Filter and Mesh Types
If you are going to be grading and sorting very small partiles, you need appropriate filters sizes and materials. Both are important to a degree.
Filter materials
You got two basic types of material - organic and inorganic. An example of an inorganic filter is a metal mesh. You can get coarse meshes from building suppliers, if you want finer, try ebay. The USA protects it's steel industry by banning import of these, but I daresay the USA makes lots of its own in stainless steel, as do many developed countries. "Grading mesh" is what you are looking for.
Inorganic meshes are great for sorting out material, but I wouldn't use them on a breathing system. Stainless steel contains Chromium, and while it isn;'t going to contaminate a particular concrete very much, it could theoretically contaminate an individual using the same filter for years on end. The risk is very low (Chromium isn't a problem on it's one, it becomes a carcinogen, Covalent Chromium 6, when it bonds to other compounds). But why take any risk at all?
Examples of organic filters are cotton fabric (available practically everywhere), raw silk (finest but most expensive natural product), carbon fiber mesh (expensive but very hardwearing), and synthetic foam made from organic chemicals. Foam is the cheapest, and is widely used in HEPA filters. There are plenty of other fabrics you can use too, but they all contain dyes, bleaches, and fixing agents. They can be used, but they will add a little contamination to your mixes, in terms of a trace element of the dyes, bleaches etc..
Filter Types
There are different ways to rank a mesh, the most important is, what's the largest grain size that it will pass?
A superfine "silk steel" AWG49 is rated at a particle size of 3.3 microns or so. That's about the smallest I can find easily on eBay.
One other point - a filter can be damaged by material that is harder than the filter. If the material being sifted is harder than the filter material, it can damage the filter, breaking a strand, and leaving a gap for other big particles to pass through.
So treat your filters gently, and they will last.
Foam is usually rated at a particulate size too, for dust. Foam''s big advantage on wet material is that it will quickly soak up the smaller particles and the liquid, leaving the big particles on the outside. A quick squeeze to remove the liquid and smaller particles, a brush off to get the big particles off, and it's job finished. Likewise, cleaning an air filter - very quick with foam.
Do check the foam material, to make sure it isn't itself a health hazard. Talk to the supplier about who made it, in order to get the google the right data sheet for it and check.
Foam has one big advantage, it is very easy to use on damp materils to quickly seperate the wet and non-porous components of a material.
Edited 2 time(s). Last edit at 10/28/2016 07:59AM by DragonFire.