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outdoor sculpture: momentary detour into brick

updated wed 6 may 09


Stephani Stephenson on tue 5 may 09

This question of large sculpture, leads me to think about architectural c=
lays, and the first=3D20
'layer' that comes to mind is brick and brick clay, as Vince was mentioni=
ng brick.=3D20
Generally when I think of brick , I am thinking of structures which are/=
were built of clay=3D20
rather than clad with clay. Aside from the fact that brick, in these inst=
ances is load=3D20
bearing and must have good compressive strength, the other difference, is=
that much=3D20
more clay is needed if the whole wall, rather than the outer few inches i=
s made of clay.=3D20
Clay is heavy. Brick structures, and pavements used huge amounts of clay.=
Until the=3D20
development of the steamshovel at the end of the 19th century, only shall=
ow digging of=3D20
clay deposits was possible. So cities and towns traditionally relied on =
local source for=3D20
brick clay. Local clay varies. Even clay from the same pit varies. So b=
ricks and brick=3D20
quality varied. firing and kilns varied. More on that later. Bricks are =
also made=3D20
differently, molded , pressed and extruded. different methods yield brick=
s of different=3D20
With the steam shovel, deeper deposits could be mined. The building of =
railroads and=3D20
canals allowed for more cost effective transportation and concentration o=
f brickmaking=3D20
and other architectural ceramics industry.

Note on firing:
There is not single set firing temperature for brick.
Source says brick must be fired hotter than 900 C (1652 F) to be conside=
red a durable=3D20
brick with a degree of vitrification. So that is , understandibly, the ba=
re minimum, same=3D20
as pots pretty much.
in fact , the range is given as a "Fusing temperature from 1600 F to 2700=
Just a wee bit of wiggle room, wouldn't you say?
.Building and facing brick are typically fired from 1600-2200, firebrick=

Tilemaker and brickmaker lore says that a lengthy firing improves strengt=
h. I have an=3D20
idea why, but=3D20
I would sure like to find out more definitive information about that, as =
in how long and=3D20
what degree of improvement is gained by lengthening firing cycle....) ge=
nerally , for=3D20
brick, I see mentioned 40-150 hours... but don't know what kind of mass t=
hey are talking=3D20
about and if it matters. and of course , brick firing temps can have huge=
variations,as in=3D20
clamp firing, or can be closely controlled.=3D20

Water and freeze thaw:
Water absorption in bricks is measured by the taking the average of 10 b=
ricks, though=3D20
some sources say 3. Engineering bricks are dense , strong, molded under =
high pressure=3D20
and fired carefully so they meet thresholds for strength and water absorp=
tion. Damp=3D20
proof course brick are also dense bricks with a low water absorption.=3D20
Both of these types of brick would be used for the base of freestanding =
walls or retaining=3D20
walls to prevent rising damp.
What is low in brick world? Less than 4.5% of their dry weight.

BTW This source claims there is no direct correlation to water absorption=
and durability.
Absorption below 7% usually indicates good frost resistance.
(Quote :" the destructive affect of frost is due to the 9% increase in vo=
lume that occurs=3D20
when water at 0 degrees C is converted to ice at the same temp)

One could use only more vitreous bricks for ultimate resistance to water =
and moisture,=3D20
but it would generally be cost the finest, strongest bri=
cks are used where=3D20=3D20
absolutely nothing else will do, and other grades used where they suffice=
Frost resistant quality brick are used only where the detailing cannot el=
iminate or=3D20
minimize water saturation.
SO, much of the genius in the longevity of brick buildings has to do wit=
h the skill of the=3D20
brickwork, i.e . "the detailing of the brick work is a more important fac=
tor than the brick=3D20
What is detailing?
Drainage, seepage and water movement are a consideration in construction =
and joinery.
Joints and brick are covered strategically where appropriate, (overhangs=
, gutters, etc.)
Different types of bonds are utilized (bonding is the type of arrangement=
or patterning of=3D20
the brick) ,=3D20=3D20
the bedding, the joinery...all these direct the moisture in an intentiona=
l manner,=3D20
throughout a given structure.
the mortar is also a factor . Some types of mortared joints, such as we=
athered joints,=3D20
help prevent moisture from entering, (by manually compressing the mortar=
close up to=3D20
the brick and by sloping the joint so that the lower brick lip is protect=
ed and water is=3D20
sloughed off.)=3D20
Moisture also EXITS a building via the mortar.. think of water wicking t=
hrough brick and/=3D20
or terra cotta, into the mortar then back into the air via the mortar. M=
ortar helps the=3D20
breathing of the building.
Because of this, the mortar , as opposed to the brick, tile or Arch. cer=
amics, will exhibit=3D20
damage first..
and usually only in the top 1/2 to 3/4 inch.
Repair and replacement of mortar, is relatively easy, the joints are simp=
ly repointed ,=3D20
..much much easier than replacing brick , or entire sections of brick.
Brick structures are designed for movement. Expansion joints are utilize=
d for thermal=3D20
variation as well as settling , earth movement, etc.=3D20
The source also notes that all bricks expand eventually , due to moistu=
re, though the=3D20
degree depends on the=3D20
brick..and interestingly, the most 'succeptible' is right after it comes =
out of the kiln, when=3D20
it reabsorbs atmospheric moisture. standard recommendation is not to in=
stall any brick=3D20
for first 48 hours apres kiln.
. finally
in brick world there is a "weathering index" which for any given locale i=
s the product of=3D20
the average annual number of freezing cycle days and the average annual w=
inter rainfall=3D20
in inches
if you have an index of 50-500 or over 500, you should use brick which ca=
n handle=3D20
'severe weathering' (Grade SW) on vertical or non vertical surfaces, in =
contact with earth=3D20
or not, because a brick is likely to be saturated with water and freeze, =
thus a high and=3D20
uniform degree of frost action and weathering is desireable.=3D20
if you have less than 50, Moderate Weathering (MW) is OK because the bri=
ck is not likely=3D20
to be permeated, even though it will be exposed to freezing temps, thus a=
'moderate and=3D20
somewhat non uniform resistance to frost action is acceptible. (the exept=
ion might be to=3D20
non vertical surfaces in contact with earth.)
OK in all , this I haven't even gotten to tile, architectural ceramics, o=
utdoor sculpture,=3D20
clay bodies etc.=3D20
Except to say that what will work depends on what you need.
claybody, firing temp, climate, location and positioning of work...all ma=

i guess better luck next time as I am surely near the max on this post.=3D2=

my source ofr a lot of the brick info was=3D20
"Brickwork :Architecture and Design" Andrew Plumridge and Wim Meulenkamp

Stephani Stephenson
Revival Tileworks