Backyard Aquaponics
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This is the bottom of 1 of my 1000 gallon FT in my new RAS. Does anyone have any idea of how to seal and close off the depression in the bottom. I tried silicon and a scrap piece of poly. I didn't work. I don't have a poly welder, and kind of hated to experiment on a 1000 gallon tank, which is in place, leveled and plumbed. I thought of using the expanding foam as a filler and then fiber-glassing over it. My brother said that "glass" doesn't adhere to well to poly, and it could/would leak? I can't really leave it, as the solids would surely end up trapped in the large void. Suggestions anyone?

Hi coachchris

Let me start by saying that I have not used an IBC. To me it looks like a good place to collect solids for the SLO.

+1

It's not an IBC. It's a 7570 liter poly tank that is cut in half. The part your seeing is the former lid, screw off top in it's former life. I'm using a center drain that's visible in the left front. This area just needs to be "filled" and made waterproof.

Not sure this would work but you could use an epoxy resin to fill it in. If concerned about it adhering then you could use release wax to make sure you could get it out once dried and then silicon back in place. You could then clamp it down from outside with threaded rod. I know it's a bit of a full on way of doing it but I couldn't think of anything else that you could rely on.

Dan

Can you get Sikaflex 11FC where you are? It's a polyurethane sealant and adhesive and is really good for most things. It might work better at sticking the scrap piece over the hole than straight silicone.

Both ideas have potential. Thanks guys! Will look for the Sikaflex, and ask brother about epoxy idea.

Speak to a poly rotomoulder.. Ours always said to forget trying to stick or glue things to poly because of the oil content within the material. Perhaps a combination of sika and a few tack welds to hold it in place permanently. Do you have any scrap? Cut some very thin pieces, or use drill swarf, use a lighter, soldering iron, heat gun, see if you can't get it to work.. I was surprised at what Nat could do welding it together.

Ok then this is how I sealed the top manhole in a poly rainwater tank. I need the manhole sealed as I cut a 5,500L rain water tank horizontally in two. That way I got two tanks.

This over kill but it shows that Sikaflex 11FC works. I cut a piece of 5mm aluminum plate to fit the manhole and place a layer of EDM liner between the aluminum and poly tank. This was then bolted to the tank on the outside of the manhole with stainless steel bolts. That will hold back the pressure of the water.

The cavity inside the tank was filled with expanding contact foam. This was leveled off and covered with a layer of old conveyor belt rubber. It was sealed down with the Sikaflex 11FC. as the Sikaflex 11FC is flexible it should be ok. It has been close to a year without a leak.

The rubber was to make sure that the expanding foam did not contact the water.

Over kill as I said but it got the job done with materials at hand.

If you do use Sikaflex 11FC as a sealer make sure that your base of the tank is sitting on a firm base and cannot flex.

I would simply get your round scrap again, put a thick layer of sikaflex around the hole, screw the scrap on and down tight - making sure you screw through the sikaflex, then spread sikaflex over the screws and around the edge of the scrap to seal it all off.

Sikaflex sticks ok to poly, i have used it to seal black barrels, i would only think of it as a sealer in this case though, i wouldnt rely on its glue properties, it will stick a fair bit though.

I'm not sure if you're trying to prevent a leak or if you just want to blank off the depression to prevent solids build up.
If you are sure it isn't going to leak, you could just locate your SLO or pump in there to pick up the solids and save all the effort/expense.
Bearing in mind that I'm a little bit rough/lazy...

What about filling the depression with a plug of concrete?

I would worry about concrete leaking.

That small amount should not be an issue. I concreted the bottom of my RFF and have had no issues.

there may not be PH issues in some cases, however its well known that new concrete gives off carcinogens.