Most people who have used a false bottom in their mash tun will experience a certain number of grain material that finds its way under the false bottom. It can reduce the flow of wort to almost a trickle. A very frustrating experience that can turn a brew day into a most unpleasant experience.
I had this problem myself, and I solved it by creating a false bottom gasket using a vinyl tube that I cut lengthwise to fit around the rim of the false bottom. The gasket ensures that the edges of the false bottom are compressed against the sides of the mash tun. It should fit snugly to keep the grain from getting around the false bottom.
Depending on how much room you have at the bottom of your mash tun, you’ll need to choose a hose with the right thickness. For my purposes, I chose a vinyl hose that has an inside diameter of 13 mm (1/2 inch) and an outside diameter of 19 mm (3/4 inch). This provides a sturdy hose to use for a gasket.
I cut a length of hose about 3 cm longer than the diameter of the false bottom (just to be safe) and cut a slit at one side of the hose. Then I applied the hose along the edge of the false bottom and I cut the hose just a tiny bit bigger than the circumference of the false bottom. I did this so that the hose would push out a little further than the diameter of the false bottom, creating an air cushion between the edge of the false bottom and the sides of the mash tun.
When inserting the false bottom, the new vinyl gasket gets compressed into place at the bottom of the mash tun, creating a seal that keeps grain from getting under the mesh barrier. It’s a simple, but effective solution to a very annoying problem. No more clogged mashes.