Saturday, May 28, 2011

How to Make a Concrete Butterfly: Part 2

The materials:

Like the materials list in Part 1, what you'll need for the second part is very simple and inexpensive: A cup of water, rubber gloves, sand and Portland cement. Optional is the Quikrete acrylic fortifier shown here. It improves the water resistance of the mortar, but plain water works too.

I mix my own mortar. If you wanted to buy pre-mixed, you would want a mortar mix, not a concrete mix. Concrete mix uses gravel aggregate which would be too lumpy for this technique.  You can also screen your sand and cement prior to mixing to get a really smooth finish.

My recipe for the mortar is:

1 part Portland cement
3 parts sand
1 part water (approx)
(or optionally, 1/2 part water, 1/2 part acrylic fortifier)

In the case of this butterfly, the "part" I'm using is a small pudding cup (shown).  For small projects like this, I do all my mixing by hand. It allows me to work out lumps and small rocks, and is simply easier than using a tool. Be sure to wear gloves, however, as the concrete is very hard on your hands.

Mix the sand and cement thoroughly before adding any liquid.  When you do add liquid, add it in small batches, working it in thoroughly before adding more.

Add liquid and knead until you've worked it into a sugar cookie dough consistency, shown below:

This may still be a bit dry as you work with it, but I prefer to have it on the dry side.  As I'm working the mortar into my wire armature, I dip my fingers in the water to add wetness as needed.

Work the mortar onto the body first.  When mortaring the body, you want to work the mortar into the armature to fill the center.  You want the mortar to go through the body and adhere to the rebar and antennae wires so that it is all solid when dried.

I've found that putting the rebar into a bucket of sand helps tremendously.  This allows you to move it around and position it where you need it at the moment.  Keep in mind that you'll be working the top and underside of this butterfly.  The sand helps hold the piece in place while you do that.  This particular bucket of sand is mixed with WD-40 because I use it to clean my garden tools.

Once the center is filled and shaped, shape pieces of mortar into patties and press them onto the wings.

Keep taking small handfulls of mortar and press them onto the wings, being careful not to let the mortar slip all the way through the armature.  Alternately, I dip my fingers in water to moisten the mortar and help shape it as I go.

Keep patting the concrete onto the wings until you've got them shaped and almost fully covered.  If you intend to apply a surface treatment, like mosaic, it's okay to have some of the wire armature exposed on the edges.  You can cut that off after the mortar has cured.

That being the case, you can also leave some of the wire exposed on the underside of the wings since it will end up covered with thinset and tile.  However, if you plan to paint the butterfly instead, you'll want to finish the underside of the wings the same as you finish the top, making sure all the wire is fully covered.

When done, I mist the entire piece with water then cover with a plastic bag.

Keep covered and moist for at least two days. This prevents the mortar from curing too fast and cracking.

Once cured, I scrub the rebar clean then spray the rebar stake with Rustoleum spray paint.  This seals the rebar to prevent it from rusting, and gives it a nice finish.  For these, I chose a silver finish.

At this point, you can finish the butterfly however you'd like.  It could be painted or stained, or in my case, I'll be covering it with mosaic.  They should be weather resistant in any climate.