# What to coat concrete with...



## adkaqua (Apr 27, 2018)

I made a foam 3d background, covered with hydraulic cement. Its cured about 2, maybe 3 weeks. It's going to be sponge painted to make it look less like concrete, more like stone. I don't want a) my paint to wear off, or b) many months of pH through the roof from leeching.

I've heard epoxy. I've heard fiberglass. Has anyone worked with either doing a similar project and had good luck with one or the other? (Pic is early on. There's another section to get it all the way down length of tank, hiding internal sump. I'll also need a way to seal the concrete/foam I use to fill the gap between front panel and rear, from side wall of sump. So fast curing is ideal)









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## Michael (Jul 20, 2010)

Instead of normal paint, you might use an acid-based concrete stain. This will penetrate the surface and should not wear off. It will also help neutralize the pH of the concrete. A further acid treatment (vinegar) should help with pH.

Whatever method you choose, try it on a test piece first.


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## adkaqua (Apr 27, 2018)

Yea I learned that lesson the hard way (testing). 

I never etched concrete before this. annnnnd just used full strength muriatic acid. Which rapidly took awake more than expected haha. I had to basically redo the entire piece for the front of my sump

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## adkaqua (Apr 27, 2018)

I debated on stain but I don't get the detail with that. I might stain it all a solid color, but I really want to make it look like granite. I have an assortment of acrylic paints. Stain would certainly be easier to make it all a solid color and then go from there. I just don't want to stick a chunk of concrete in there and call it good. I've put a lot of time into this rebuild. I want it to be on point. 

3d background with sandfall. Internal sump with fludized bed. Dennerle soil. Redoing all the silicone. Switching it to rimless. It's gonna be awesome. . if I do it right

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## mistergreen (Mar 3, 2007)

You can stain with multiple colors to make to look realistic. Stains can be expensive but you can buy a small multi-pack online.

https://www.concretecamouflage.com/cat-sample-kits.cfm

The stains go a long way. A 12 oz bottle is more than enough. The colors are intense so I mix 1:3 stain:water to it.

You can also add silica fume to the cement mix to neutralize the pH also. I think 20% of the cement. It turns the calcium hydroxide to calcium silicate.


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## adkaqua (Apr 27, 2018)

Oh cool. Never heard of that silica stuff. I'll have to look into that

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## mistergreen (Mar 3, 2007)

Silica fume is used to strengthen concrete because it's smaller than sand so it makes a tight matrix. It also has a side effect creating calcium silicate. People also use Kaolin clay which has the same effect.

I just noticed you're using hydraulic cement. Work fast! That cures fast. Also, it tends to be brittle.


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## adkaqua (Apr 27, 2018)

Oh yes. Haha very brittle. Another reason I was debating on clear coating it with the bar top epoxy

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## mistergreen (Mar 3, 2007)

If you don't mind a rougher texture, you can add sand to regular portland cement to make mortar. It'll be more durable than plain cement. Also use the liquid concrete acrylic additive to your mixture instead of plain water.


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## adkaqua (Apr 27, 2018)

mistergreen said:


> If you don't mind a rougher texture, you can add sand to regular portland cement to make mortar. It'll be more durable than plain cement. Also use the liquid concrete acrylic additive to your mixture instead of plain water.


Rough texture is perfect actually.... Will really be able to make it look more like granite. How long do I have to let that cure if I add the extra sand and stuff? Same time as if I mixed it normally. I like that....

And hadn't seen or heard of acrylic additives either. Hah. I'll have to check that out, thanks!

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## mistergreen (Mar 3, 2007)

The acrylic additive is this 
https://www.homedepot.com/p/Sika-1-...hesive-and-Acrylic-Fortifier-471643/205116870

And mortar is 1:3 cement:sand

You can buy a bag of premixed mortar actually, in the tiling section. They come in several color and some have acrylic fortifier mixed in.


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## adkaqua (Apr 27, 2018)

I like the simplicity in that way hah. I'll have to swing by Lowe's and see what they have. Or make USPS hate me even more (sooooooooooo many boxes in the last month, setting up a home business growing aquarium plants in addition to my personal tanks) and get on Amazon with prime haha

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## mistergreen (Mar 3, 2007)

As for the pH, once the mortar cures (2-3 days to a week), you can put it in a weak acid bath for a few days to remove the calcium hydroxide. Don't use straight mutric acid lol.... mix water into it, maybe 10:1.


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## adkaqua (Apr 27, 2018)

Yea straight muriatic did quite a number to it.... Which is actually why it's not finished already. I had to redo whole sections. Lesson learned. 

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