DIY Air filtering solution

I’ve been wanting do some slip casting for ceramics for a while, so I’ll have to be working with dry plaster and dry clay slip indoors.

Slip casting is a really really cool process - It involves pouring liquid clay (slip) into a plaster mold. The plaster removes water from the liquid, causing slip to solidify at the interface. After you have the thickness you need, the slip can be poured out, and the mold removed leaving a clay positive of the plaster negative. The workflow once you have liquid slip and plaster molds is quite safe, however, mixing dry slip into liquid suspension and making plaster molds from dry plaster is quite tricky.

Exposure to these dry powders can be toxic over longer periods, so I’m hoping to get some kind of air filtering for small particles going on…

The room is essentially a small office, 10ft by 10ft by 8ft ceilings (800cf).

My plan is currently three-fold

  1. Wear a p100 respirator - I have this from my glaze mixing days and works as a simple last-line-of-defense PPE tool.

  2. Install a vacuum hose near the work area (mixing containers/open buckets), opposite where I’m located to draw the material away from my eyes/nose/mouth.

  3. Have air cleaning/filtering going on in the room in general. I was looking at things like the powertec air filter that’s in the wood shop, but they only have 1um filters. The particles I’m looking to filter out are much smaller. It would be cool to have a modular setup where you replace filters and change their rating as well (type of particles extracted). I think a solution to this problem can help with other needs too (such as forest fires).

I found this mobile air cleaner kit being used by many woodworkers - Which might be a good starting point for a design Mobile Air Cleaner Cart | Jays Custom Creations. It uses a blower motor from a furnace to circulate air through a box with ~4 furnace filters.

One of the reasons I’m posting this is to seek some advice regarding this whole endeavor

I already have #1 (PPE), among #2 and #3, which one should I prioritize?

If I’m building #3, is there cheap source of blowers/motors - How would I plug that into power? I haven’t used motors like this before…

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be careful about just how much moving air you have going on in the room. You don’t want to be stirring up dust that has settled quietly onto surfaces.

Your dust mask (if properly fitted) and learning how to move the dry material from bag to mixing containers will go a long way. Don’t just dump in the dry material. Use a scoop and and let it slide off your scoop with as short a drop as possible. Storing your dry goods in bags is also a good way to fill the air with dust every time you move them. The basically behave like bellows. try and use Rubbermaid bins or plastic buckets.

Clean up everything with with water and clothe/sponge. if you vacuum it up you will just make more of it airborne.


When researching highly toxic/sensitizing wood dusts, one of the things that surprised me is how much exposure comes through your eyes/tear ducts. Unless it is a lung-specific health hazard, consider a full face mask with P100, if the health concern is lung-only, then ignore this.

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How large are the powder containers/molds that you have to handle? Would it be practical to use a small or medium sized glovebox for the mixing stage?

This sort of thing:


My first thought was that even with good air filtration, the powder is eventually going to coat everything in the room, then will become airborne all over again any time it is disturbed.

Going down the old safety hierarchy, I suppose this would be the 3rd step down, “engineering controls.” PPE is usually considered the last step, and the least effective.

Edit: You would probably still want filtration for the glovebox but you would need massively less capacity than if you were treating a whole room.


Have you considered some of the PCO/catalyzing filters as one of your stages?

Details on PCO in article below

Here’s a small scale consumer one

I know much larger scale industrial units exist.

Also what about air quality monitoring?

That makes a lot of sense, thanks jim.

I suspect that plaster mixing and slip mixing will be quite rare, with most of my time spent casting and painting the cast pieces :slight_smile:

Do you know if PCO’s are able to help in scenarios where the dust is inorganic as well?

I was talking about air filtering subject yesterday for an incoming project. It still a raw idea but I plan to hack the air inlet of a snorkeling mask to be fed with clean fresh air either from the outside conveyed in a duct or maybe from filtered compressed air as @Metal_Janet suggested during the conversation. There are commercial devices like this in the market for hazardous environments but they are really expensive, in contrast a Snorkling mask cost $35 at Amazon or $69 at Canadian Tire plus the cost of ducts and adaptation. Depend on where will operate let’s say close or far from a window it may need a centrifugal fan. I hope this idea fits into your project. Cheers. Gustavo

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