is this week showing you how to create a concrete fireplace hearth. The step-by-step guide comes thanks to Olivia Likosso.

www.themodernhouse.com

Could I do something a bit like what they did - given I'd have to dig out and damp proof the front hearth first? It's not 100% clear if theirs is still a working fireplace or if it's just decorative. I don't think the back part would give them enough distance from the floorboards if it were used for a real fire, would it? Diagram-25-constructional-hearth-suitable-for-solid-fuel-appliance.jpg

 

[tell80]

chris, yes the blue circle will do. And, seeing you've checked, then the dimensions should also be fine.

You can knock out both back & front hearths at the same time, and set your shuttering for the height you want.
The shuttering goes around the front hearth only - screwing the shuttering to your floorboards would give the most firm fixing but some double sided tapes are great for holding stuff in position.

You"pour" all in one go - front and back hearth together - from the membrane up.
Level off with the top of the shuttering.
When the pour is finished, tamp down esp.at the edges.
Run the steel trowel down between the shuttering & the concrete while lightly vibrating the shutters - this will create a clean look.
Use your spirit level across the shuttering and to the back hearth to level off the surface.
Use a float or block of wood to rub up the surface after about 40-60 mins.
When the concrete is green, carefully remove the shuttering, and use a stone to round the corners and smooth all surfaces.

 

[tell80]

The fireplace back needs wire brushing clean of all soot, & the flue needs sweeping.
There will be work at the stack dropping & fixing the SS liner.

 

[chriseastlondon]

That's great. Thank you.