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  1.  
    How difficult is it to make your own bricks?
    •  
      CommentAuthordjh
    • CommentTimeMay 6th 2018
     
    Depends what type of brick you want to make and what you want to use it for. I think moulds are pretty simple to make from timber.

    Compressed Stabilised Earth Blocks are easy to make by hand and are used for building in the developing world. A search will give you more details than you ever wanted.

    Unfired clay bricks can be made. The quality will depend on how good the clay is and your own technique. They can be used for internal, non-loadbearing partition walls and are good for thermal mass, acoustic separation and humidity regulation.

    Fired clay bricks (i.e. what is traditionally called a brick) are more complicated. First you need to make an unfired clay brick and then you need to fire it. Which involves building or buying a kiln and then fueling it. It's a lot simpler to go to the local builders merchant if you want a standard brick, IMHO.
  2.  
    Thanks @djh! I'm thinking of the traditional fired brick. Are there guides available? I'm wondering how much margin for error there I. Ie if you have the wrong type of clay, or if you fire it too cold or too hot.
  3.  
    Yes, it can go wrong! Lots of garden walls in Farnborough, Hants, where I used to live, included almost-vitrified 'rejects' - 'dribbly bricks'!
  4.  
    Posted By: ComeOnPilgrimThanks @djh! I'm thinking of the traditional fired brick. Are there guides available? I'm wondering how much margin for error there I. Ie if you have the wrong type of clay, or if you fire it too cold or too hot.

    What are you trying to achieve by making your own bricks and to what use will they be put?

    As said above it can go wrong. The kiln to fire bricks (about 800 - 1000degC.) is not easy to build and on a small scale will use a significant amount of energy to get up to temp. and maintain that temp. during the firing time. Over here DIY bricks are always sun-dried clay bricks, no one attempts to make fired bricks although some have made a home made kiln for pottery (but just small items) and lots have a bread making oven built on the principle of a kiln but usually complain about the amount of wood used to run the things (2-3 hours to get up to the 200degC needed)
  5.  
    I've been using our local clay for plastering and it's been great fun. Mind you, it may yet come back to bite me! I was wondering if it might be possible to make bricks for building, probably for a garage. A Hungarian friend sent me a video of an old guy making his own bricks. Obviously the old guy had a huge amount of experience. I'll try and post the link if I find it.
    •  
      CommentAuthordjh
    • CommentTimeMay 7th 2018
     
    The firing is the difference between bricks and plaster. Brick firing is awkward because of the number of bricks you're likely to want to make. A kiln for one or two vases is one thing; a kiln for 1000 bricks is another. Plus firing exposes any problems in your clay much more.

    I wish you the best of luck, but it's something I'd run away from personally!
    • CommentAuthortony
    • CommentTimeMay 7th 2018
     
    In the old days bricks were often made by hand on or near the site dried in a stack which then became the kiln, a fire was lit under it and kept going for a few days. The outside bricks were not so well fired and used for internal walls.

    They still make bricks like this by hand in India, I have seen them doing it.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 7th 2018
     
    My 1790 Georgian terrace house in Bath (back when they came at startahome prices) had internal walls made of 'Great Bricks' i.e. 12" x 6" x 4", which were crumbling to sand, except for the core of each brick, about the middle half of it, which was an egg-shaped lump as hard as flint! Talk about firing problems.
    •  
      CommentAuthordjh
    • CommentTimeMay 7th 2018
     
    fostertom wrote: "My 1790 Georgian terrace house in Bath (back when they came at startahome prices) had internal walls made of 'Great Bricks' i.e. 12" x 6" x 4", which were crumbling to sand, except for the core of each brick, about the middle half of it, which was an egg-shaped lump as hard as flint! Talk about firing problems."

    That doesn't sound like a firing problem; it sounds like poor raw materials to me. Clay doesn't turn into sand.

    I was interested by Tony's comment to find out when the 'old days' were and it seems it was about two hundred years ago. There's an interesting description at http://heritagecrafts.org.uk/brick-making/ that might give an indication of how difficult or easy the job is.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 7th 2018
     
    Well not sand, but you could scratch it away with your finger
  6.  
    @djh, that's a great link. It includes details about this amazing guy: http://ajmugridge.co.uk
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 8th 2018
     
    • CommentAuthordickster
    • CommentTimeMay 9th 2018
     
    Well what a coincidence!

    As part of my "make an iron knife using only locally sourced materials from scratch" project/hobby/jobs around the house avoidance scheme.....I need clay pots, especially one for treating a deer skin (yet to be found) in a solution of lye in order to make bellows for smelting iron ore.

    In order to fire pots I decided to make a kiln from bricks, rather than a single use clay walled jobby that would deteriorate through wet and frost. I can move bricks into shelter when not in use.

    I'm about 20 bricks in of the 120 I need, using 1:2 clay to sand mix. 2 litres of clay to 4 litres of sand = 7 bricks, painfully slow. I plan to fire these in an roughly shaped ironstone kiln for starters. The ironstone will soften and deteriorate during use, so it's a bit of a tricky unknown.

    I have biscuit fired a couple or so test bricks elsewhere. They hold together well and are dull and stable, rather than
    highly fired and brittle, so should be good to go.

    The above possibly doesn't help much, but you never know!


    .
  7.  
    There's a sculpture group over the road from me who have their own kiln. I'm going to ask them if they wouldn't mind baking a brick for me from our clay when they next fire it up.
  8.  
    What temperature does a brick need to get to when being fired?
    •  
      CommentAuthordjh
    • CommentTime6 days ago edited
     
    Posted By: ComeOnPilgrimWhat temperature does a brick need to get to when being fired?

    From the link I posted:

    "The firing usually takes two to three days (including the nights continuous firing and reach a temperature of around 1,040 degrees Centigrade."

    Alternatively, bricks are just earthenware so according to https://en.wikipedia.org/wiki/Earthenware

    "Modern earthenware may be biscuit (or "bisque") fired to temperatures between 1,000 to 1,150 °C (1,830 to 2,100 °F) and glost-fired (or "glaze-fired") to between 950 to 1,050 °C (1,740 to 1,920 °F), the usual practice in factories and some studio potteries."

    edit: The length of time is because of how thick the clay is in bricks. Most pots, including sculpture, are hollow, with thin walls, so take less time to fire.
    •  
      CommentAuthorfostertom
    • CommentTime6 days ago edited
     
    Posted By: djhThe length of time is because of how thick the clay is in bricks. Most pots, including sculpture, are hollow, with thin walls, so take less time to fire.
    Really? It can't take a fraction of that much time to overcome thermal resistance + thermal capacity and achieve uniform temp throughout such a thickness.
    • CommentAuthordickster
    • CommentTime6 days ago
     
    I think length of time is more to do with avoiding thermal shock on the way up and on the way down. Heat too rapidly and the outer and inner parts of thick clay (brick) expand and contract at different rates= cracked pot or brick. Ditto cooling down, outer skin of ceramic cooled by wind, let's say, inner still red hot =cracked pots/bricks.

    Plus at two critical temperatures, clay forms crystal structures thus all of the ceramic needs to be at the same temperature at the same time at these temps to avoid yet more cracks.

    So longer and slower the thicker the clay.

    Interestingly major modern ceramic manufacturers using computer controlled heat have reduced firing times from days to hours now that a more complete understanding of what's happening in the kiln has become known.

    There is still a lot of witchcraft around to play with though.
    •  
      CommentAuthorfostertom
    • CommentTime6 days ago
     
    Makes more sense.
  9.  
    Posted By: dickster
    Interestingly major modern ceramic manufacturers using computer controlled heat have reduced firing times from days to hours now that a more complete understanding of what's happening in the kiln has become known.

    Based on a bit of hobby firing of porcelain clay, many years ago...
    IIRC, a classic firing had 3 main phases, a long slow ramp up of temp, a 'soak' at the top temp, then a long slow cool down. As you mention, a significant factor in the the slow ramp up & down was to avoid thermal shock and ensure even heat distribution.

    Posted By: dickster
    There is still a lot of witchcraft around to play with though.

    In the 'old days' the state of the fire was assessed using 'cones'. A 'cone' was a small piece of ceramic material of known properties, shaped like a tall pyramid with an off-square base so that there was a lean to one side. You chose the cone number to suit the type of material you were firing and the nature of the fire. The cone was placed in the furnace so that it could be viewed from a (plugable) hole. When the cone started to deform to a certain degree that indicated that the heat could be turned off.
    When we started our hobby firing that had developed into a 'kiln sitter' in which the cone was a small prism (or toblerone!) shaped bar of ceramic material placed across two supports with one end of a trip level resting on the middle of the bar. As the cone started to deform, the lever moved and tripped the power switch.
    Later we got a proper thermocouple and were able to monitor & control the process more precisely.
    Even at the hobby end of the market, multi-stage programmable controllers were just coming into play when moved on to other things.
    •  
      CommentAuthordjh
    • CommentTime6 days ago
     
    Posted By: fostertomMakes more sense.

    Makes more sense than what, Tom? Than what you said? Because what I said is correct. Dickster agrees. I don't think his reasons are complete though. The length of time for various chemical species to separate from and migrate through the clay is also important at various times and is typically the most important factor, alongside the simultaneous changes to the crystal structure he mentions.
  10.  
    Presumably shrinkage is a bit of a problem. At least from wet to dry, our clay shrinks quite a bit. I could add aggregate as we do with the plaster, but might this be a problem? Does it need to be pure clay?
    •  
      CommentAuthorfostertom
    • CommentTime6 days ago edited
     
    Posted By: djhMakes more sense than what, Tom? Than what you said? Because what I said is correct
    I shoulda said what djh said now makes more sense, the more detail is added.
    • CommentAuthorowlman
    • CommentTime6 days ago
     
    When I built my home I salvaged a thousand+ old clamp bricks from some on site derelict buildings. I cleaned them and incorporated them into the interior, namely a large thick wall which separates two distinct areas of the house. Many of the bricks were mis-shapen with great bulges, where presumably other matter had been mixed with the clay and caused the clay to "blow" when fired.
    I used them nevertheless and now 30+ years on I still wonder if I did the right thing. The rough nature of this characterful wall attracts dust and needs vacuuming occasionally but visitors usually love it for that character look.
  11.  
    Posted By: ComeOnPilgrimPresumably shrinkage is a bit of a problem.

    It certainly happens with porcelain. A properly fired (i.e. vitrified) porcelain piece is distinctly smaller than the model it was created from. That can be used to make a size series of a single design from a single original model (sculpt the original, make a mould, cast, fire, make a mould from the fired head, cast, fire, make a mould from the fired head,...)
    You can loose detail along the way (but some can be regained by working on the mould, or on the greenware[1]).


    [1] Greenware = After casting, before the first[2] firing.
    [2] With pottery there are often 2 firings. First a lower temp firing to 'bisque' (biscuit ware) - think of teracotta pots.. Depending on the type of clay & other choices the bisque might then be coated in glaze then fired again, or (e.g. porcelain) fired a second time to a very hot temperature to vitrify the clay.
  12.  
    Thanks @skywright. In that case, presumably it's fine to use pure clay. As the shrinking takes place in the kiln rather than the house, I guess you just need to work out how much shrinkage takes place.
    • CommentAuthormuddy
    • CommentTime3 days ago
     
    Great idea to make your own bricks, we're on clay here. Look at an OS map for sites of old brickworks in your area.
    The shrinkage will be about 12per cent, depending how soft the clay, and softer clay is easier to mix unless you have a pugmill. Shrinks on drying, and in the kiln. The more vitrified, the greater the shrinkage in the kiln.
    It's a good idea to cut frogs into the brick to allow it to dry quicker. If you heat the brick too quickly in the kiln the steam can't escape fast enough and explodes. Above 500 centigrade you can turn up the kiln to max.
    Why not use the same materials and make cob bricks, unfired.
    Brick making technology is quite refined to minimise waste and maximise profit.
  13.  
    Thanks @muddy. I was thinking about frogs as some of the engineering bricks we have have frogs in them. you can even see the mark where the screw held the piece of wood for the mould in place.

    How deep do you think the frogs should be?
  14.  
    I have seen bricks with no frogs (I had a house with these, built with lime mortar, a nightmare to put in a fixing as when the drill hit the brick it disappeared into the cavity!) and bricks with about 60% of depth as the frog although I thought that the main reason for such a deep frog was to reduce both raw material for the brick and reduce transport costs (weight). Bricks with very deep frogs use a prodigious amount of mortar.

    So as far as I am concerned you pays your money and takes your choice.

    You could always go to the builders merchant and see what the typical brick has - around 5cm I would guess
   
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