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Everyone I talk to tells me that there is no product on the market that can be applied to concrete as a non-toxic waterproofing agent.

Can anyone shed some light on this? 

How do these folks like "Morningstar" who build concrete tanks in 3rd. world countries solve this problem? 

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Let alone concrete swimming pools and water slides here in the USA, though they're less common now than they were when I was a kid... I guess I just assumed the coating was non-toxic!

Someone mentioned "Thoroseal". It claims to be ok for potable water.   

Umm...wax is pretty non-toxic waterproofing agent...

According to the maker of Thoroseal, it is not suitable for use in water that has a pH of less than 7.2...which may put a crimp in your AP plans...

Thanks Vlad..... Point taken on the Thoroseal. Are you serious about wax? Any specific kind?

Absolutely Paraffin wax is a very safe bet (pretty high melting point). Carnuba wax (a vegetable based wax) has an even higher melting point in case you live in Hades. Even regular old bees wax might work if your concrete tank is relatively shaded and if it doesn't get too scorching hot where you live (it has a much lower melting point [about 46 Celcius] than either paraffin(50-70C) or carnuba (70-80C).

...but paraffin wax is probably your best bet, both economically and because of some of it's mechanical properties...Many folks the world over have used it to seal their concrete tanks.

Here is one (of a number of threads here on the forum) on the topic. Chris Smith nicely describes the 'two pronged' method he uses to seal his tanks...

There's at least one 'how to' with pics and all that I remember seeing on the BYAP (I think) forum a long time ago as well...but basically it's pretty much what Chris S describes. (i.e Melt the wax in a pail/bucket/drum then paint it on the concrete...then use a torch to melt it into the concrete. This will get the wax into all the tiny little pores and cracks. The brush on a second layer over top of the first one. That seems to pretty much be it...

Just did a search for low pH Looks like Thoroseal FX100 is formulated for "soft water situations"  Since we do live in Hades (South Texas) the wax might be an issue. Guess I'll look at the $$$ to make a decision since both Thoroseal  FX100 and Wax would be suitable for Potable Water.

Only beeswax with it's lower melting point (45C) would be an issue.

70C is about 160 degrees Fahrenheit...if your tank water is getting that hot, you've got bigger problems...

Actually, if your fish tank is getting that hot...salt the tank to 8ppt and throw in some onions, carrots and paprika and call the neighbor over for some fish stew 

Yup, looks like the FX100 might be work. Just be aware that the term "acrylic polymer" and/or "acrylic co-polymer" are industry code words for "vinyl". So look into that by contacting BASF. You may (or may not) care about the phthalate content of vinyl (still legal in the United States, but banned most elsewhere in the first world in potable water, food containers, children's toys, hospital products and other stuff).

The reason the paint industry (and other industries) have taken to calling vinyl an acrylic co-polymer is that most clients know that vinyl is a cheap ass-chinsy replacement for real acrylic. It has vastly inferior mechanical properties and is prone to leaching since (chemically speaking) no covalent bond can exist between the vinyl and the phthalates that make the vinyl pliable and elastic.

So check that out with the manufacturer (BASF) if you care. See whether it is real acrylic that they are using, or a vinyl polymer. (Oh yeah, the reason you might care is... vinyl phthalates commonly used by US industry, or by foreign industry for the US market, are a particularly nasty type of hormone disrupting carcinogen, but are part of what makes vinyl much more economically attractive than say acrylic or 'real' plastic like HDPE, LDPE, etc)...Given the price, they may actually use real acrylic.


you might consider a sealer like the concrete its self! a friend used a mason sand mix with Fiberglas which he mixed and troweled on. or if you cant do that I made a couple tanks using pond liners. several different thicknesses and they are food safe. check with local garden  shops!

A member of the community (a spanish aquaponics network) is using "Rubberizeit" to seal both on concrete and wooden aquaponics sistems that he builds. I did a little investigating on the product and they have a fantastic claim so I will quote them:  

"RubberizeIt!™ is the only VOC free non-toxic paint-able liquid rubber on the market.  Be sure that all of the materials chosen for an aquaponics system are non toxic or that the portion of the material, which comes in contact with the water in the system, is coated with RubberizeIt!™" Source:

End quote; Their product label says that RubberizeIt can be used for aquaponics sistems as you can see in this photo:

On their website they have page dedicated to aquaponics

My friend Alex Cruz is the one using it and he says its suitable for aquaponics. I have no experience at all with the product so I cannot confirm this myself but I do trust Alex Cruz.

The product seems tuff as per following video. 

Hope this information helps you.


I bought some of this for a different application, but it's supposed to work as a pond liner too:

I have tried both wax and rubberizeit. Wax??? Rubberizeit great stuff....

We are in the planning stage of doing large cement tanks and grow beds.  We have one 900gal cement tank and a just finished 2000gal (still drying) Having a good smooth finish with rounded corners is the way we like it for ours.

There are some marine epoxies used to seal ship water tank that also looked good but we choose LR.

I am a contractor that specializes in high end koi ponds. I have used "Ruberize It" to seal concrete pond . It works! No voc. I have had good luck with a brush, and with a sprayer.

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