Cement 3D Background..My How To Guide..

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Original poster
Feb 17, 2007
Hull, Yorkshire, England
A guide to a Cement 3d Background

I want to be clear from the start, this isn’t definitive, this is just a guide to what I did, there are probably better ways to do things and better materials to use but I can only comment on what I did personally and any complications I found along the way.

A lot of people have asked me how i did it so i thought it best to write up a guide once rather then answer the same questions over and over again, lol i hope some of you find it useful/helpful.
This whole project was FAR easier then I originally thought it would be, and loads more fun, so if you are sat there thinking…looks too difficult you may want to reconsider, all you need is patience and some spare time.

Tools and Stuff

1 X 2.5kg cement (a waterproof cement for sealing leaks in ponds, the brand name was EVO-Cement it was quick dry stuff and I bought this from a shop called HomeBase in the UK)
1 X 700ml tube of aquarium sealant
1 X paintbrush (I used a scabby one from a pound shop)
1 X mixing bowl (again a cheap one will do, I used it for mixing the cement)
Styrofoam, I used the foam that comes in fish transport boxes, but any polystyrene type box will do
1 X small sharpe knife, I used one with a 3inch blade out of the kitchen.

Ok well I suppose the first place to start is the tank itself, personally my tank was a right mess! So it took me a while to clean and prep it first, I would recommend anyone that uses an old used tank do what I did and use a razorblade scraper along the glass and to thoroughly clean the tank so that it is in good condition, I then measured the tank and sat there and tried to visualise how I wanted the background and made a few measurements and came up with a few ideas. Of how I wanted it to look and how I would incorporate the filter and heater within the background.

I did all my cutting of the polystyrene in the garage…good idea!! Its VERY messy lol I did a layout of the tank dimensions on the garage floor using masking tape, this saved me taking the background in and out of the house constantly to size it up.

Getting started was difficult, it is hard to know what to cut first or what piece to put where, I used a marker pen on the polystyrene to draw out a few cracks and rocks which I could use as a rough guide, but I found that once I got started carving away at the polystyrene I didn’t use those guides much I just went with the flow really. When researching how to do this I read a guide on the cichlid forum and made a mental note of what someone else wrote which was to exaggerate any cracks or details in the rock to approx 3-4 times the size you want, because once the cement is applied those details will disappear unless they were deep/large enough to begin with…this turned out to be golden advice! And I would strongly advise anyone to take this onboard, even if you make the details too large you can always apply a few layers of touch up cement to them later. I created my background in 4 large pieces to make getting it in/out of the tank easier. Hopefully from the pictures no one will be able to see those joins but where the pieces join is something you can think about beforehand and try and work out how you can make them to fit and be almost hidden at the same time, the cement can help to cover any lines that still show though.

Ok so the difficult part was how to hide/incorporate the filter into the background, I probably had an easier job then most for this, I used a juwel filter box from the juwel aquarium range, so I basically had a box that I needed to cover with polystyrene and detail it to look like part of the background, always think about wires/intake tubes, airline hoses and water flow, even if you have a current setup that fits fine. What if you upgrade the filter? What if your heater breaks and you have to replace it? Can you remove your UGF once the background is in place? Etc it is so much easier to think about these problems now and work around them then realise your mistake later and have to bodge it to make it work.

this is my hidden filter

The background will be semi permanent! If you make a mistake in the layout/setup it will be a nightmare to put right! In fact the only way to remove this background would be to literally rip it off the glass which would destroy the background and then razorblade the silicon/polystyrene chunks off the tank glass…very messy indeed.

Ok so you have your carved masterpiece, time for a test fit, place it into the tank and take a really good hard look at it, I left mine in the tank for a full day and spent a good couple of hours looking at it in total just thinking about how to improve it, how to adjust rocks or cracks to give that added realism, initially I wanted some kind of overhead rock to give a shadowed effect across the tank, after about 5minutes in the tank I hated it and removed it straight away.

test fit…time to take a good look and make any changes

You can see my original idea was some kind or rock canopy type thing. it looked rubbish!

I also only originally panned to cover both corners and leave the back of the tank untouched, but after sitting there looking at it I decided that it would look better if the background covered the whole of the back of the tank but with a few cracks to give some depth and more of a 3d feel to it, if I hadn’t done a test fit and sat there and really looked at it, I know that once I cemented it and had it in the tank I would have hated it.

Ohh before I forget!! To create a more layerd/3d look I used the aquarium sealant to stick bits of polystyrene on top of each other to give a more 3D feel to it. Don’t be afraid to do this but always remember the buoyancy of the polystyrene! So sticking a huge rock to a tiny piece with a small blob of silicon is not the best of ideas and assuming that the layers of cement will hold it in place is maybe not the best idea either, just use a good amount of sealant and make sure there is enough surface area stuck down.

CEMENT TIME!!!! Once the test fit goes well and everything slots into place and you are happy with the way that the filter works and that there is enough clearance for cables and anything else you may have then remove the background from your tank and mix up some cement.. I did a really small amount first, just a golf ball sized scoop of cement with a teaspoon sized drop of water and mixed that up, I wanted to get an idea of texture and how it would cover on the background…too runny too thick etc add more cement…add more water…you get the idea.

messy…but fun J

I managed to get a consistency of a milkshake so it was still quite runny but thick enough to give a first good coat, the amount of cracks/caves I had created meant that the runny texture was essential, because I could literally just pour cement into caves and slop it about a bit with the paintbrush, no finesse needed at this point at all, it is all about coverage just slap a load on and make sure that all the forward facing parts and inside any caves/cracks are covered in cement…do not cement the BACK of the background…this will be the contact area between your background and the tank! So you want this to remain bare to give a good contact surface area!

The first layer was pretty quick to dry, only taking around 3 or 4 hours before it was touch dry, I left it a further 24hours anyway just to make sure.

The second layer was the same milkshake consistency again I just slapped it all onto the background making sure that it was all getting covered and no caves/cracks were getting missed. I waited a couple of hours and then placed it into the tank for a test fit and left it in the tank to finish off drying, the cement had made some of the very snug joins even snugger, so minor trimming was needed, thankfully I realised ad this stage and minor cement touch ups were not a problem. It took a little longer to be touch dry this time about 12hours ish I think, I actually left it a few days to dry…not for any particular reason I just didn’t have time to do anything else with the tank.

I then decided it was time to silicon the background to the tank, I can then wait for the silicon to dry while the 3rd layer was drying at the same time. I used a LARGE amount of silicon, I applied a big 1inch blob about every 5inches and pushed it up against the glass to make sure it was on secure, I used a LOT of silicon on the background, every background I have seen that went wrong was because the person was a scrooge with the silicon and underestimated the buoyancy of the background, I didn’t want to make this mistake and thankfully!! Apart from 1 rock which was slightly loose after the 3rd water change so I re stuck that down…easier when you have an empty tank!

Once the background was stuck to the back of the tank, I mixed up the 3rd layer, this time going for a thicker layer, more of a porridge/oatmeal consistency and again just brushing it onto the background making sure to cover it all, this time it was more difficult to apply, the fact it was in the tank made things easier…I was impatient and should have applied the 3rd layer OUTSIDE of the tank. but never mind, after 10minutes or so the cement started to harden slightly so It was becoming more difficult to spread without it crumbling, I just added a drop or 2 of water to the cement every few minutes which stoped it going too dry when painting onto the background.

the test fit went really well I thought and looked exactly how I wanted it to look

I think if I remember correctly the first layer was a Monday night, 2nd layer was the Wednesday night and the third layer / silicon’d to tank was on the Friday night, I then did a 20% 4th layer touch up on the Saturday morning…what I mean by this is that I mixed up some more cement and touched up any areas that I thought might need a bit more coverage…cracks/joins etc and I covered approx 20% of the background.

Saturday night the background seemed to be touch dry but still looked slightly damp and the silicon was hard.

Sunday evening the background seemed completely dry and looked sturdy! Time for the test! WATER!!!!!

I filled the tank to approx 30% using a 1ltr jug at a time, looking for any movement or lifting from the background, I stopped every 10jugs and poked/prodded the background to make sure it was still sturdy and in place ok, I left it 30minutes and then took it to the 75% mark, again filling it a jug at a time looking for any movement. I waited another 20-30minutes checked again and topped the tank up to the top.

check out the cloudy water!

I switched the power head from my filter on and just left it to churn the water up for me…there was a LOT of cement dust!! I packed the filter with filter wool to take up any dust in the water and to help clean up the tank.

After a day the dust settled down to the bottom of the tank in a layer, I used a siphon to get rid of most of it, but it stays in clumps anyway so it would be easy to remove with a jug or let your filter wool trap it.

I also added an airhose and an airbrick! Wow what a difference, the water really started to churn up and I wish I had put this in earlier!

You can see some of the cement dust that settled on the background, makes it look white almost

I left this water in the tank for 3 days, I then did a 100% water change, I left the tank for a day for the background to dry out and then I refilled the tank again with fresh water. And replaced the filter wool
The ph at this point stayed a steady 9.0

5 days later I emptied the tank again completely, and I filled it back up again with a saltwater mix, I didn’t do anything scientific I just added 2 handfuls of marine salt I got from my local LFS…you may be asking why, well I am not 100% to tell the truth but I think it is because the salt acts as a water softener and helps the background set solid and should stop any leeching into the water…anyway loads of other people who have done guides all said about using it. so who am I to argue, lol

I left the salt mix in the tank for 4 days and then did a 100% water change with fresh water and cleaned down all the filter and poured water over the background with a jug to wash off any salt residue, I also went around the tank with a cloth on the inside wiping all the glass and trying to get rid of any salty water left over. And naturally replaced the filter wool.

The yellow tinge is because f the bogwood leaching into the water

The yellow tinge is because f the bogwood leaching into the water

The yellow tinge is because f the bogwood leaching into the water

The ph at this point was around 8.2…woooohhoo getting there!!

2 days later I emptied the tank, I decided to double check all the seems and joins and make sure everything fits fine, I noticed a loose piece of rock (back left small piece if anyone is interested) so I decided to re silicon that. Once that had hardened I refilled the tank again..and replaced the filter wool

the tank kept a steady ph of 8.0 at this point!!

I added some sand to the tank and replaced the filter wool. Again…I noticed that the filter wool this time was a more brown colour, possibly the bogwood? I did a 30% water change, and the ph dropped to a steady 7.8!!!! and has not altered since that reading

with sand, ph 7.8

and that as they say is that, the background was no longer leeching into the water, the ph was steady and everything was secured down nice and sturdy, the filter/heater were both working fine and my attention could turn to the finishing touches. Such as the hood, lighting etc.

here are the finished pictures.

Unfortunately the background looks lighter in these pictures then it is in person, but you get the idea.

I have thoroughly enjoyed this project, It was far easier then I thought it would be and 10X more fun then I expected it to be, the hardest part was being patent with it and waiting in between water changes and not rushing any stages. I can’t wait to do the next one!! But I need a bigger tank first, lol 4ftX2ft I think… The possibilities are endless!
Last edited:

red devil

AC Members
Jan 7, 2003
Shenzhen, China
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Cool! Thanks for the blow by blow. I am inspired to continue with my project now...i am looking for the tank now. I am wondering if there is any way to add a coloring agent to the cement? I think if you could have added a little black to the very inner part of joints and cracks the tank would have a little more 3 d feel...also if you used a brush and sprinkled a little black - really fine dots - on the rocks would also have added more depth. Thanks again! The article has really helped me.


...and over the edge.
Staff member
Dec 30, 2005
Real Name
Mr. Normal
Nice build thread!


AC Members
Original poster
Feb 17, 2007
Hull, Yorkshire, England
I am wondering if there is any way to add a coloring agent to the cement? I think if you could have added a little black to the very inner part of joints and cracks the tank would have a little more 3 d feel...also if you used a brush and sprinkled a little black - really fine dots - on the rocks would also have added more depth. Thanks again! The article has really helped me.
doh ! i should have added this part, i considered useing pigment to the cement or even adding coloured aquarium sand into the mix to give some more coloured texture, i have seen a few background do this and it looks ace, but after 3 or 4 months the algae buildup covers most of the colouring details and replaces it with a really nice natural colouration....i am hoping it does that in mine! it is a bit of a gamble because if it doesent then i will regret not doing any more detailing work but i have only had this background setup now for a week or so and i have been leaving the light on for around 15hrs per day and already the background has an a slight algae buildup near the side which is spreading so i am very hopeful.

i think it is a great idea though especially the darkened cement near the cracks to give a depth feel. you also have to take into account the shadowing factor as well, most of the cracks and caves give a really cool shadowing across the background giving a lot more depth to the feel of the tank. but i would say that if you can get the cement pigment near you (something i struggled with) and you have the time to do it then defenatly go for it!


AC Members
Feb 27, 2007
excellent write up... i think i may well give this a go... your tank looks stunning and i realy like the sand you have used, excellent work Bahney