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PostPosted: Mon May 19, 2008 3:53 pm
by chefkeith
iceblue wrote:By the way, hows the river tank doing?

There are just a few aesthetic glitches with it, but otherwise it's doing great. All the work put into the project was worth it. The fish love the caves in the foam/concrete island and the water flowing around it.
I look forward to building another someday since now I have a better idea of what I'm doing.

I really like some of the construction ideas you had too. This is probably the one of the most amazing projects I've seen.

PostPosted: Mon May 19, 2008 11:13 pm
by iceblue
Thank you for the compliment and I know what you mean about looking forward to doing it again.

I found very little information on the web about perlite concrete projects before I started. One of them was for building a small kiln out of a coffee can to smelt metal and others on how to make lightwieght parking structures and a kayak. It kinda felt like I was on my own with this. I know the next time I do it it will be a little different.....Just a wee bit wiser now. :lol:

PostPosted: Tue May 20, 2008 6:08 pm
by chefkeith
Not having instructions is what makes it fun. I learned more about mixing concrete from my project than I probably would of working in construction for 20 years.

I didn't see much info about making lightweight concrete either. I do remember that Perlite soaks up water like I couldn't believe. I'm glad you found a good mix for making the lightest non-bouyant concrete possible. I'm going to steal that recipe and some of the methods you used for building extra caves for my rivertank. I'll have to start up my old thread again soon.

PostPosted: Tue May 20, 2008 6:51 pm
by iceblue
When I first started experimenting with different mixtures to come up with the one I eventually used I had to choose between perlite or vermiculite. I placed a handfull of each in seperate containers of water. The vermiculite really sucked up the water and actually broke down into clay. I noticed that its expanded stucture looks stacked plates and once wet will squish without much preasure. Didn't seem like a good choice for submersion. The perlite on the other hand absorbed some but a lot of it still floated after a couple of days. Its basically expanded glass instead of mica like the vermiculite and became my aggregate of choice.

a good mix for making the lightest non-bouyant concrete possible

Actually the mix I used was real close to bouyant. The skin of mortar and sand that I put over it is what keeps it heavy enough to sink.

Are you going to make rock structures to fill in under your "roots"?

PostPosted: Wed May 21, 2008 11:00 pm
by chefkeith
I fixed that problem under the roots by adding waterfall foam around the top of the island. The center braces hold down the island.


I want to make some rounded corners/caves out of the lightweight concrete. Right now, I'm using a quartered bucket in some of the corners, but they don't stay in place too well and are ugly.


There is plenty of space in the corners to make something nice and to improve the water flow.

PostPosted: Thu May 22, 2008 2:39 pm
by iceblue
Chefkieth wrote:

I want to make some rounded corners/caves out of the lightweight concrete.

I found the corners of my tank to be the best place for making my caves. Plenty of room to design different shaped fish shelters.

Just a little tip, whether it works or not hasn't been tested yet in my tank. I gave the bottom of my caves a slight slope. A little higher in the back sloping down towards the entrance. I figured the fish swimming in and out of them would help to keep them clear of detritus.

You see it asked a lot on the Forum about the leaching of cement raising the water hardness and Ph. I'm pretty confident my long cure time and the acrylic fortifier I used to color my structures will make that nearly nill. Since as far as I've been able to tell you were the first here to try a lightweight concrete mix maybe you could give us clue if a solid lightwieght concrete structure has had any long term effects on your water quality. ... &&start=75

PostPosted: Fri May 23, 2008 12:17 am
by chefkeith
The tip does work. My main cave is on a slight incline and it has stayed absolutely clean. It's been about a year and I haven't had to clean the cave once.

There was alot of leaching at first, but once the concrete got a biological layer on it, the leaching slowed down. After a few months the leaching was minimal. It's been about a year now and there isn't any noticable leaching. I test the TDS almost daily and it don't go up by more than 2 ppm daily, but the TDS goes up mostly due to the fish waste and driftwood decaying. I have about 200# of driftwood in my system right now.

quickrete coloring

PostPosted: Fri May 23, 2008 3:29 pm
by will74
I used this coloring for my 125, which isn't done yet and was wondering if the iron oxide in the coloring leached out into the tank and caused any problems? I didn't think about it harming the fish on a long term basis, anybody know if iron oxide, which is basically rust would harm the fish on a long term basis?

Re: quickrete coloring

PostPosted: Fri May 23, 2008 6:24 pm
by iceblue
will74 wrote:wondering if the iron oxide in the coloring leached out into the tank and caused any problems?

You certainly got my attention. :o I did some searching and found that "natural" iron oxides as is found in the liquid concrete colors are non-toxic mineral salts that permently fix color to the medium you are using. There is only, if any, small trace amounts of metalic irons in it. Normal routine water changes should be more then enough to take care of anything that might leach into the water.

Thanks for freaking me out. :lol: The search I did makes me feel better about the whole thing. :thumb:

PostPosted: Tue Nov 11, 2008 7:45 pm
by RiftCichlids
I would like to see how your tank looks with the finished background, any chance for some photos?
I'm glad I ran across this thread and your recipe for lightweight concrete, I had something like that in mind myself. Where do you buy perlite?

Is there anything about the construction you would do different?

PostPosted: Tue Nov 11, 2008 9:14 pm
by iceblue
I bought the perlite at the Home Depot. They have very large bags of it for less then $20 in their gardening department. Usually inside.

Things I would do differently.

1. Use half the sand I recommended for the perlite mix. I like the way the added sand helped to form the structures but found it works just as well with half as much. The original formula is on page 1.

2. Spent more time sculpting the structures after I put the skin coat over it. I think it would have looked better with a harder more angular facing.

3. Not go so color crazy. :o But this I can change.

4. Make a couple of the structures in 2 pieces instead of one. Although it's a lightweight concrete mix it's still a concrete mix. It's about 40% lighter then regular concrete but 2 of my pieces still weigh close to 90 pounds.

5. Not base my overall design on how my filter system will work. This limited what I could do but. should make for an almost maintenance free tank. ( Will still do those weekly water changes)

My digital camera seems to pick up more color then what it actually looks. The structures to the furthest right of the picture is what the overall tank background looks like to the eye.


PostPosted: Tue Nov 11, 2008 9:40 pm
by RiftCichlids
Here is an interesting link that shows the construction of a huge tank along with a concrete background. Click on Mega tank and scroll down for the background. ... nglish.htm

PostPosted: Tue Nov 11, 2008 9:42 pm
by iceblue
The links not coming up for me.

Edit: Found it.

My tank's just a wimpy 350g. Would love to do something like that though.

PostPosted: Tue Nov 11, 2008 11:22 pm
by RiftCichlids
Wow, 90 lbs., those are some pretty heavy sections. I wouldn't want one to slip out of my hands putting those sections in my 240 G. tank.

When you tried it with 1/2 the sand, was the weight of the concrete about the same as water? That would be perfect, easy to keep in place without the added weight. I was thinking of making my background in layers that would interlock together as I stacked them. Maybe build it laying flat on a table inside a frame, one piece at a time, wrapping plastic wrap between sections as I build them to keep them from sticking together. Could use pieces of pvc pipe for dowels to hold the sections together.

Fairly large diameter vertical dowels would remove some of the weight of concrete, and could be used as passage ways for UGJs that could be directed out the front at the base of the background.
Would have to figure out a way to make them just loose enough to slide the sections down over them easily.

I like your idea of caves in the background. I thought I would try making wide cracks and overhangs along with the caves for the fish to hang out in.

PostPosted: Wed Nov 12, 2008 2:35 pm
by iceblue
The pieces that weigh a lot are very large. Most of the other sections weigh between 20 to 40 pounds. Taking out half the sand did lighten it a bit but the bulk of the aggregate is perlite. The perlite mix is already close to being buoyant and the 1 part Portland with 3 parts sand mix that I used to skin the structures gives it enough weight to stay sunk. Even my 90 pound pieces if held underwater would seem light.

I don't think you have to go through the histrionics of adding pipe to hold your structures in place. If you leave trenches or roughness in the pieces underneath your next section that should be fine for keeping them from slipping around. If you want to lighten them further you could use sand as a filler between your structure walls and wash it out after the structure has dried.

Below is a picture of one of my pieces removed to show part of my UGJ system. Instead of plastic to separate the structures from each other I used thin foam wrapping sheets. I found they make it easier to separate the pieces and make a nice buffer between the concrete and the walls of my aquarium. The foam is stuck on the piece to the right.


Here's another pic with a 1' ruler to give you and idea of the size. The structure it leans against weighs about 20 pounds.