Bricklaying notes – February 2010

1000 bricks need approx 0.6m3 bricklaying sand and 10no 20kg bags cement (when using conventional mortar)

Conventional mortar mix with lime seems to be 1:2:9 cement, lime, sand. If we just substituted our lime for the 1 cement, then we could expect a ratio of 1 lime to 3 sand, which agrees with the ratio suggested on wikipedia.

Lime putty mortars benefit from mixing with sand and then leaving covered for a few weeks, before being “knocked up” to re-plasticise them.

Lime mortar has a low compressive strength and when using it outside or exposed it is usual to add a pozzolan which reacts with the lime to make it harder. I begin to think that we might be better off using cement (modern pozzolan) and then rendering with limewash, so it can’t be seen.

Here’s a MSDS for Lime putty. It looks like lime mortar would be more corrosive than cement mortar, but you wouldn’t wan’t either to stay on your skin for long, so gloves are probably a good idea.

When using lime mortar, you need to build 1m at a time and then leave to cure for 3-5 days.

Structural Design
The single brick,  3m wide and 2.4m high wall with a return at each end is certainly strong enough to stay up as a free-standing wall.

I’m not so sure about putting the roof structure in timber on it.  It needs to hold up about 7.2m of timber plus roofing tiles.  That’s about 300kg  plus what ever wind loading I need to allow for.

Actually, I’m not sure the single brick wall is a particularly medieval building style.  There is an English and a Flemish double thickness wall style that I need to find out more about.

Structurally, I’m also more comfortable using a double brick wall, hmmm.  We may need more bricks, but there’s no hurry – we can’t build faster than 1m at a time.  I’m inclined to build to 1.2m at a time, so we only have two building weekends to do the wall.

Other stuff
I’m currently reading “Cooking and Dining in Medieval England”  and getting interested in both stoves and pastry ovens.  There’s a nifty construction that was used to concentrate the fire under the equivalent of the FOC.  And, after watching the cooking at Surveying Expedition, it looks like a dedicated copper kettle spot, with its own fire would be useful, and so would a raised area to use with charcoal and cook smaller dishes.  The Tudor kitchen at the Weald and Downland museum includes a small oven and a copper.  I only have a fire space 3m long and 75cm wide, but maybe the oven could be placed outside that.

Maybe I’m trying to do too much with this building and I should go back to my initial purpose – an inside fireplace so we can cook even when there’s a total fire ban.

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