Origin
I built a box out of 0.3" (8mm) plywood sheets framed by 3" (75mm) by 2"(50mm) staffs. The box is about 3' (1000mm) each side and 2' (600mm) deep, has a floor but is open at the top. The box should act as a water reservoir, therefore needs to be waterproof (at least on the inside).
Additional materials
In order to waterproof the box I bought sheets of HDPE of 0.04" (1mm) thickness. The sheets are somewhat "semi-rigid", not as flabby as foil, but also not rigid enough to support itself, hence the plywood structure.
My Ideas
I planned to nail the HDPE sheets to the plywood sheets and weld the adjoining edges together. Additionally I wanted to seal the nails in a similar way.
Problems
Today I did a few test weldings (I could only get my hands on 0.15" (4mm) welding cord) and was less than satisfied. Probably because of the thickness ratio of cord and sheets the heat distribution was off, the sheets getting too much heat while the cord barely melt.
Question
What other ways are there to waterproof my box (preferably using most of my setup)?
Disclaimer
- I know there are easier ways to gather water, I deliberately want to
do it this way. - I welded HDPE sheets before, but always with a
thickness of more than 0.3" (8mm).
Best Answer
When dealing with water, look at marine
People make boats out of plywood, just make one inside out. They have several techniques, including involving fiberglass, but one of the most prominent is epoxy systems that give you a lot of options. One such is West System epoxy.
Keep in mind water is heavy (1 tonne per cubic meter, in fact) so your cross bracing needs to be tip top.