Very difficult to seal the acrylic against the EPDM liner. Problem is getting the EPDM to smooth out like a gasket, allowing for compression and a good seal. Secondly, the thickness of the EPDM may not be sufficient to fill the rough surface of the plywood. Plus, you hve cosmetic issues with the pass-through bolts. However, we have done tanks where the bolts have been used for a "porthole" look.
You might consider building the lower tank as a wet plywood box. On the front side, cut a viewing window, leaving a "window frame" of approximately 2". Seal the inside of the plywood box with epoxy and sand the back side of the windowed front smooth. You can silicone the acrylic to the inside of the window frame. 3/4" acrylic can span the 4' or so without bowing, given the short height. However, at 4' wide, you might want to leave a center member by cutting two windows. This also allows you to add a bulkhead rib inside of the tank to prevent bow along the long side.
Our product of choice is WestSystems epoxy. A gallon of resin should do the job. We also suggest a fillet in each seam, and then reinforcing the inner seams with tape. With a bit of sanding, the tape can disappear. This product leaves the inside of the tank somewhere near a golden color, depending on the plywood. If you would like to darken the interior, use a WATER-BASED dye prior to application of the epoxy. Aniline dyes are a good choice, over a good quality plywood, a nice uniform color can be achieved.
I've got about half of a plywood tank DIY article finished. Any interest? I could tune it up and get it posted in a week or so.
You might consider building the lower tank as a wet plywood box. On the front side, cut a viewing window, leaving a "window frame" of approximately 2". Seal the inside of the plywood box with epoxy and sand the back side of the windowed front smooth. You can silicone the acrylic to the inside of the window frame. 3/4" acrylic can span the 4' or so without bowing, given the short height. However, at 4' wide, you might want to leave a center member by cutting two windows. This also allows you to add a bulkhead rib inside of the tank to prevent bow along the long side.
Our product of choice is WestSystems epoxy. A gallon of resin should do the job. We also suggest a fillet in each seam, and then reinforcing the inner seams with tape. With a bit of sanding, the tape can disappear. This product leaves the inside of the tank somewhere near a golden color, depending on the plywood. If you would like to darken the interior, use a WATER-BASED dye prior to application of the epoxy. Aniline dyes are a good choice, over a good quality plywood, a nice uniform color can be achieved.
I've got about half of a plywood tank DIY article finished. Any interest? I could tune it up and get it posted in a week or so.
