Bent Concrete Side Table


Polytek 75-60 Polyurethane Mold Rubber provided the ideal flexibility for this project. The 75-60 was stiff enough to hold our desired shape without kinking at the curves while a softer mold rubber would have bellied or sagged at the curve points.  Work quickly when mixing polyurethane mold rubber in order to avoid having the material setup before pouring.

Step 1 – Calculate Rubber Quantity

  • You want to mix up enough rubber to fill the form, but you don’t want to have excess leftover because it’s expensive. If you have a simple shape, calculating the volume will be easy, and there are many volume calculators online.
  • Break the mold down into separate shapes if it’s complex. Calculate the volumes individually, and then add them together.
  • Volume = Length x Width x Height
  • Modeling the rubber mold in a program like Sketchup. If the model is solid, you can right click “Entity Info” and it will give you the volume. With 1″ thick walls and a 1/4″ thickness on the back side, the volume of the rubber mold is 357 cubic inches.
  • The specific volume of Polytek 75-60 Polyurethane Mold Rubber is 27 cubic inches per pound. This number will vary depending on what type of rubber is used.
  • 357 / 27 = 13.2 lbs. of rubber.
  • Assuming that some rubber will be stuck to the inside of the mixing buckets, you should mix up 15 – 16 lbs. to be safe.

Step 2 – Mixing Rubber

  • Double bucket mixing: One way to ensure that you will not have any unmixed material in the final form, is to use the double-bucket mixing technique. Part A and Part B are first mixed in a 5-gallon bucket (white in the pictures of step 3 below). They are then transferred to a second 5-gallon bucket (grey in the pictures of step 4 below) for final mixing.
  • Part B of the Polytek 75 series is more fluid than part A. Weighing Part B out first will make it easier to scrape the sides of the bucket after Part A has been added. This mold took 7.5 lbs. of Part B.

Step 3 – Add Part A to Part B

  • Add 7.5 lbs. of Part A for a total of 15 lbs.
  • First Mix: Blend Part A and Part B together using the corded drill. Scrape the sides and bottom of the bucket with the spatula and continue blending for a few minutes.

Step 4 – Second Mix

  • Pour the rubber into the second 5-gallon bucket and resume blending. Scrape down the sides and bottom of the bucket just like before. Total mixing time shouldn’t be longer than 7 minutes.
  • Working Time: After the rubber is mixed, begin pouring it in the form. There’s no time for standing around or cleaning stuff!

Step 5 – Dry Gas Blanket and Cleanup

  • Spraying a dry gas blanket over the rubber will help extend the shelf-life of the material.
  • Cleaning up the rubber is actually pretty fun because it will just peel off after a few hours.
Previous: Make Mold

This project begins with a 3/4″ thick template made of melamine coated particle board which will be encased in polyurethane mold rubber to create a flexible mold.

Next: Cast Rubber Mold

Polyurethane mold rubber behaves like glue and will stick to most materials, so make sure that all surfaces are protected with Pol-Ease Mold Release.