Installing constructional hearth

[JONXLR8]

I've recently uncovered and opened up the fireplace in our living room.

Upon digging out all the backfill i've come to realise there's no solid constructional hearth, the concrete floor ends at the fireplace opening.

I've dug out 2" below the concrete floor so far and can see what I guess used to pass for a hearth which is (was) a layer of crumbly concrete which I've now removed. All that's there now is some thin bits of slate and under that smallish pebble stones. At the back right hand corner of the fireplace as you may be able to see in the photos, is some fairly tough mortar up against the brickwork.

What I'd like to know is:

How far do I need to continue digging down?

What are the layers of materials that I need to put in, in what order and in what thicknesses? Is it gravel, sharp sand then cement?

Do I need to put a DPM in there and if so, under which layer and any recommendations?

What type / mix ratio of cement should I use and are there any ready mix products that I could buy?

How much of each material am I likely to need? Opening is 1070 x 570 mm

For info, my plan is to finish the constructional hearth up to the concrete floor level, then put a 40mm thick superimposed slate hearth on that ready for the stove.

Thanks for reading and hope you can help.

Untitled

• JONXLR8
• 30 Sep 2011
• 1

Untitled

• JONXLR8
• 30 Sep 2011
• 1

Untitled

• JONXLR8
• 30 Sep 2011
• 1

Untitled

• JONXLR8
• 30 Sep 2011
• 1

 

[Richard C]

The info you need should be in here;
http://www.stovesonline.co.uk/stove-hearth-size.html

Also read/follow the rest of the links below;
--------------------------------000000000000000000000-----------------------------------------

As this comes up so often, I’ve put together this generic post; read the links but not all may apply to you.

You can DIY but you need to understand the Building Regs (which changed in October 10), submit a Building Notice & pay a fee. Your LABC will inspect &, assuming everything is OK, issue you with a compliance certificate; the BI may want also to witness smoke & spillage tests.

Lots of archive threads on this, & other things you have to watch out for, here a few links for you to read:
http://www.stovesonline.co.uk/stove_building_regulations.html
http://www.hetas.co.uk/public/certificates.html
http://www.solidfuel.co.uk/pdfs/buidling_regs_consumer leaflet.pdf
//www.diynot.com/forums/viewtopic.php?t=183614
//www.diynot.com/forums/viewtopic.php?t=211524
//www.diynot.com/forums/viewtopic.php?t=242738
//www.diynot.com/forums/viewtopic.php?t=224751

Some more sobering links in case you think it’s all a load of old tosh:
http://www.solidfuel.co.uk/main_pages/news.htm
http://www.dailymail.co.uk/news/art...wood-burning-stove-leaks-carbon-monoxide.html
http://www.eveningnews24.co.uk/news/warning_over_heaters_after_norfolk_couple_s_death_1_811099

By far the easiest/safest route is to use a registered HETAS installer who will do all the necessary work, commission the stove & provide you with a certificate of compliance. You can use one of the many stove shops around but you will find it much cheaper to employ an independent installer who is happy for you to source your own stove, liner & ancillaries & even undertake the necessary building work but do check with them first. You can download a list of local installers here;
http://www.hetas.co.uk/nearest_member

Get at least 3 quotes & you might be pleasantly surprised; you should ask yourself if you really want all the hassle & risk getting it wrong & climbing onto a roof with an 8M stainless steel snake on your back is not for the feint hearted!

 

[JONXLR8]

Thanks for your reply Richard, we will be using a HETAS installer to fit the stove, register plate, flue, pot and certify it but I wanted to save a bit of money by getting the hearth and brickwork sorted first.

I've had a look through some of the links you posted but a lot of them are about rendering the brickwork which is something we don't want to do.

The stovesonline guide says:

If the hearth is on a non-combustible floor (for example and concrete floor slab) then the total thickness of the hearth and of the non-combustible floor must be 250mm or 125mm thick with a 50mm air gap underneath

There's no air gap to speak of as it's a solid floor in the living room, so based on the above if my slate hearth is 40mm my constructional hearth must be at least 210mm thick. Have I got that right? Does that mean the concrete needs to be 210mm thick or does that measurement include the sand and aggregate below it (if that's what I need) as that is obviously non-combustable also?[/quote]

 

[Richard C]

See here;
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADJ_2010.pdf
Page 37 clause 2.2.4.

So 125mm thick in total as long as there is no combustible material directly underneath the hearth. Personally I would lay a 150mm constructional hearth with the 40mm slate hearth over the top.

 

[JONXLR8]

Brilliant, cheers. I'll get digging.

I've been looking at Hanson dry mix cement, just add water stuff. They've got multi-purpose concrete, instant concrete and 40N concrete, does it matter which one I use? And do I need to put a steel re-bar or mesh in there to reinforce it?

Also, worth me putting a DPC down before pouring?

 

[Richard C]

I've been looking at Hanson dry mix cement, just add water stuff. They've got multi-purpose concrete, instant concrete and 40N concrete, does it matter which one I use?

Ready mix is a bit of an expensive way of doing it but for small amounts I suppose it saves a bit of hassle as long as you can find the right mix. The constructional hearth will be subject to relatively high heat so you don’t want anything too strong or it will crack. You need a mix that will withstand around 100 degrees C or so & it’s usual to use a lime mix for concrete & render; 4/5:1:1 - sand/lime/cement. Looking a the Hanson range they don’t say what’s in it but all the temperature ranges cut off at 35 degrees which doesn’t sound quiet right & is a bit worrying!

And do I need to put a steel re-bar or mesh in there to reinforce it?

No steel; if anything it will cause more problems in higher heat applications as the thermal expansion of steel is greater than concrete = cracks.

Also, worth me putting a DPC down before pouring?

Not sure how much use it would actually be; chimneys in older properties tend to be in the centre of the house & your unlikely to find any damp in the oversite that far in but for the sake of a bit pf plastic you might as well. A modern property should have a DPM under there somewhere anyway.