How to waterproof a pallet planter box

Does anyone have an recommendations on how to waterproof the bases in a planter box made from pallets?

Picture a pallet standing up. The bases on each runner/rail have been filled with a piece of wood. I tried this once before and just used silicone around the join but it was no use, water still came through when I watered the plants.

What would be a clean, simple way to water tight the edges of the bases? I've attached an image of what we are trying to create. A friend suggested just adding rubber to each planter compartment.

blkhawk4 years ago
Some line the inside of the planter with a plastic film.
dougfirr (author)  blkhawk4 years ago
@blkhawk - what "kind" of plastic? Surely not cling film (ceran wrap)?
I should have said plastic sheet. Many how-to planters suggest lining the inside of the planter with plastic sheet.

plastic sheet
dougfirr (author)  blkhawk4 years ago
Ah I see thanks for the info. I'm thinking just using silicone to make it stick?