HOW TO MAKE
from TEMPLATES and "SWEEPS"
One way to make concrete birdbaths,
concrete bonsai planters, concrete pots and
The finished birdbath
This technique shows a simple and
inexpensive way to form concrete for any type of item that has both
an inside shape and an outside shape. For
instance, a birdbath has a bowl shape on the
inside, and another curved shape on the
Other items that can be made by
"sweeps" are things like planters, water
dishes, dog bowls, bonsai pots, saucers, and
so on. All these items could be made by using
molds, but they would require two-part molds,
plus a backup mold to hold everything together
while the mold was used. And if you only
wanted one item, it would be a very expensive
way to produce the item.
The basic idea is to rotate a
template for the inside shape around some
material like clay. This forms a clay bowl,
upside down. Then a template to form the
outside shape is rotated around the clay, but
this time with concrete between the clay and
the template. After the concrete sets and the
clay is removed, you have your concrete item.
All the steps are demonstrated with
photos and described below. The item
demonstrated is quite a large birdbath, 24"
across, 3" deep in the center, and weighing
about 50 pounds. We will be showing some
custom steps that we did to make this
particular birdbath, but that you do NOT need
to do for most items. For your first attempt
with this technique, it would be much better
to try something like a 16" wide, 2" deep
birdbath, or a small bonsai pot.
- Portland Cement.
- sand (builder's sand, mason's sand,
play sand, "all purpose" sand, etc.) Most
"play sand" is easier to use for this
technique because it usually has fewer
pebbles. Other types of sand may have a lot
of pebbles that make working with the
concrete more difficult.
- water base or oil base clay.
- scrap lumber such as 1x4 or 3/4"
- 1/4" metal rod.
- cement trowel or mason's trowel
(steel trowels are much better than plastic)
- mixing bucket or mortar tub
- stiff plastic sheet or tar paper or
- powdered concrete pigment if you
want any color besides "concrete gray"
- graph paper to make a template, or
use a computer CAD printout if you want
- any kind of tool that can cut
curves in wood - coping saw, scroll saw, jig
saw, band saw, etc.
- a drill or drill press, with 1/4"
- hot melt glue gun
The first thing to do is make a paper
template that represents a cross section of
one half of the item. The template for the
large birdbath is shown below. Concrete needs
to be at least 3/4" thick for strength, so
your template should be at least 3/4" wide at
all points. Our template is up to 1-1/4" wide
in some spots because the finished birdbath
will be so wide, deep, and heavy, and the
sides will not be supported by the ground. If
you make a 16" wide x 2" deep birdbath then
3/4" is plenty.
The paper template
Now trace the outline of the inside
onto a piece of 3/4" thick wood or plywood.
You want to allow an extra couple inches of
length in the area marked "A" so that the
metal rod that will act as a pivot has a place
to pass through the wood template. Later
pictures of the template in use show where the
pivot will be.
Your template does not need to be all
wood if you have other materials available.
You could make the main arm from wood and the
template that forms the actual shape from
thick plastic or sheet metal for instance.
In our template, we have added a
"leg" that will rest on the forming base
because we are going to attempt to make a
curved edge on our birdbath. For your first
project, you do not need a leg. The clay and
concrete will be formed directly against the
base, and make a flat edge instead of a curve.
The inside shape is traced
You need a flat work surface covered
in a waterproof material, larger than the item
you are making. A piece of flat stiff plastic
is good, or you could use tarpaper. Thin
plastic such as garbage bags is not a good
material - it will bunch up and get in your
way as you rotate the templates.
Your work space should be outdoors
but protected from rain, and a space that you
do not need for a week or so. A carport floor
or garage floor would be ideal. For concrete
to cure properly, the temperatures must stay
over freezing. Temperatures over 60 degrees F
would be preferable.
Next you need a 1/4" metal rod that
will act as a pivot, stuck vertically into a
1/4" hole in a block of wood. Take pains to
make sure the pivot rod is vertical. Any
leaning in the pivot rod results in your
template rubbing on one side and missing
completely on the other side as you rotate it.
Drilling the hole in the block of wood with a
drill press is a good idea if you have one.
Do not permanently fasten the pivot
rod into the block of wood. You will need to
pull the pivot rod out of wet concrete at the
very end of the project, and you will not be
able to get to any sort of fastener that is in
the block of wood. In other words, the pivot
rod should fit into the block of wood firmly,
but not so firmly that you cannot pull it out.
The pivot rod in a block
If you are making a large or deep
item, you can add something to take up space
at this point. That will decrease the amount
of clay you need to use. For our large
birdbath project, we happened to have an old
broken plastic saucer, and the saucer was
smaller than the inside of our new birdbath,
so we used that to take up space.
First we hot melt glued the wood
pivot block to the center of our plastic base,
then we drilled a hole in the exact center of
the saucer and pushed it over the pivot, and
hot melt glued the saucer to the base as well,
so the pivot is fixed in place. Gluing the
block of wood to the base makes it stay put
when you need to pull the pivot rod out of it
through the wet concrete later.
The saucer that just takes
up space, over the pivot
Now you need a spacer that fits on
the pivot rod, and holds the template at the
right height. If you make a lot of things by
sweeps, it is handy to get some 1/4" "shaft
collars" such as those shown below. They fit
over the pivot rod and can be tightened in
place at any height by using a set screw. The
home centers usually have this item in their
specialty hardware section, usually in a
If you are making your first project,
you can just use a piece of wood of the right
thickness, with a 1/4" hole so it fits over
the pivot rod.
Two shaft collars and an
Now you need to cut the template
shape out of the wood, and drill a vertical
hole through it so it will fit on the pivot
rod and be able to rotate around the pivot.
Put a shaft collar or wooden spacer
on the pivot rod, under the template, so that
the template has something to "ride on" as you
rotate it. Position the spacer so that the
template will be level. This will ensure a
level bottom to your project, if your template
has a flat bottom.
If you are using shaft collars, you
can put one above the template also. This will
help keep the template from riding up as you
form the clay or concrete.
The distance marked "A" on the
template is the inside radius of our finished
birdbath. You can see that the template needed
to be a little longer where the pivot goes, so
the pivot had some material to go through.
The area marked "B" on the template
is where we will attempt to make a curved edge
on the birdbath. Your first project does not
need this, and it does not need the "leg" that
holds the template off the base either.
The template for the
inside shape of the birdbath in
place on the pivot rod
Now you need the material that you
will form to make the inside shape of the
item. If you already have enough soft oil base
clay, that is an excellent material. If
you don't already have some it will add a lot
of expense to the project.
For our project, we used some clay
that we dug out of our garden. If your part of
the country is also "blessed" with heavy clay
below the topsoil, then you also have a free
source of material. This type of clay can
crack and split when it dries out, so you can
make a mix of about 50:50 sand and clay to
prevent that, but which is still very
Plaster is not really a good material
to use because you would need to break it out
of the inside of the birdbath or planter when
you are finished, and that risks cracking the
Damp sand alone will be difficult to
work with. Even though you can make a perfect
shape with it, it will want to move around
when it comes time to sweep the concrete over
it. You could try forming it and then spraying
it with white glue mixed in water so that it
stiffens the outer layer, or you could try
adding a thin layer of plaster over it to make
a hard shell.
Clods of garden clay
If you use clay from your garden, it
will be easier to mix with sand and wet with
water if it is broken up.
After breaking and sifting
A heavy-duty 1/2" drill motor and any
type of mixing blade will make mixing the
clay, and later the concrete, easier. But you
can do both by hand with a trowel or similar
tool if you need to.
In the picture below, the mixing
blade on the left is sold for mixing sheetrock
"mud" or tile grout, and works very well, but
you need a large and powerful drill motor. The
other two mixers are sold for mixing paint and
take a little longer to get results, but your
drill motor does not need to be as large.
Types of drill mixers you
can use for clay or concrete
Now you can add your clay. At first,
you do not need to use the template to form
the clay, but you can use the template so you
can tell when you have enough clay. Then you
can sweep the final layer of clay to make the
clay take on the shape of the template.
Most of the clay is added
without using the template
The template makes the
final shape in the clay
For our particular project, we found
that the wet clay would not hold the shape of
the rounded edge like we wanted. So we raised
our template slightly by putting a washer on
top of the lower shaft collar, and added about
a 1/8" layer of plaster to make a shell.
We found that the template would
still not make a nice rounded edge, so we made
a form from plastic strips, added more plaster
around the edge, and customized the sweep to
form just the rounded edge by using an old
measuring spoon as shown.
You do not need to do any of this. We
just show it here to explain the white
interior form you will be seeing after this
The customized template to
form a rounded edge
Now you should have the interior
shape all swept out, and it is time to make
the template that will form the concrete. Do
this by tracing the outside of your paper
template onto wood, and cutting out the curve,
allowing some space for the pivot rod as
before. Drill the hole for the pivot, add
spacers below the template to keep it the
correct distance away from the interior form,
and make sure the template is level.
It is not obvious in the picture, but
we used two threaded rod coupling nuts under
the template to keep it the correct distance
from the interior form. You could use a wood
spacer or a stack of large nuts or washers to
do the same thing. You want to use a spacer
that you can pull out of wet concrete. The
shaft collars we used previously lock on to
the pivot rod so they would not be a good
The piece of wood we used for the
template was not wide enough, so we attached a
wooden paint mixer stick to the outer edge of
the template, so that the stick rode on the
base and made the template level as we rotated
If your interior form is clay or
clay/sand, you do not need any release agent.
If you use a plaster shell you should coat it
with motor oil or petroleum jelly to keep the
concrete from sticking.
The template that will
form the concrete
Now you are ready to form the
concrete. The concrete mix you need is:
- 3 parts sand
- 1 part Portland Cement
- liquid or powered concrete color
if you wish. Follow directions that come
with it for the amount.
- the least amount of water you can
use and still mix the concrete thoroughly
Mix the sand and cement first, then
add water very slowly until the concrete is
just wet enough to mix. You do not want the
mix to be soupy or have any excess water. You
cannot sweep soupy concrete. The concrete must
be rather stiff.
You also cannot sweep anything sold
as "concrete mix" because it has gravel in it.
You must make your own concrete mix as
described, and it is best if you use "play
sand" or another fine sand that does not have
a lot of little pebbles in it.
As with the clay, you can add
concrete using a trowel until you have enough
to start being affected by the sweep, then
start using the sweep and make the final
shape. A trowel also comes in handy for some
final smoothing after the shape is made with
the template. A wood template like this leaves
a rough surface in concrete.
For our particular project we wanted
to add some reinforcement since the birdbath
was going to be quite large and the sides
would not get any support from the ground. We
put about a 1/2" layer of concrete over the
interior form, then used some poultry cloth
for reinforcement, and then swept the outer
layer of concrete over that, so the wire was
completely embedded in the concrete.
For smaller projects, you do not need
to use any reinforcement as long as the
concrete thickness is at least 3/4".
Concrete being formed
after adding some poultry wire
After the concrete is completely
swept and you have your finished shape, the
pivot rod and any spacers need to be pulled
out of the concrete. This will leave a hole
that you can patch by forcing concrete mix
down into it and smoothing it off with a
For our particular project, we did
not add color to the concrete mix. We had some
colored sand though, and pressed it into the
wet concrete, after the concrete had stiffened
up for a couple hours. (Technically, it was
3M™ Colorquartz™ Ceramic-Coated Crystals) If
you add something like colored sand too soon,
it will just sink into the concrete and be
invisible. If you try to add it too late, it
won't go in at all.
When you are finished with the
concrete, cover your project with a plastic
garbage bag, weighted down around the edges.
Let the concrete cure undisturbed for one week
to allow it to attain maximum strength. You
can check on the concrete every couple of
days, and if any part of it seems to be drying
out, spray or pour water on it and replace the
plastic. Concrete needs to stay damp in order
to cure properly.
Colored sand added to
outside of concrete after it has
stiffened a bit
You can see the finished colored sand
effect in the picture at the top of this page
- a pleasing sort of "granite" look, not
nearly as garish as the above photo would
You can also see the slightly rounded
edge we worked so hard to get.... Probably not
worth the time and effort.