Plywood Face Check

Read lots of builds and never have heard of this being a problem. I have seen tons say marine ply is not needed. I chose birch for my big sump because it is relatively smooth compared to oak plywood, and it is great for painting. Besides at only 72 by 36 I'm not needing tons of structural support like many of the monsters on here. Mine has only been epoxied for a year, and since I poured a quarter inch on all faces in 3 coats I'm never going to know if the faceply delaminates, but I dought in my case it will matter. I could see it being a problem in the builds that only have a super thin layer of epoxy, if there is something that can flex, I could see brittle epoxy not reacting well to that.

I just don't see it happening unless you REALLY screw up your build i.e bad angles, bad joints, no bracing etc...etc...

Never heard of face checking being a problem for plywood aquariums.

I believe West Systems was referring to boat building techniques, when you bend the plywood to fit the contour of the framing, where the face of the outside radius will check.

In that 10+ year old thread at the reef forum, I think the checking was based on some anecdotal evidence, where some plywood was fully exposed to the outdoor elements. It never actually happened to anyone's aquarium.

There was also a misconception of epoxy coatings not being waterproof. Epoxy has many of the same characteristics as acrylic. Neither epoxy or acrylic is considered waterproof, because when the surface layer of either material is exposed to water or moisture, they will absorb trace amounts of water. That water isn't permeable because the moisture content is too low before it reaches supersaturation. Acrylic or epoxy resin are perfectly suitable to build aquariums with, especially those epoxies which are solvent free and 100% solids.

I think one problem when building plywood aquariums is that the safety factor often gets ignored when it comes to waterproofing. If the glass viewing panel has safety factor of 3 or 4, then the waterproofing should be to. Meaning that you'd use 3 to 4x times the bare minimum. So if 20 mils thick is considered the minimum to waterproof a tank, then you should go with 3 or 4x times that, or 60 to 80 mils thick. That kind of common sense often gets trumped by ambition. I'm guilty of that for sure.

I have a test tank that I built in a thread on here years ago that is still going. I did not use fiberglass for any part of it. Best advice is to choose your waterproofing technique and research similar builds. There is plenty of info on here for most anything you could ever want to know about waterproofing.