Friday, November 9, 2012

Death of a Die

 I learned the hard way that there is a reason why dies are almost always made out of metal. I had laser cut some shapes to try out in the extruder I have been making out of PVC pipe and lumber.


 It looked so promising... I loaded up the pipe with clay and pushed in the plunger. I heard a crack but I thought that it was only an air pocket in my pug of clay.


Lesson learned. Plexiglas is too brittle to withstand the extreme force of extrusion.

Sunday, November 4, 2012

Extrusions 1


Many large-scale brickworks, Hanson included, use extrusion exclusively as the process of forming brick. I want to become more familiar with this process, which also takes advantage of the plastic properties of wet clay.

I started with a very small extruding gun, intended for polymer clay, and experimented with the force required and the behaviour of the clay. I found that extruding horizontally would create a curvature due to gravity, whose radius was proportional to the speed at which the clay was being extruded. By twisting the gun and extruding at different speeds, I created these curls.


Tuesday, October 2, 2012

Brickworks in Burlington


Arriving on foot to the Hanson Brick factory in Burlington, Ontario, Canada, the first thing I noticed was that the bricks were all the same colour on the inside, but they had an outside layer which varied from dark brown to white. My guide later explained that at this particular factory, they make 'coated' bricks, rather than 'through-the-body' bricks. The column of extruded mixture passes through a shower of sand, which has minerals in varying proportions to produce the final colour. 




I'm not sure how much I like this idea, since I am trying to find out how a material is an expression of a place. In the case of Hanson Brick, the place, the quarry, is purposely suppressed for reasons of standardization and interchangeability. They are very particular about the colour of the brick, which has to exactly match sample panels which are kept at the very end of the production line- any brick that does not have the expected shade is tossed.

The quarry is definitely the biggest I've seen so far. In order to ensure a perfectly uniform mix, they excavate the full proposed depth and extract in vertical runs down the face, rather than risk running along the line of a sedimentary bed by going horizontally.




This raw material is shale, not clay. They have the same chemical composition, but shale is a sedimentary rock. 
The shale is fed into a crusher which progressively screens and crushes it to a fine powder. There was a thick coat of light red dust on every visible surface. (See the footprints!)





The powder is emptied by conveyor belt into these large holding tanks. When the hoppers for the pugmill are mostly empty, a sensor automatically activates a second conveyor belt which feeds them. 



The powder is mixed with more water, to about 12%, before being extruded. The extruded column passes through a series of dimpled rollers intended to add a bit of variation and relief in the surface.

The extruded column, or 'slug', is then doused with sand, cut, spaced, and loaded onto 'kiln cars' which pass first through a drying kiln, which uses the waste heat of the kiln to reduce the moisture content down to 0.5%, and then through the 180m-long tunnel kiln with a specific firing profile depending on the size of the brick. The maximum temperature is normally 1065C. 



The bricks are then inspected and packed. The bricks produced at this factory are mostly for wholesale to builders, who might sign a contract for 4 million bricks per year.




Wednesday, September 5, 2012

Wall 2


One of the criteria I set for myself when designing the module was that it should create different effects according to the orientation and way of assembly. In that respect, I think it is successful; walls 1 and 2 have very diverse characteristics. Wall 2 is more static and regimented, partly because it is straight and of uniform height, but also due to the pattern of laying.







Wall 2 has less of a sense of thickness than Wall 1, but it has interesting surface effects and shadows.

The wall is two wythes thick- one wythe has 8 bricks, and the other has 7. This is so that the pattern of interference between them creates varied sizes of openings. The effect is not as noticeable up close, but from a distance, it is visible.


It is only when viewed from an oblique angle that the depth of the wall is made apparent.

Sunday, September 2, 2012

Two Handed Tooling

The mortar joints of Wall 2 are unusually complicated due to the different angles and overhangs. I found that I can get a good clean finish by having a tool in each hand: a butter knife in my left, and my favourite scraper in my right.

I start with an upstroke to trim one side, and then a downstroke to clean the other side.
Then another upstroke to clean out the gap.

I finish with a soft brush to clean up any 'crumbs' of mortar.

Thursday, August 30, 2012

Wall 1


During my first week here at Grymsdyke Farm, I was introduced to the work of Erwin Hauer. I was really captivated by the beauty of his repeating modules, especially the way light seems to bounce around within the thickness of the wall. His installations suppress any hint of materiality, but the same effect happens, for example, in Eladio Dieste's Cristo Obrero church, where it seems like the brick panels are always glowing with sunlight you never see directly. 
These two have been in my mind a lot as I have been designing my walls. I wanted to keep a sense of depth- in most brick walls, you only see one surface- a relief pattern and not a three-dimensional construction.



 One reason I like the colour of the fired clay here so much is that it really catches the sunlight well, especially in the predominantly green landscape.


Wednesday, August 29, 2012

Specials

At first I didn't want to use any module other than the main one, hoping that the unit itself would be versatile enough to accommodate every condition. I have realized that sometimes, 'specials' are necessary- the exceptions that make the system work. In my case, in order to finish an edge properly, I need some half modules. These were made simply by slicing the brick before drying.

The shape, I've realized, is interesting because it has the exact same profile on four of its sides.

Tuesday, August 28, 2012

More Mortar

After a visit and lesson from a builder, I have changed my mortaring technique and my mixture. He suggested using equal amounts cement and lime, to make the mixture even more workable, and also told me to add more parts of sand, since mortar should always be weaker than the bricks, and these bricks are pretty weak to begin with. 

I also found out that the mix I was using was way too dry, which would explain why it wasn't sticking well to the bricks. Whereas before I was working with a very hard, crumbly mortar (sort of like natural peanut butter), his mix was soft and very runny, like warm butter. (Side note: I keep finding ways in which bricks and bread are similar. In the ways that they are mixed from two main ingredients, formed, baked, and even buttered! When the kiln is firing, it even gives off a moist, dough-like aroma)


The builder shows me how to hollow out the bed so that it has somewhere to 'squish' when I put the brick down. Since the mortar is so wet when it is first applied, he suggested that I lay a whole course of bricks, then go back and clean up the joints, because by then the clay will have soaked up a lot of the water.


These are his tools- a huge trowel, a small trowel, and his personal jointing bar, which was the handle of an old milk churn.

He was 'baffled' by the shape of my bricks, so he demonstrated the proper use of the jointing bar on the field wall. Basically, it's important to compress the mortar into the joint to create a clean, weatherproof finish.

Sunday, August 26, 2012

Mortar

Mortar, like clay, is another of those neither-liquid-nor-solid substances that can take any shape- although it is best at filling gaps between things more solid than it.

The mortar I'm using is roughly 4 parts sand, 1 part cement, and 1/2 part lime. The lime, I've found, makes the mixture slightly stickier, although I still have trouble sometimes getting it to adhere to the brick. 

I've found that when it comes to mortar, more is more. It's better to overfill and then scrape off the excess, rather than to try to go back after and patch it up. Especially for the joints I'm dealing with- they are anything but regular, and have to be clean on many sides. As well, excess mortar allows me to push the brick down into place, ensuring good contact.

I am still figuring out a good technique for working, as well as trying to decide exactly how I want the joints to be finished. Bevelled? Curved? Recessed? Flush? At the moment, each brick is an experiment.



This simple frame helps me waste less mortar (although I still drop a lot!)

At the moment, my tool of choice is a flat scraper, small enough to get into the gaps between the bricks.

A generous mound of mortar...

The brick is wet- I've dipped it to try to make the mortar stick better.



I check if it is roughly level with itself and with the other bricks. 
Scraping off the excess mortar. I like the gritty 'schick' sound of the metal against the sand.


Friday, August 24, 2012

Brick Brushing

To maximize cohesion between the mortar and the brick, there are two measures I take: brushing off the sand with a wire brush, and  soaking the brick in water. 

The brushing also removes the darker sand so the orange of the clay shows through.

Thursday, August 23, 2012

The Life and Death of Formwork

Formwork is the unfortunate, essential-yet-absent material that can 'make or break' the concrete pour (or the budget, for many architectural projects!) I'm happy to say that my formwork did its job well- but sadly, it is now waste.


I chose to make the frame out of MDF, knowing that it would not be salvageable after use. The inside is thin plywood, in order to  follow the curvature.

There are, of course, different kinds of formwork that are reusable, but for a small, unique slab like this, its life ends with removal.

Tuesday, August 21, 2012

Concrete pour

After many weeks of working with clay, today I was working with concrete. It's funny, even during the most stressful times of brick-making, I never felt like I needed to be a machine- it was always distinctly human work, and the laborious tasks, such as sorting clay, also had a meditative side. Concrete is a different story. Perhaps due to the shorter working time, and the irreversible nature of the process, I was acutely aware of the limits of my body and the inefficiencies of working by hand.
Luckily I had help, in the form of Paul the gardener. 



We marched the formwork across the field. For other, heavier, things, we used the lawn tractor with the trailer. 


In order to use less concrete, we put a base layer of flint (there was lots lying around, of course). It worked well to space the wire mesh, too.


We stretched a chain of extension cords across the field in order to get the concrete mixer going. We also had very long hose, but it didn't stretch quite as far as the slab. We left the hose running for the entire afternoon, which I felt very guilty about.





Moonrise over the field after the rain.

Just as we finished, there was a downpour. 


Rain-hammered concrete: a new kind of finish?

The surface is very rough, but eventually it will be tiled over.



Saturday, August 18, 2012

Third Mold

This mold was unfortunately unsuccessful, but I did learn a thing or two about metal. Ten minutes' bike from the farm is a forge and metal workshop, and one of the techniques they use is sand casting. A full-scale pattern is packed into sand, then removed, and molten aluminum is poured into the void. 




The pattern and the cast.

I made my pattern quite thin, thinking that metal would allow for an economy of material that wood does not permit. However, when the blacksmith examined my pattern, he remarked that the cast would be liable to break, because cast aluminum is very different from sheet aluminum and can be brittle. He said that it would be better if I brought a solid block with the hole cut out- exactly like First Mold!


The blacksmith examines my pattern.

The cast did not turn out because it was hard to remove from the sand. The sand must be damp in order to hold its shape, so the pattern must be 'smooth like glass'.

Thursday, August 16, 2012

Sand Woes

Sand left in kiln after removal of bricks.

When I opened the kiln after my first firing, the bricks were...dark. Burgundy. Comparing this colour to the vibrant orange that I had seen before, I knew something was wrong. 
First, the sand I am using changes colour. It must contain a lot of iron, or some sort of clay-ish rock, because it turns from brown to burgundy when fired.
Second, I had fired the first batch to 1100C, whereas for every firing prior to that one I had only fired to 1000C. I think this changed something in the clay-sand mixture- maybe the sand melted at the higher temperature.

When I made test bricks with 50% grog, they were much stronger than just with clay. I thought that sand would work the same way, but turns out that sand makes the clay a lot weaker. The bricks from the first firing are very brittle and crumbly. I have changed the proportion of sand in my mix, so that it's now not more than 25%. I can't give up sand as a mold release, though, so I'll have to work with a different sand if I want to get that orange finish that I like so much.

But, the second firing went much better. These bricks are stronger and more orange.

Second batch brick (top) and first batch brick (bottom). I can crumble the edges of the first batch brick.

Bricks stacked after being taken out of the kiln.