How to finish plastic
The first thing to remember
We’re going to drive this home again: the more accurate your mould, the less work you’ll have to do in post-processing. If you’re going to make 100 bowls, making sure your mould is super polished might save you a few minutes of sanding. Times that by 100 bowls, it definitely adds up! So take it from us: spend time on your mould. And if plastic does stick, head to your local hardware store and pick up some mould release, this should help.
Soft plastics vs hard plastics
When working with soft plastic, like HDPE, PP, LDPE they will have a nice matte finish, and will never be shiny. They are more flexible and are harder to work with, and there are a few techniques you can use to finish:
- When finishing edges, use a basic knife to cut the rough parts off
- When finishing surfaces, use a blade or if you want to smooth out a surface
- If you have plastic, stringy fibres, you can use a heat gun over the surface. Be careful though - this will change the texture of your product
When working with hard plastics like PS they will come out with a smooth and shiny surface, and are much easier to polish and can be sanded very well.
- When finishing edges or surfaces, you can sand by hand or use a machine, from grain size 450 to 1500.
- When polishing, you can use toothpaste (yep!) but only on white/light surfaces. For anything dark or with a colour, we suggest using a normal polish from the hardware store (we use one from the car industry). Polishing this way is very labour intensive, but comes out with some beautiful results!
Marking your products
Right on! OK now you have a pile of your products, it’s time to mark them. It’s very important to make sure that once your product has reached the end of it’s lifespan (hopefully that’s a long time away) that you, or the next person knows which plastic type it is so they can shred it and remould it again. As well as this, working with the Precious Plastic process is labour intensive: you have to collect the plastic, separate/shred/clean it, mould it, finish it and mark it. So not only can this mark be used to show the plastic type, but also as a kind of trademark for plastic products with a higher value. You can buy them on the bazar here.