Designing with mortar - The Planted Tank Forum
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post #1 of 6 (permalink) Old 08-15-2006, 07:50 PM Thread Starter
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Designing with mortar

I'm interested in creating a vivarium using mortar for the background to create a nice stone look. I've found a lot of pictures but I'm having trouble finding instructions on the whole process. Could somebody please point me in the right direction?

Thanks :-)
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post #2 of 6 (permalink) Old 08-18-2006, 05:28 AM
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lucky for you i happen to know quite a bit about concrete.

mix mortar with some sand or fine gravel. make sure its a uniform mix. dig down into the corners of whatever you're mixing it in (i would suggest a wheelbarrow it makes it easy to transport the mix, which is very heavy) and make sure there arent any pockets of sand in the corners. use some type of tool to mix it, you dont really want it on your hands too much. it dries in the cracks of your skin and irritates the hell out of it. a few spots wont do anything you're ging to get it on your hands there no escaping that but you dont want to shove your hands in it.

after you have a uniform 'dry mix' add a little water and mix it in until the mix appears dry. add a little more and mix it again until its dry. keep doing that add water stir until dry (or damp) until you have a uniformly moist but not 'wet' mix. there is a very fine line between good workable concrete mix and runny slop. you'll see, one too many little squirts with the hose and you'll have concrete soup. this characteristic of mortar makes it more difficult to make a good mix with a small amount of it, but since concrete is heavy and hard to work with, a smaller amout is less physically demanding to mix. go for the biggest mix you can manage in the wheelbarrow. putsome of the bags in there and think about how much it'll weigh when its wet.

keep it moist while you work, too. once it dries its no good. a small spritz and a few turns every so often is fine because it dries on the surface first.

you're gonna need a really tight, sticky, almost dry mix for sculpting rockiness on a vertical wall. you wont get that if you've never worked with concrete before. you're going to make soup of it, everyone does. i did. after a few tries though, you'll get it, it jsut takes a few tries to get used to it. you'll see, you'll need less water than you think. remember: the more uniformly mixed the better i cant stress that enough.

even if its not 'soup' but just wet enough that your hand will get wet if you touch the mix it wont work for a vertical wall. it wont stay up. probably the easiest way for a beginner to do what you want to do is to construct the wall on he ground flat and wait for it to hardnen then stand it up.

as far as what to mix and how much, i have no idea. i know all this stuff because i used to work for a mason and they had me mixing it up in wheelbarrows with a shovel. they'd say like, 8 shovels of sand 4 shovels of mortar and 2 shovels of portland or some crap like that, and i'd have to mix that suff that way all day. man i dont miss THAT job. anyways, i have no idea what type of mix you should be using. you're gonna have to do some research to find that out. or if you know a mason ask them. i dont really remember any specific mixes we did but they were different for different applications. some are stickier than others but what you should be researching is how it will effect the water conditions (i suppose to get around this you could seal it with something non-toxic) and how it will react to being underwater all the time. you dont want it to crumble or crack.

how big is this going to be?

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post #3 of 6 (permalink) Old 08-18-2006, 05:37 AM
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post #4 of 6 (permalink) Old 08-20-2006, 06:27 AM
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I made a fake rock wall for my bearded dragon enclosure. I am sure the process would be the same for the fish tank only with some sort of safe sealant over the "rocks". I know on Chuck's site he has some instructions on how to do this. Also on a reptile site I will look for they show it as well. I used silicon sealant and styrofoam for the "rocks". The instructions said to use paint thinner (!) to make the rocks look real but I just scored them and gouged them with a utility knife so they looked like pieces of rock. I then used the sealant to attach them to the wall. Let it dry for a day, it will take that long to pick up the pieces of styrofoam everywhere! Then I took spray foam insulation and filled in the gaps. It looks more natural but it will expand so keep it in mind when it's drying. You can also use the spray foam insulation to attach ledges etc. Then comes the mortar. Sammy P is right, it is hard to get the consistency right. I used a large plastic tub to mix it in. I then applied it with paintbrushes and foam brushes to get in the cracks. The correct consistency was acheived eventually but it dried really quickly to almost being unusable in the bin so I had to work fast. Even then it was really thick. I only mixed a little at a time as it took a day to dry all the way. Sammy P is right that it only takes a little water. I found that if it got too thick and dry that I started the mix over, adding water just didn't make it right. The final coat was paint and that's where I mixed the sand in. I did 5 coats of the mortar then I painted it. I mixed the sand in with the paint because the mortar was tough enough already. I did this after the enclosure was built and the walls were vertical. It was a mess, so if you can, I would take the advice Sammy P gave and do it flat. I will post pictures in another post of the stages of this thing. It was a mess but well worth it. I know people who have done this in their aquatic tanks have used epoxy or some kind of safe clear sealant, but I don't know what that exactly was used. I would def use styrofoam to make the rocks though, or fiberglass as others have used because shaping them with mortar would take a long time but it's up to you! The styrofoam gives a flatter rock look but you can remedy this with adding more chunks on top of existing chunks. I cut the styro up in jagged pieces and siliconed them up in a puzzle-like manner. I added more pieces on top of them in no type of pattern and used the spray insulation to add more texture and bumps to the rocks. Pics are uploading, I will post them next.

Best advice...use a dropcloth and be patient! Let the mortar dry a full day in between coats even if it says "quick dry". Set a fan up on it to help it out if you do this inside because you'll wake up ready to go and realize there are still wet patches, and have fun!
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post #5 of 6 (permalink) Old 08-20-2006, 06:51 AM
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Here are the pics but I have none of the first parts of the process.

1.) cut styrofoam in pieces and gouge out holes and chunks to make them look rock-like. Secure them to wall with silicon sealant. Hot glue is faster but melts through the the styrofoam and that's never good. Allow a full day for them to dry.

2.) buy spray foam insulation in the can. Use it to fill in gaps and add texture to rocks. You can also use it to secure ledges etc. A little goes a long way and it is STICKY. It hardly comes off once it starts to dry tacky. Be careful it sucks when it gets on your hands.

3.) After that dries I used a large plastic tub and divided the mortar mixture on the bag to the amount I wanted for one coat. Mixed that and applied to wall. I just slopped it on. It looks more realistic that way. You can't really mess the application up. Use paint brushes and foam pad brushes to get in cracks. Let dry for a day with fans. Repeat this 5 or 6 times. You will lose some detail in this so make sure you overdo the detail in the earlier processes because the coats get thicker and fill in your gaps if they are not deep enough. Here are pics of what this looked like for me:

full view of wet mortar:

Full view of semi dry mortar:

Some pics of the details and ledges:

dry mortar:

4.) mix paint and sand together and paint the wall. I also added sand to the tacky paint because I wanted it to look sandy on the surface.

(I added detail to mine because this was my final step)

5.) After paint dries, find out what kind of sealant will be safe and apply as many coats as needed. I hope this helps! Let us know and show us some pics! Any other q's you can pm me.

Shopping list:

Home Depot:
-1 small bag of mortar. Some use tile grout but it was too expensive. I used a small bag of mortar and still have some left over. I considered this a large project.

-1 or 2 cans of spray foam insulation in a can

-1 or 2 tubes of silicon sealant

-lots of brushes you can throw away after use also a few foam brushes. You can get packs of these at wal mart too.

- 1 bag of play sand

-Paint from anywhere if you desire. The mortar will dry gray.


-The only place I could find big slabs of white styrofoam. The thicker the better. You can also use foam of different shapes you have lying around. I used 4 or 5 slabs.
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post #6 of 6 (permalink) Old 08-20-2006, 06:56 AM
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The issue with concrete/mortar/cement works is the pH. When cement is mixed with water, the pH will go instantly to 13. As it cools down and hardens, the pH will gradually go down to 10 and eventually 8. Then it needs some time to completely cure and gains strength, which process of lowering the pH to less than 8 might take weeks to months. Keep this in mind if you are going to plant the concrete with epifits. The water collumn might get affected as well for some time, but it doesnt matter if you seal it with epoxy and paint. A great alternative to making works above and inside water is using what they say as "Great stuff" which is basically a urethane foam from a can which hardens upon sprayed out and ready to colour after a short while. Check out for vivarium works. You are not alone as I'm in about to start creating a 500 gallon paludarium pond and will be doing lots of mortar works.

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