I have a pair of shoes which are very slippery on snow, ice and other smooth surfaces. I sometimes have the problem at home if the floor is wet. How can I make them less slippery or in other words - how to improve the friction of these shoes? I am interested in making them less slippery on ice and on other surfaces too.
Try mixing sugar/salt with rubber glue. Coating the bottom of the shoe should do the trick. The sugar/salt grains texture the glue like sand paper. The glue...umm...sticks the grains to the shoe...
Just make sure you don't use caster sugar, as the grain size is important.
I sometimes use hair spray which I apply on the sole several times and waiting for 1-2 minutes between each spaying to let the hairspray become dry. This improves the friction, but unfortunately has only temporary effect.
You should wear in your shoes a bit. Walking on the smooth surfaces like ice does a little bit towards making the sole of your shoes less slippery as you understand, so you should walk more on the rough surfaces, like asphalt or something stony. Also you can rub thr soles of your shoes with something abrasive, like emery paper.
Pine resin works well. A big pine near my house was cut down, and I dissolved some of the sap in a mix of acetone and alcohol (flammable!). It works well as antislip, and is clear. Of course, after your shoes pick up dus, it is less effective.
I have a pair of crocs and the rubber soles are extremely slippery on smooth surfaces, especially steel overbridges. I face even more trouble on wet tile floors.
However, one day by accident, I walked on a road (undergoing maintenance) with molten asphalt and that stuck to my soles real well. Ended up having some good traction on my shoes. Maybe if you could get your hands on some molten asphalt it could do the trick for you. Alternately, you could try some cement (Don't know about this one, just guessing)
Cut a strip of sandpaper and glue it to the sole. Try different placements for optimal result.
Try drawing lines at the bottom of your shoes using a fork. That should give you quite good grip and make it less slippery
Depending on your shoes, they can often be transformed with leather patches, or entirely new super grip soles that are designed specifically for the application you have in mind.
Your local, family-run, cleaning, key-cutting, shoe repair shop should be able to recommend something and help you with that.