Imagine a media that is inexpensive, easily carved, environmentally safe, attractive even in its raw form, light weight,
submits itself to carving; while its surface can be finished in a variety of fashions. These enticing attributes all
belong to Autoclaved Aerated Cement (AAC).
It is a dream to build with, as it carries loads up to 1,200 PSI, it has a high fire resistance and has a high
insulating factor. It rates high as a sound barrier and it also is comparatively light weight, being 80 % air,
all the while an environmentally friendly material. The formula includes either a fine sand or fly ash, a
byproduct of coal burning plants, so the creation of it can be of benefit to the environment as well.
A block of 18" X 24" X 12" weighs about 50 pounds.
Aluminum is added to liquid cement causing a chemical reaction that produces tiny air pockets persuading the
material to rise like dough. After drying, the aerated cement is then placed in an autoclave and baked at 375
degrees Fahrenheit for half a day. Under the autoclave's pressurized steam, a chemical crystallization takes
place, adding further strength to it. The result is an air filled cement that can be sculpted, cut, carved,
drilled, chiseled and sawed with conventional sculpting and carpentry tools, both by hand and power tool.
AAC is a subtractive material only, meaning that just like stone, nothing like itself can be added to it.
An electric saws-all is most useful in general shaping and forming. Some of my favorite hand tools are
rasps, metal hand sculpting tools, large and medium wood draw knives and some metal pottery draws. I
have used dental tools to finish some fine detail. AAC can even be sanded with paper, demanding a sensual finish.
Although created for the construction industry, AAC is perhaps even more ideal as a sculpting media.
Yet there are only a few artists who have discovered it! Even though the artistic use of the material
is in its infancy, AAC outperforms so many other well known and widely used alternatives. Sculpting
in this new material can bring you to creative places you could not find without embracing it. The
ease of its use allows the artistic vision to form comparatively quickly.
Being discovered in the 1920's in Sweden, AAC has been used in Europe for construction ever since.
It is taking us here in the US a bit longer to wake up to its advantages, though over the last 10
years the word is getting out, especially as green building becomes more in demand. AAC is made
domestically in; Georgia, Florida and Arizona. You can locate the information nearest you by
simply searching for it on the web. For those of you that do not live by a manufacturing plant,
there are a few distributors out there that may make it a little easier to come by. Remember that
these are people that are used to selling in bulk to the construction industry and they may not be
willing to sell you in small orders, though you may find some that are sympathetic to the artists
plight. If you are in the Portland, Oregon area, I personally have smaller quantities available.
Since AAC is baked first and then cut into pieces, the material can be purchased in various sizes,
though they are more readily available in construction sized slabs and various blocks and bricks.
Because it is formed in sections that are 20 feet long, much longer and wider pieces are offered
from some companies, though you may be required to make large purchases to order specialty sizes.
Handling and transporting is the only limitations beyond its manufactured size, 20' X 4' X 4',
usually. Don't forget to figure in the shipping costs because that can actually end up to be more
expensive than the blocks themselves depending upon your location. Remember, you will be shipping
cement, even if it is light weight cement.
Bonding blocks together is an alternative to the cost and the difficulty of handling and transporting
larger pieces. The best bonding agent I have found is the one that is made specifically for joining
AAC blocks, E-crete. Resulting in joints that are stronger than the material itself, E-crete
offers a union with no fear of splitting or cracking. If you are finishing your piece with a
surface cover, the lines can be made invisible. Another alternative is to make the lines
purposely visible, as Rick Gregg has done in his sculpture pictured in this article.
There is quite a bit of dust that is airborne while working with the material, especially
if you are using power tools. In consulting with an AAC manufacturing company, I was assured
that a mask was not necessary unless "One stood in clouds of it, for years". I recommend
erring on the side of caution and wearing a mask when there is excessive dust, as particles
of any kind can be irritating to the lungs. One way I have discovered to reduce the dust
level is to wet the material. I actually keep a bucket right next to my sculpture and pour
water over it fairly often. If it is a relatively small piece, you can even immerse it in
water, letting it absorb as much as possible before and throughout sculpting. The result
is little airborne dust to speak of.
AAC can be left to the elements in its natural form, to weather with the sand and sun in
the southern states or grow mold in the wetter climates of the Pacific Northwest. The
mold can even be cultivated as part of the piece with a recipe of buttermilk and mold
mixed together in a blender and painted on. The result is an encouragement of the mold,
creating an ancient looking effect. If weathering in a dryer climate with wind blown sand,
it will wear away at a rate faster than stone, which could be an interesting aspect of the
piece. There are also finishes that can be added that would ensure that the elements would
not easily contribute to or alter the art as mentioned above. It is all dependant on the
vision of the particular artist and direction she/he wishes to travel in.
AAC can be easily damaged if it is left in its 'raw' sculpted state. There are as many
different finishing options available as you can think of. A covering of regular cement
can be done, I personally prefer white cement as it lends itself to dyes more easily.
The most effective method of creating a strong hard surface out of liquid is to make a
slurry of cement and water, dipping the sculpture in and reworking the details again and
again. Other simple surface protectors or coverings are polyurethane spray and paint.
I like the effect also of a cement dye directly placed on the finished piece with final
layers of polyurethane. The effects can be as diverse as pottery glazes. Some fellow
sculptors and I are playing with a paper/polyurethane finish that has been developed by
Dennis Stewart, a fine art paper sculptor.
All of the more conventional cement enhancers and treatments can be used on AAC with
varying results. As with anything else, it depends on the effect you want as to what
materials are appropriate for incorporation into your work. Cement dyes can be either
added to the surface coating mixture, dipped into the dye liquid or painted on.
Sealers, glues, etc. all have a predictable effect, although I have found that
the commonly available cement sealers and glues are not as effective as are the
ones that are made with ACC in mind specifically. Acid stains can be used as well
on the bare surface block. It can be quite lovely with a surface coat of powdered
Readily responding to gentle urgings from my sculpting tools, this media lends itself
to my art so freely. In pursuing it, the vision in my head is allowed to form itself
in response, more completely than any other media I have worked with. When my students
are introduced to it for the first time they are quite pleased with the results of their
efforts. The material offers its rewards for the expert as well as the beginner.
Fifteen years ago, I began sculpting out of clay and moved to wax having my final pieces
cast in bronze. I then shifted to casting in glass only to find myself drawn to what
could be done in cement. The limitations of having to do most of my sculpting in the
semi-liquid form, kept me searching for a material that would offer more solid versatility.
As with any medium, I am not sure I would have traveled to where I am in the creative
process without engaging with AAC. My work is leaning at this point towards sensual
organic forms, this material has assisted me in traveling far from the genre I began
with. At the very least, it has made my journey here more straightforward. I look
forward to seeing what is possible for others and the directions they travel to.
Other names Autoclaved Aerated Cement, (AAC) is known by; autoclaved cellular
concrete, autoclaved aerated concrete, airstone, greencrete, grancrete and aerblock.
These sites have pretty good lists of manufacturers of AAC, they would also have
access or knowledge of E-crete.
If you are in the Portland, OR area, you can buy small quantities through Carole.
The author's website, including more AAC sculptures - www.CaroleMurphy.com
Rick Gregg's website - www.RickGreggStudio.com