Building a Still Air Box & Monotub

Part 1 : Unit 4 : Building a Still Air Box & Monotub

These two steps are bunched together as they require similar tools and settings. In both cases, you will be using a heated can to cut out holes in plastic boxes. Let’s begin with the Still Air Box. 

Still Air Box

A Still Air Box (SAB) enables you to work in a clean environment with minimal contaminants, which is vital during the first few cultivation steps, from spore germination to inoculating grain spawn.  You want to prevent bacteria, molds and competing fungi spores from contaminating your growing environment and destroying your grow. To build a SAB, you will make two 4-6″ inch holes in a 60-100 quart clear plastic box using a large heated can.  Yes, you got that right. It’s just a big, clear, plastic tub, turned up-side-down, with two holes in it.


Once you’ve mixed your bulk substrate with grain spawn, you will place the mixture in a Monotub and allow it to incubate for ten days. In order to initiate the fruiting stage, you will need to introduce Fresh Air Exchange (FAE) through the 8 holes around the tub.

You will cut out 8 holes in your 40 quart tub and cover them with heavy duct tape. When the time comes for FAE, you will cut open the holes with a scalpel and cover them again with porous micropore tape. This will allow a bit of air flow into the tub while keep contaminants out. Cutting these holes requires patience and attention. And lots of fire 🔥. 

Let’s get to it!

Still air box for mushroom cultivation
Still Air Box For Mushroom Cultivation
Making a monotub
Making A Monotub

Building a DIY Still Air Box (SAB) for Clean Work

Items needed
Notes & Tips
How to build a still air box
Items Needed To Make A Sab

Video Tutorial : Building a Still Air Box for Clean and Sterile Work

The video markers above 👆🏼correspond to the the various Steps in this Unit. Click on them to skip to a Step.

Step 1 : Mark the Height and Spacing for the Arm Holes on the Box

Remove the SAB lid and place the SAB upside down on your table or work surface. 

On the broad side of the SAB, take two measurements and mark them with a sharpie: The height for your holes (4-6 inches up) and the distance between the holes (10-12 inches apart), as shown in the diagram on the right. 

Positioning the holes correctly will give you comfortable access to work inside the SAB. 

Still air box hole spacing

Step 2 : Cut out the Two Holes on the Broad Side of the Box

Place an empty, dry metal can on the gas stove and turn on the heat. Allow the metal can to heat for a few minutes and then carefully secure the hot can by clamping on to the top of the can with the vice grip or pliers. Apply the hot part of the can to one of the hole markings you made earlier, and gently push it through. If the metal is hot enough, it should make a clean hole through the plastic. If the hole is not large enough for your forearm to go through it, you can repeat the process above and simply expand parts of each hole by cutting out little crescents around it with the hot can. The arm holes do not have to be perfectly circular.

Building a DIY Monotub for Growing Mushrooms

Items needed
Notes & Tips
Making a monotub
Items Needed To Make A Monotub

Video Tutorial : Building a Monotub for Growing Mushrooms

Step 1 : Mark Air Vent Hole Positions on the Tub

Rinse and clean the monotub if needed, and place it right side up on your work surface or table. Draw a line about 3 inches high from the bottom of the tub. (Later, when you put your bulk substrate and grain spawn into the monotub, this line will help you level out the mixture so that you get an even thickness throughout your mycelium cake.) Next, mark 3 holes on the each of the broad sides of the plastic tub, where the middle hole is lower, as shown on the right.  

Monotub fae hole positions

Step 2 : Heat Aluminium Can and Punch out Holes on sides of Tub

Grab an empty coke can and optionally, remove its top with a can opener. Get a good grip of the can from its bottom side using pliers, and heat up the top of the can for a minute or two on a gas burner with high heat.  Gently push the can top against one of the hole marks on the tub, and then lightly twist the can. The can doesn’t need to go through the plastic entirely, but just enough for you to be able to push or cut the remaining plastic around the hole later on, without too much effort. Re-heat the top of the can and proceed to cut through the rest of the holes around the tub. Plastic residues on the can may go up in flames when heated, so be careful of the fire, and of molten plastic dripping off the can. Once all the holes are completed, use a knife to carefully smoothe the edges of the holes from and remove any protruding plastic bits. This will provide a smooth surface for the gorilla or duct tape you are about to apply on the holes.

Step 3 : Cover Holes with Gorilla or Duct Tape on both sides.

Proceed to cover up the holes with wide gorilla tape or duct tape, on both the outside and the inside of the monotub. Make sure the holes are covered well, with an overlap,  so there are no air gaps between the tub and the tape.

Next Unit: Using a pressure cooker. The core tool of your mushroom cultivation journey, a pressure cooker. Dangerous if not used correctly or mishandled. Make sure you totally understand the next module.

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