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

  

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.

For 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.

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!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. 

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.

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. 
 

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.

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.

 

The 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

© Andy Colley 2014

RETURN TO GREEN LEVER CONTENTS PAGE FOR MORE ARTICLES  

Home-made strawcrete and stone storage heater Part 2 - building the wall

Looking backwards to go forward, our introduction to storage heaters, came about because we moved down to England from Scotland and bought a wonderful ruin of a 1930’s semi, which had been subject to a whole host of abandoned heating systems, spanning several decades, one of which was an electric storage heater. The start of this project, creating the strawcrete pad can be found here

Previous experience with storage heaters and why we decided to make our own

 

In the front downstairs room of the house, which was to become our dining room, there was was an electric storage heater. This was powered with a low tarif supply but as far as we were concerned it was ugly and inefficient, being placed on the wall between us and the neighbour. We had already decided to remove the sixties era fireplace in this room and replace it with a  cast iron Art Nouveau one we had bought from a builder and open up the chimney.

At the same time the storage heater would be moved upstairs  to a spacious front bedroom, with fine views of Warwick castle’s firework displays, great acoustics for its concerts and which we intended to use as a sitting room. Its function would be to supplement the superb original 30's Art Deco bedroom fireplace. To do this, the heater was isolated from the power supply and dismantled.

If you’ve never seen  what's inside one of these heaters then you ain’t missing much. Basically, they comprise an electrical resistance, running between heavy bricks. The heat output being regulated by a moveable flap to control the warmed air leaving the unit.

The inside rear wall is covered with a pad of insulation. A word of caution: Asbestos was often used as the insulating material in storage heaters and although you will see on many professional websites, dates of 1970 and 1980 quoted as marking the end of its use, you really need to find out exactly if the model you have contains Asbestos before you start taking it apart. Be warned that further to the obvious dangers of Asbestos, this form of insulation, when old can become powdery and thus ever more hazardous to the lungs. It is also of tantamount importance to ascertain if and when Asbestos was banned for use in household appliances/building materials in your particular country of residence. For example, when we moved to our present ruin, here in France, we found that the roofing material on an old abandoned rabbit hutch, attached to a Bread Oven in the garden, contained Asbestos but thankfully,  there were disposal procedures in place, which we could follow to rid ourselves of it.

Far left showing rabbit hutches roof cover, thus prior to Asbestos removal and right a couple of years later on.

 

The key point of our old storage heater’s relocation was that it was to be placed against the internal brick wall of the upstairs room which incidentally led directly onto the stair well. Over a period of days after reconnecting the heater in its new room, we began to notice that this wall had started to store heat as well, such that as one ascended the stairs from the entrance hall, one could feel that there was a significant amount of heat emitted. So although we had known that locating it on an inner wall made sense, we got a much greater benefit from the heater than we’d originally expected. This was a valuable lesson to us of how useful it was to be able to store heat. The means of supply (electricity) was certainly not ideal but the way in which a house could benefit from the simple method of charging up a mass with heat and letting convection do its stuff, was.

Fast forward 20 years and back to our non-toxic storage heater, by appointment to the genius loci

It took about four or five days for the strawcrete to start to feel firm, I was still able to dig into the surface with my fingernail and the surface still felt damp. Nevertheless, I decided to remove the shuttering from around the pad so as to expose more faces to the drier air in the kitchen. 

I also decided to turn the pad upside down exposing the smooth bottom face to the air and I laid the pad onto an old wire shelf from an oven so that air could circulate freely around it.

 
 

After a further seven days, the strawcrete felt firm and resisted my finger nail, it also felt considerably lighter. If you compare the colour with the little pure lime sample you are immediately struck by the warm golden colour the straw has imparted to the lime, something we exploited when we used strawcrete as the foundation layer for our hemp and lime insulated walls in our kitchen.

Work could then progress on making the wall. 

The first thing I did was move the stove off its plinth and sweep the chimney, I’ll describe this exercise in another post. 

 

Next I put the strawcrete into position on the tiled surface, the smooth, flat side down. I had decided to fit shuttering on three sides of the plinth to act as a guide for laying the stones and to prevent excess mortar from the joints from dropping into the gap between the rear wall of the heatsink and the lounge wall. I used chipboard sheets recuperated from pallets for this. The rear wall was a coated sheet but the side walls were bare of any such coating and thus I covered these with a layer of polythene so as not to  draw moisture from the mortar. Across the front elevation I screwed two narrow strips of pallet wood so as to allow me access for laying the stones. 

 

We have plenty of stones in the garden, some are from the house where we have removed parts of walls for windows and doors and some have been dug up over the years of our gardening. I needed stones that had ‘flat’ faces and were fairly regular in shape. The selected stones were cleaned of any soil or clay using a scrubbing brush and water. 

 

Prior to laying the stones in mortar, I first tried various selected ones, altering their orientation until I felt I had achieved the best fit, then removing them and laying them to one side in the same configuration. I’d decided that any large gaps between the stones would be filled with mortar and small stones. The other point in the construction was to lay longer stones front to back so as to conduct heat into the body of the wall, thus certain ones were selected to go onto the next layer. This also would make a strong bond within the wall i.e. there would be little or no mortar seam running continuously vertically down the wall. 

P.S. Extra repurposing tip - see the natty overall - we found a laundress who has a market stall, on it she sells old company overalls when they are 'past their sell-by-date'. They are really good quality and very cheap. We even once got a life-boat man's suit, which was great for heavy building work - and really good in wet weather!'

The mixing of the lime mortar and the laying of the stones and testing of the new storage heater will be dealt with in a separate blog.

Left -  another great find for our old house, this time at a yard sale, it replaced a sadly defunct Rayburn anthracite heater with a burnt-out back boiler.

The continuation of this project can be found here

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

© Andy Colley 2014

RETURN TO GREEN LEVER CONTENTS PAGE FOR MORE ARTICLES