Plaster of paris & flexible moulds

After seeing pro’s making sand castles and learning about the Pound-up process. I thought it would be good to use the same process to cast my concrete product. I stumbled across a picture of a guy using a vinyl sheet to build sand up vertically. I have never found that image again. And I cant find anything else on the net where they use this vinyl sheet. Although you can’t make any undercuts… I think it’s still the best way to achieve complex curves with concrete. Because it’s a liquid, you’re normally limited to the shape of your mould because of gravity. So why not turn the mould on its side and pour it in from the top. The rebar can still be placed in the centre of the mould. Once the concrete dries you can remove the mould and flip the finished product on its feet.

I had some plaster of paris and some aluminium left over from my previous models. I couldn’t help myself. I had to try it out.

This shape comes from a clay model I made a few weeks ago- the shape was modified by a skater (see skate participant #1 blog post).

Aluminium mould- mock up

clay was used to seal the bottom of the mould

Note to self…Clay will not seal the bottom of the mould! Next time use gladwrap and sitcky tape.

Pouring Plaster of paris in to the mould

Here is a clip I found on youtube that uses a flexible mould. Its interesting to see what is possible with a liquid material. Notice the foam-like flexilbe mould being used on a horizontal surface. Non-stick!

Skate Terminology

If you think I’m talking gibberish and its hard to follow me. Click the link below for a list of skateboard terminology. I’ll try to keep things as simple as possible.

Here are some general terms, tricks and equipment-

http://everything2.com/title/basic+skateboard+terminology

Next week- user participation #2

After categorising skaters’ skill levels, I still wasn’t sure how I could translate this into physical design. I needed some actual data that could help give me direction with my form design. So I’ve come up with these variables:

1. Obstacle height- Low, medium, high
2. Obstacle steepness- Shallow slope, medium slope, vertical and over-vert.  (curved transition and flat banks)
3. Speed- How fast the skater riding.

Next Tuesday I’ll be going to an indoor skate park called the ‘Ring of Fire’. I’ll get my friends to skate a series of obstacles and I will be measuring their performance. I would class them as Intermediate level skaters. They have been skating for at least 5 years now. I roughly know how high and how far a beginner can jump (Ollie) on flat ground; about 180mm high and  800mm in length moving at average speed. I’ve calculated average skating speed to be 14 km/ph or 4 meters per second. (That is 3 times average human walking speed).

• I’ll be measuring how far they can ride up a ramp.
• How steep the ramp is.
• Ill measure how far they can jump on flat ground.
• I’ll take note of how fast they need to travel to complete these tricks. What kind of assistance is needed to generate the speed?

Here are the participants- Eye on the prize

Here is the skatepark they'll be shredding- 'Ring of Fire'

Coping rails on top of a quarter pipe ramp.

This is a video showing these professional skaters building a portable ramp and putting it against a wall to skate. This is a massive amount of vert (vertical ramp section) that can only be done by extremely skilled skaters.

Here is an experienced skater doing some tricks. See the difference in size of the vert. Also notice how they have used quick-setting concrete (aka. quickcrete) to make a ramp out of a standard road barrier.