Applying Rubber Sole over Existing Leather Sole
During our Kickstarter campaign, a lot of our customers have requested to put rubber outer sole on top of the leather sole. This helps in increasing shoes’ durability, especially for use in wet weather.
Putting rubber outer sole on top of leather sole was new for our artisans. The idea was, therefore, not well-received at first. It took them some time to digest it. After convincing them that it is what our customers want and will make them happier, we sat down with a few subject matter experts and started devising a way for it. It was clear to begin with that we needed to acquire rubber which must be soft and a bit rough on one side so it can grip better when pasted over leather.
The next day, I hit the road to Shah Alam market in Lahore which is considered the biggest market for raw materials in Pakistan. We needed a rubber which was neither that cheap nor too costly and at the same time had the right thickness and the right kind of softness to hold onto the glue. I bought three different kinds of rubber sheets with varying softness and thickness. The idea was to prepare different samples out of them. We did around six samplings, applying different kinds of rubber soles with different widths onto different kinds of leather outer soles. In the end, we analyzed the samples and chose the one that produced the best results.
During our sampling, we observed that smoother rubber surface produced a weaker grip on the leather sole. So to make the grip stronger we first decided to roughen the rubber surface with a sandpaper. Glue was then applied on both surfaces and left to dry for some time. Once the glue dried, the surfaces were heated up a bit to help the glue bond better. Both surfaces were then pasted and hammered together to ensure a strong bond. As a last step, the final sole was cleaned up in order to give it a neat and finished look.
Another option, we considered initially, was to stitch the rubber sole to leather, but we eventually decided against it. The hand stitch would very likely tear the soft rubber surface, and if we used hard rubber instead, then the stitches would result in cracks on the rubber. Below videos show how we applied rubber sole during our sampling. The method is very raw and manual, but for our production purposes, we plan to automate some of these steps. This will help artisans save their time and will also make the process less error prone.