Concrete catchment crack

[eigoya]

?We’ve had a hairline crack on our catchment tank for years ( since earthquakes in ‘18?). We were always going to patch it from inside (someday), but now I wonder: can I patch it from outside (with Flexseal or similar.)? It isn’t leaking much but moss is now growing so I’d like to clean it up without diving in. Has anyone done this? How effective might it be? Any and all speculation welcome…

[terracore]

A friend of mine had a concrete catchment tank under his house that was leaking through a crack. He patched it from inside with a concrete patch product, largely going by feel since it was dark and much of it was under the water line. He wasn't optimistic but it sealed the leak.

I would think in your scenario you would want to seal both sides of the crack, one to keep the water in and the other to keep the moss out.

[Durian Fiend]

I don't think patching it from the outside would last for long. Water will still be seeping under light pressure through the crack from inside.
If the moss on exterior of tank is the most troublesome aspect, scraping that off would be an easy job.

[eigoya]

The moss is not the most important, but it is the only reminder. I imagine sealing from outside won’t be as long lasting, but compared to what was explained by TC, it seems easy. I may try just because I don’t see us getting in there anytime soon….

[AaronM]

Any update on the Great Crack of 2018? I am interested to know what you used and how it went.

[eigoya]

Well flexseal goes on in layers; each layer takes “24-48 hours” to dry, according to directions. I will add another coat on cracks today. Moisture existed yesterday, so I’m not optimistic but hope for harm reduction rather than cure.

[terracore]

I'm curious, what does your concrete tank look like? Is it open at the top? I'm wondering if it's possible to put a liner in like with a metal tank. My friend's tank in Alaska under his house had a concrete top and only a small service hatch. I've only seen one concrete catchment tank in Hawaii and it was being used as a swimming pool. I think the "catchment tank" moniker was for permitting or insurance reasons, because the house water came from a separate metal tank.

[eigoya]

So I applied a third layer this morning (not sure that was legal, but….) and there was no moisture. I am optimistic that I will not have to think about it again for a while (which is all I want). My catchment serves as one “wall” of my carport and is actually two 4000+ tanks. That was news: I didn’t realize for years until we got water delivered and it spilled over everything. There is a small hatch on either end.

[AaronM]

There is/was a 2 story house in Leilani on Malama that has/had a huge catchment tank that essentially encompassed an entire ground floor bedroom. Not sure of capacity but it is/was huge.