Making our own aquarium PU background

Report of a ABCV DIY event performed by Frans Druyts and Johan Thijssen.


Question: What looks duller than a bare aquarium with all technical equipment visible? You've indeed guessed it right, nothing! A setup like this just fails to inspire the real enthusiast and what's worse, the cichlids won't like it either!

What can we do then to build our own decently aquascaped tank? We could make a small effort and paint the back (of course on the outside) of the aquarium light blue, what could make the cichlids feel a bit more comfortable. The disadvantage is that this makes the tank look like an ordinary commercial shop tank. Dark (grey-brown) paint is one step further in the good direction. Prefab PU foam sheets will look even better and enable you to create comfortable dark hiding spots in the back of the aquarium, but although the ugly technical equipment don't attract attention against such a dark background, it still remains visible! Of course a huge setup of large rocks can be used to hide the most disturbing elements, but there is a better solution: Non-toxic 2-component PU foam!!!

Non-toxic 2-component PU foam is a very good material to build a 3D background. Although it doesn't look as neat & real as the "Back to nature" background, it does a fantastic job at a very reasonable price, and it can be custom fit in all existing aquariums. With your own imagination as a guide, you can create a very nice looking background with all filtration, hiding and heating elements built in! Also wood branches can be attached in the background, what gives a very realistic effect in new world cichlid tanks. BTW this material is also marine proof!

The principle is rather simple: The chemical reaction will produce heat that will cause a specific (3rd) chemical to cook. The tiny gas bubbles that arise causes the mass to swell. When the chemical reaction is complete a closed-celled foam is formed.

There is one WARNING though: Clumsy persons are advised not to try this DIY project, as the 2 components are very sticky when they're finally mixed together, and the project could end up in a gaint mess!


A background built-in in an existing plywood tank


What PU do we need to make a background like this?

Probably the biggest problem is the worldwide availability and the difference in commercial names (Hmmm sounds familiar, ain't it?) , but we simply need the 2 separate components, and not the product out of a spray can because we must add dyes during the mixing. Straight out of a spray can the PU looks pale yellow, what's not exactly a natural color. Make sure to search after NON-TOXIC 2-component PU. Here in Belgium this product (resinol270 and urestyl10) is available in a specialized polyester shop.

What else do we need?

  • Very important: A second person ( to help with the mixing).

  • Solid plastic mixing (about 250ml) cups that can be deformed without breaking.

  • Small plastic measuring cups for dosing equal quantities of product (the containers from 35mm photo film are ideal)

  • Wooden mixing sticks (for mixing of course)

  • Oil paint & syringe (to add drops of colouring matters to the PU mixture - can also be mixed with one of the components before mixing; what gives a uniform coloured background = less attractive)

  • Top coat (epoxy paint) & Paint brush (to apply the epoxy paint)

  • Acetone (for cleaning)

  • Gloves (to protect your hands)

  • Pieces of glass (to keep the background in place)

  • Large PVC tubes, pieces of polystyrene foam, wooden branches. (they can be moulded in to create caves and 3D structures

  • Large plastic foil (to protect the worktable from spills)


Where will we make the background?

Before we rush into the mixing of the PU,  we will choose where we want to make the background. It seems logical that it's moulded into the tank, but sometimes this isn't possible. When a tank can't be moved, it's wise to mould the background in a similar sized wooden frame with a plastic bottom. When the construction is ready, it can be cut out of the frame (the plastic is easy removable), cut in 2 and glued  in it's place in the tank with silicones. The joints can be finished with a fresh amount of PU mixture. When we mould the background straight into the tank, it's advisable to glue T-shaped glass pieces to the back window to prevent the structure from breaking loose.


The back of the tank ready: the surface sanded & degreased and the T-shaped glass pieces glued with silicones will ensure a good attachment of the background!

How will we work?

To avoid mistakes all recipients are marked with coloured tape or a felt-tip. After all we wouldn't want the chemical reaction already starting in the measuring cups. Take 1 cup of both components, add some drops of the oil paint, mix very well and pour out the mass in it's place. The mass will expand and will cover all protrusions. When adding several layers you can hide filter compartments, air tubes tubes. Also PVC pipes can be moulded in to create caves. Take care not to create traps where cichlids can get locked in with a waterchange! Wooden branches can be fastened in the stiffening mass. As you see there are a lot of options and your own imagination will be the only limit to creaty a magnificently looking 3D background


The 2 cans ready for use & Johan measuring a certain quantity


Johan pouring the 2 components together & mixing the beaker

The finishing touch

After the background got ready we will add a protective layer. In this project the transparant G4 (some kind of epoxy paint) is applied with a brush. A small bit of green paint can be added to imitate algue growth.


Frans pouring the mixture in it's place & modelling the mass


Frans standing in front of his creation! This will become one of the many show tanks on the next ABCV show

Enjoying the result!

Hopefully everything became a succes, and after some waterchanges to be absolutely sure no chemicals will be left in the water, we can start cycling the tank and finally adding our first fish, so we can start enjoying our own creation!

Much success!

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