Home-made storage heater Part 3 - Contructing the wall cont...

Having done as much of the planning as possible and with all my beautifully washed stones at the ready, I was now all set to begin the build. If you missed the first part of this build it can be found here

Start of construction - mass heater

 Start of build - natural storage heater 

I laid down a bed of mortar over the whole of  the strawcrete block’s upper face and placed the stones on it, tapping each stone into the mortar with a rubber hammer. 

Unlike building with brick I did not attempt to put any mortar on any vertical faces of the stones but instead pushed it into the gaps after the stones were in place, embedding small stones and chippings of stone where possible.

Obtaining optimal thermal conductivity - DIY storage heaterFor the subsequent layers I found I became better at selecting the stones and laid them without the need of too much prior planning. As I mentioned at the end of the last post, I laid stones on the next layer in a front-to-back  orientation, the stones being long enough to have their ends exposed to the heat and touching the rear shuttering, this was so that heat could be conducted through the core of the wall. The other advantage of altering the orientation of the stones on each layer is structural, no vertical mortar joints would be aligned from layer to layer and hence the finished wall would be more stable.

work in progress - building storage heater

Before I started the build I did wonder about the height I would be able to achieve in one day, as I was concerned about the weight of stone and compression on wet mortar. However, after doing some research, I found that the recommended height when working with stone and lime mortar is 1 metre, before leaving to set.. Therefore, I would have been able to complete the build within the day. In effect, with the additional constraints of filming and with the terrible weather, which put us off searching the garden for ‘just a few more corner-shaped stones’,  I actually only completed half of the storage heater on the first day.

I don’t know why but the end result seemed a much higher mass than I had at first envisaged, which of course was all to the good!
Cleaning lime mortar from joints I kept the joints on the front elevation as clean as possible, removing any excess away with the trowel edge. Any mortar that had stuck to the outward facing side of the stone was removed and the residue was cleaned off with a moist cloth. I have however always found that lime mortar stains much less than cement mortar, which is yet another reason, if I needed one, to use it. 

Finishing top of DIY natural storage heater

The wall top was the hardest  to achieve because this is where suitable stones had to be found that would bring the top to a fairly even and flat surface. Again, if I’d been using brick it would be easy to arrive at a flat-topped wall.

Home-made storage heater removing excess lime mortar

After two days I was able to remove the shuttering and lift the panels clear.. The mortar had dried but could easily be cut from where it had flowed onto a stone face behind the shuttering, using the edge of  a pointing trowel. 
Home-made stone storage heater - finished

The mortar was left for another two days to set further. It was then possible to clean any mortar stains off the stone with a wire brush.

Home-made storage heat in action
Natural storage heater - Finished project The stove was lifted back into position, the chimney reconnected and the fire was lit. Normally the stove is lit in the evening, but as we’ve been working in the lounge during the day we’ve been able to maintain a fire in the stove for 8 hours and this has started to impart some of the heat into the new wall.


Home made natural storage heaterThe results to date although subjective have been encouraging, the room certainly takes much longer to cool after the fire has expired. In the morning I would say the room feels warmer than it was inclined to be before the modification but I would like to experience some regular, colder weather before I would attempt to confirm this..


In conclusion, I believe that the heat storage wall has made a difference for very little cost, just the labour hours to make it. It  would probably work as well if one used a wall of fired clay brick,  they could be made to fit exactly into the front to rear dimension of the wall thus furnishing an uninterrupted channel for heat to be conducted throughout the wall thickness.

Now if you'd like to sit back and watch the film. There will be two more posts on this project to cover the chimney sweeping and mixing of lime mortar.

If you've enjoyed this article and found it useful please feel free to share it or to comment and/or make observations. All the very best and until next time,
© Andy Colley 2014

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