Casting Test

I tested casting 8 panels using different techniques.

  • Concrete mixed with black chalk with blue added by tube
  • Concrete poured over black chalk
  • Concrete mixed with blue chalk
  • Concrete poured over blue chalk
  • Concrete poured around tubes filled with blue chalk, tubes removed after pour
  • Concrete poured over black and blue
  • Concrete poured with remaining chalk pressed in and “marbled”
  • Concrete mixed with metal shavings, poured over metal shavings


  1. Prepare work area by laying down paper or plastic sheeting
  2. Construct molds and coat with vaseline
  3. Mix Quickrete with water in large bucket
  4. Transfer to smaller bucket for specific test mixing
  5. Pour into mold and vibrate until mold is evenly filled
    2014-03-25 19.12.55
  6. After a few hours of hardening, remove from molds carefully and set out to cure completely.  In this test, the cardboard molds absorbed and retained moisture.  This caused the curing to happen more slowly.  When I removed the molds, the concrete was still soft and I was able to break off chunks at the corners where the cardboard flap interrupted the pour.
    2014-03-26 00.52.40
  7. The next step is to wash the cast pieces with soap and water  This removes excess chalk and Vaseline and will allow closer inspection of the casts.  I rubbed soap into the tiles with my hands and rinsed several times.  The bulk of the chalk washed off but some remained on the surface.  Deeper scrubbing with a stiff brush could remove more.  In places where chalk was not mixed in thoroughly (such as where it was pressed in), the chalk washed out completely leaving voids in the concrete and exposing some of the concrete aggregate.  I could not thoroughly wash the tile with the metal fragments with my hands without harming myself.
  8. 2014-03-26 12.40.17Brush tiles with soap and water using a stiff brush.
  9. Break tiles and observe cross section.

Observation on Pour Consistency

It took a significantly longer amount of time to fully harden.  This is because I mixed in too much water.  This also likely compromised some of the strength of the casts.  Later casts had a lower water content.  Each cast was unique in its concrete consistency.  This is because I mixed the concrete with a stick and not with a shovel.

Observation on Mold Quality

The cardboard boxes I cast into absorbed water and deformed.  The side walls of the boxes bowed outwards, changing the shape of the cast.  The surface of the cardboard warped which left an impression on the casts.  While the casts were trying, I pushed them all together so that they would support each other.

The Vaseline I used as a mold release was effective.  In casts with a higher water content, the texture of the spread Vaseline left an impression.

Observation of Metal Content and Weathering

See my post about accelerated weathering.

Observation on Chalk Mixing

Mixing chalk into the aggregate works well to color the cast a specific color.


The white streaks were caused by the vaseline mold release. The bottom surface [right] is warped from the cardboard mold becoming waterlogged.


The underside is a homogeneous blue but the exposed surface [left] shows the blue chalk subtly highlighting the structure of the aggregate.

Observation on Chalk Infusion

For this first “chalk infusion” I filled tubing with the chalk dust  and poured the concrete over the tubing.  I then removed the tubing leaving the chalk in place within the cast.  The effects are…blah.


You can see that the mold became weakened on one side and the weight of the concrete pushed it outward.

For the next chalk infusion I used a flat piece of wood to press chalk all the way through the concrete to create a “seam” of chalk.  When I washed the panel, the seam dissolved in the water leaving a pitted concrete surface that exposes the cement-aggregate structure.


Observation of Pouring over Chalk

For these ones I covered the bottom of the cast with chalk and poured over it.  When I rinsed the panels, much of the chalk washed away.  Further brushing of the panel would leave chalk only in the deepest parts of the surface, possibly highlighting the texture of the aggregate.