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

Art Nouveau Fireplace

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.

Art Deco Fireplace

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.

Old Normandie Bread OvenOld asbestos roof

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.

Strawcrete and stone storage heater - Godin stove

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. 

Strawcrete pad for a homemade storage heater

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.

Strawcrete and plain lime comparison of colour 
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. 

Chimney sweeping kit

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

Shuttering for making a DIY ecological storage heater
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. 

Cleaning stones prior to use in homemade storage heater


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. 

Stone work on homemade storage heater 

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.

Victorian cast iron fireplace

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 Colley 2014

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