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    3D Polyurethane Foam Background


    FAQ - Read the frequently asked questions about "3D Background".

In the African cichlid breeding many of the fish keepers are not satisfied only with one-colour background of an aquarium so that they buy some of the commercially offered products imitating the African lakes environment. These backgrounds are mostly plastic or laminated casting. Many of them are very good, however, they are not always available for everybody and often are expensive. Those are the reasons why skilful fish keepers are trying to make some similar background or also better looking one and cheaper. There are many technologies and materials useable for this purpose and it depends on one’s skills.

I had decided to make the polyurethane (PU) background after the study of a very few sources in 2001. The background described here was made in 2001 and is not used more. The main reason for this was that the 250 litre tank, in which the background was installed started to be too small for me and I set up a new, bigger aquarium with a new background. I innovated the method of building the background and used other materials. I’m sorry that I’m not able to illustrate the building of the PU background step-by-step on the pictures but in the time of its building I did not own the digital camera so the pictures come from year 2002. I know about some mistakes I made and found some tricks highlighted in the following text. Let’s go from the beginning.

Material preparation and making the background base

I had used 2 cm thick polystyrene board as a base of the background. It is possible to use other materials sure, i.e. thinner plastic board but the polystyrene seems better to me because it can be easily treated, it is compressible and light. The disadvantage is that it is full of air and therefore swimming in the water.

Warning! After the PU foam was sprayed and hardened, the central part of the polystyrene board bellied in toward the front. The PU foam deforms the polystyrene board and it cannot be attached close to the aquarium back wall. The solution is at the end of this article.

I had cut the polystyrene board by the aquarium back wall dimensions to fit between the side walls and horizontal brace accurately. The background can be used for hiding all the technics (heater, sucking pipe of the canister filter etc.). For this purpose, I made some stack from the L-shaped polystyrene which is the part of the background in the left corner. I placed also an internal filter to this stack. At the base of the stack, the hole is cut which serves for water input to the filter or sucking pipe. In the upper part of the stack, there is a hole through which the filtered water flows back to the main part of an aquarium. Everything is visible in the pictures.

TIP: During the building another backgrounds I have found that if the complete background will then be glued to the glass (back wall of the tank), it is needless to make it out of the tank spreading the PU foam on the polystyrene board. The polystyrene can be missed and the PU may be spread directly on the glass. PU foam is sticked on the glass firmly but can be removed easily if needed. The only disadvantage is the limited space in the tank when making the background directly in it. Aquarium must lie at the back wall while making the background, otherwise the fresh foam drops out. During the work, a waste (sand, small parts of the foam) increases and is everywhere, so building the background in the room is often a nightmare for the family :-)

I continued with spreading the foam on the whole polystyrene surface and also on the polystyrene stack. After the first layer dried, I applied the foam on some places the next layer. It depends on the planed final look of the background because it is possible to create thicker background with many crevices and caves but also thinner flat one imitating the stone surface. I would like to suggest that the volume of the sprayed foam depends on the force when pushing the valve. If the valve is pushed strongly, the foam will be extensive after drying and It can’t be always suitable. In that case, the foam contains more gas bubbles and seems fluffy. If the valve is pushed firmly and slowly, the foam will be harder and more compact with a few cavities. It is often not cured inside and is sticky.

TIP: I have been often asked which kind of foam was used. It doesn’t matter. Any white or yellowish foam is fine but not blue or blue-green. This kind of foam colorizes the water blue-green. I bought that foam by mistake and even it was used only minimally, it took some time until stopped to release the colour. It is not needed to buy some special, i.e. antifreezing foam. The cheaper, the better. I have used the Ceresit foam and I’m very satisfied with it. The silicone should be intended for aquarium use, no mater which brand. I have used the Ceresit silicone.

Warning! Take care while working with the foam because it is very sticky after the spraying and can’t be removed from clothes. It can be removed from the hands more easily. If you will smudge your hands, leave the foam as it is, don’t wipe it from the hands immediately but after it dries. Then it can be scaled of the hands easily. It is the same for the glass.

Creating the background shape

This part of the work is hardest but the finished look of the background depends just on it. I had not good technique from the beginning and tried to cut the foam by knife but the result wasn’t as expected. My idea was to copy the shape of the rocks I had in the tank which were full of holes and cavities. It can’t be done by knife. I have found that the best equipment for doing the holes in the dry foam is a middle-sized tweezers. I tailed small parts from the foam continuously and the background started to look like mentioned rocks. By that way of work, you never can damage it because you are continuing gradually and the work can be adjusted anytime. You can still add the foam if you wish. I tailed bigger areas on some parts and doing that the bigger hole (cave) raised. The background was 10 cm thick at some sites so there were many possibilities to shape it.

A surface adjustment

It’s clear that the foam surface needs to be adjusted to strengthen it and to protect it from the water soaking. Again, there are many possibilities. Some of the aquarists use the epoxy resins. Formerly, I also thought about the Epoxy 1200 resin but at the package, there was stated that it is toxic for the aquatic animals and causes the reproduction damage. Although many of the fish keepers used this method successfully, I drop the matter. I had decided to use the transparent silicone. The background was then thoroughly coated with the silicone. Don’t coat the whole background at once but only by small parts and sand it immediately while the silicone is wet. The sand must be pressed into the silicone. Put more sand than needed and simply press it by your palm to the silicone. An excess sand can be then shaked or vacuumed from the background. You can use also sand of a various colour (I mean a natural sand, i.e. yellowish, brownish, grey, white, black) and imitate the natural look of the rocks. Avoid the strong contrasts between the sand colour as the background would look artificially. When all the background is covered with the silicone and sanded, leave the silicone dry at least for 24 hours. Then vacuum sand not glued and repeat all the process. Try to cover every piece of silicone by sand to be not bare because it would disturb the whole effect. Algae will not cover it. It is needed to use at least two layers: silicone - sand - silicone – sand. The silicone must be dry before another layer is applied.

The final adjustment and installation into the tank

Before placing the background into the tank, remove all the excess sand from it, shower it and leave to dry well. A background installation alone depends on the way of fixation in the tank. Formerly I fixed it between the horizontal brace and the bottom. The background has tried to pop up and nearly ripped the horizontal brace. The lower part of the background tries to rise to the front glass. I had the background in the tank about a year fixed this way. The bottom part was lined by sand and some rocks which fixed the background. It looked like a natural reef. In spite of that the background bottom has moved from the back glass about 2-3 cm. The fishes swam into this space and the detritus accumulated here. That was the reason I drained the tank, removed the background, dried back side of the background and back wall of the tank. I had siliconed the whole aquarium back glass (2 pcs for 100 x 50 cm glass) and glued the background for ever. The problems with background popping up have ended forever and silicone fixed background provided me with the more option to create an aquarium interior as the rocks need not be leant on the background. It was unpractical mainly during the tank cleaning when the rocks were moved and the background tried to move forward. It was not easy to put the background back in the tank full of water. I hope that many of the enthusiasts are inspired by this DIY plan. If some parts of the background building described here are unclear, don’t hesitate to contact me. A few aquarium pictures with the background is shown in this aquarium description. Another kinds of the backgrounds made of the real rocks will be described in the next part.

Warning! In spite of the surface adjustment, the background is delicate and can be damaged by the sharp rocks.

Obr. 3 – Akvárium s PU pozadím Obr. 4 – PU pozadie v akváriu - detail Obr. 5 – Akvárium s PU pozadím - večerné osvetlenie

    FAQ - Read the frequently asked questions about "3D Background".

DISCLAIMER: By building this DIY project you agree not to hold the author responsible for any injury or bodily harm you may cause to yourself or others. Read all safety instructions pertaining to equipment prior to use.

Copyright © 2003 - 2017 Robert Toman




Description of my aquariums, breeding history, photos and everything that happened in each tank during the time.


Tips and tricks for doing a various tools and equipment for fish keeping. Here, you will find an inspiration for your own attempts to simplify the fish keeping.


My own experience with African cichlids breeding. A detailed description of fish keeping and breeding with special things I found during the years of fish keeping.



My own photos anf videos of fish kept in my tanks.

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