Introduction: Aquarium 3D Background With Cement and Thermocol(Styrofoam)

I planned to make a Aquarium Background following the instructions from by "rheta.erts". I found this project one of the best described.

However, my first attempt was a Failure. The issue was material used. I am in India and I could not found "ready to use concrete" and "high density Styrofoam". After putting a lot of efforts, the made background was floating and Silicone was not able to hold it. Then I re-planned everything and my second attempt was a Success. It's been around 6 months after installing aquarium background and it is working excellent with freshwater fishes and turtles.

So I thought of putting my project experience at this excellent platform with my motto -

"Yes, the aquarium background can be made with normal Portland-Cement and any low density Styrofoam" (Styrofoam commonly a.k.a. Thermocol in India)

This project might take around 2 months time to complete. So have patience ..

Step 1: Materials and Tools

  1. Cement (Portland or Concrete Mix) - 10Kg w.r.t. 48 US Gallons Tank
  2. Cement Colors (Red Oxide, Yellow Oxide) - 200gms
  3. Binding Wires (for cement strength) - 250gms
  4. Styrofoam (High Density) and Styrofoam pieces (discarded once can be used) - 2 sheets (Depending on design and background size)
  5. Toothpicks (Big and Small)- 1 box each (50 pieces)
  6. Knife ()
  7. Silicone Adhesive (100%, Underwater usage and Non-Toxic)- 1 Tube
  8. Silicone Gun - 1
  9. Plastic Mesh - 1 sheet 3feetX2feet (Depending on design and background size)
  10. Paint Brush - 2 (1/2 inch and 3 inch)
  11. Plier -1
  12. Gasoline - 200ml (Petrol)
  13. Gloves
  14. Water sprayer

Cement is used to make the background heavy enough to just sink in aquarium water. Rough sand can also be mixed along with cement.

Silicone Adhesive is used to fill the gaps, once background is put inside aquarium. The Styrofoam design pieces are also glued using silicone. I used GE-Silicone 2000.

Styrofoam is used to create structural design and carvings.

Gasoline is helpful to melt the Styrofoam.

Step 2: Plan Ahead

It is very important to plan ahead for few things.

Selecting Design: browse on internet to get ideas. Your imagination is the limit.

Selecting Aquarium: I suggest to select a decent size (35 Gal+) aquarium for this project. The old and used aquarium is a better option.

The cement/concrete makes the water basic (High pH). The cement needs to be cured before putting fish in aquarium. So once the background is placed in the aquarium, it needs to be cured for at least 2-4 weeks. If you already got the fishes then shift them to a separate aquarium.

Mark the places for Filter, Bio-Material, Heater, Air-Tube, Light etc..

Design, keeping in mind Water-Flow, size of fish, hiding places, cleaning etc..

Do not just rely on measurement and imagination, keep placing the design in empty-aquarium to check the dimensions and the look during project execution.

You can also embed PVC pipes, Air tubing etc. in structure, if you like.

The Heavy-Background need to be placed very carefully into the aquarium to avoid breaking it. Glass can sustain a lot of weight so don't worry about - how heavy?

Step 3: Layout

Cut the sheet as per aquarium background size. I decided for L-shaped (2-sided) background design. The third side is kept open.

Mark the planned embossed designs, margin for filter, heater, air tube, bio-material etc.. Name the marks as R1, R2, F1, F2 etc. Marking helps in identifying carved objects later and placing it at correct place.

Attach the raw-crafted pieces using toothpicks, bamboo skewers. Place the attached design in aquarium to check dimensions, look, lighting and fitting of equipment.

Step 4: Crafting

During layout design, we have got a fair idea about the appearance. Keeping that in mind, start carving Styrofoam. Keep looking at natural rock images for natural appearance.

I liked the stacked stones, slate rocks, grooves, so I combined all of them in this design.

I carved the embossed designs and pinned it at background layout sheet using toothpicks and bamboo skewers.

Don't go for very fine carvings as cement layer is going to cover it. Go for a deeper texture, keeping in mind about the cement layer thickness.

Don't make very fragile designs as while putting cement layer it might break.

Don't make smaller holes as small fish might stuck inside. Also cleaning might be tough.

Random patterns, cuts looks good.

Don't throw away the cut pieces of Styrofoam as that might be useful later.

For larger or complex designs, glue the carved Styrofoam pieces together using silicone. Attach them using toothpicks.

The base of the crafted embossed items should have larger surface area. It is better to be tapered down towards top. This helps while attaching items to base background sheet. The cement layer will add weight at the top corner. It might tilt it down.

Tip: You can use water spray if the wasted Styrofoam started flying everywhere.

Step 5: Assembly

Crafted design pieces need to be assembled now.

We have already marked the components with labels R1, R2 ..F1, F2 etc. at Layout step.

Start from base and reach towards top to attach crafted design items with background sheet.

You might need to apply silicone at back of the crafted piece and attach it. After that pin it using toothpicks or bamboo skewers depending on required size.

Keep a little space between embossed items as later while applying cement layer, the brush with your hand could reach there. I had used small brush (actually shaving brush) to reach out narrow places at cementing stage.

The L shape (2 sided) assembly is better as the background could stand on its own. I had placed a triangular sheet at the corner for strength and stability.(check in pics)

Put the assembled design into aquarium and check fittings, appearance etc. If possible check with filter, heater, light and other items placed.

If the items are firmly attached you can further refine the design using knife or blade.

I have inserted cut wires about 3 to 4 inches on Styrofoam as this provides concrete layers better strength. Make a staple |____| kind of shape and insert the wire at multiple places in design pieces. Put bigger wires at boundary and corners. These places need strength as you hold it while moving the background structure.

Step 6: Build

Now, It's time to start building the background using cement.

At this moment, we need to very careful as Styrofoam does not have great strength to hold cement weight. Please pay extra care while moving or tilting the assembled structure.

Also at this point, people have different approaches to build (from internet).


  1. You can actually glue the design using silicone to the aquarium. Paste the protective sheets at rest of the aquarium walls to protect it from cement spill or color spill. I have not opted for this approach. My empty-aquarium was placed at drawing room, so I could not work there. The cement layer need to be dried in open area so I will not be able keep moving aquarium in-out.
  2. You can build the design first and leave the backside of background untouched. Once the background is ready, you can apply silicone at back and put it inside the aquarium. I felt this is less risky and it proved to be lucky decision for me.
  3. You can split the design into 2-3 parts and assemble it once again after build. I believed it was more cumbersome.
  4. There could be other ways which you can better think off :-)

So I selected approach-2 as I will build the background and place it in aquarium after completion.


Lay paper, plastic or old cloth sheets at the floor as cement spill is unavoidable if you are not professional.

Lay the assembled structure at the floor.

Prepare cement mixture. Wear protective gears for eyes, nose, mouth and hands as cement dust can enter. Plan to apply 1 Kg of cement at a time. Take the cement in a bucket and add a little water. Wait for the cement to absorb the water. Add a little more water and let it absorb again. When complete cement turned to dark color then add little water and mix till Honey kind of runny mixture is prepared.

Start applying cement mixture to structure using brush. Keep water sprayer or a jug of water nearby to apply if the brush gets cement lumps. Take a small quantity of cement at the tip of the brush and apply as a layer on the design.

You need to achieve a layer of approximately 3-5mm.

Let the cement layer slowly dry under the shadow for 1 day. Keep sprinkling water time after time otherwise the cement layer will start building cracks.

If the cement layer is completely dry then check the strength by pushing a corner with your finger. If it is getting broken then it has not gained the strength.

Apply one more layer 2-4mm of cement on day 2. Apply a thick layer of cement at the boundaries for greater strength. Let it dry for one more day under shadow. Again, keep sprinkling water time after time.

Once the structure is completely dry, sprinkle water and let it dry in direct sunlight for a day. Again, keep sprinkling water time after time.

Once it is dry and has enough strength then it is time to test it's bouncy in water. Once this test is passed, you can go for color or directly place it in aquarium if you like.

I would say it's a last mile ...

Step 7: Structure Buoyancy Test and Modifications (in Case of Floating Issue)

It is a very important to test your background structure at this step. As your aquarium background project might need different approach from here onward.

Buoyancy Test:

  1. Fill the water in large container or your aquarium itself.
  2. Put the aquarium background structure into water at vertical position or in the position you want to place it in aquarium.
  3. The structure must sink to minimum 80%. In other words 80% of the structure volume should submerge into water. If it is more than that, it is great.

Why 80% or higher?

I would personally say 100% structure should be submerged. Because my experience gone bad.

Reason: The silicon and Styrofoam has limited strength to hold the structure submerged in water because of buoyancy force. The Styrofoam has generally 60% to 90+% air. It makes this kind of design a high-volume, less-weight kind of structure. So either Styrofoam will break-off or silicone will break-off eventually. Even if you put the cement at backside of background and glue it using silicone, it might come of because of constant buoyancy force.

Believe me buoyancy force is very strong! My background structure submerged only 20% and I was not able to hold it under water with force!

So now if your designed structure passed the buoyancy test, then congratulations ! You can move to color step or placement step.

If the designed structure failed the buoyancy test, then don't worry, project is not doomed. We will do modifications in the structure design and let it clear the buoyancy test ! Believe me ! I have done that.

Buoyancy test Passed: Move to color step/placement step

Buoyancy test Failed: Stay with me ...

We need to plan for increasing the weight of the structure. Once the weight-volume ration is established the structure is ready. I am going to melt the Styrofoam portions of design from backside and fill it with Cement-Sand-Styrofoam balls mixture. (Sand optional)

For the next few steps you need to focus more on text guidelines vs pictures.

Step 8: Modified Layout

If the structure has buoyancy issue then we need to increase its weight.

While increasing the weight by filling cement-sand-foam mixture make sure the weight distribution of the structure is uniform. If one part become heavier than the other then it might break while lifting.

Here I have identified two approaches -

  1. Increase the weight at selective parts of background.
  2. Make a new backside of structure, made of concrete and attach the structure to it.

I started following approach-1 but I mishandled the design and embossed designs broke. Then I followed approach-2. I believe both approaches are fine. Approach 2 is little complex that 1. So I would suggest to go for 1.

Follow the text more than pictures.

Approach 1:

Mark the backside of embossed carved-designs as vertical and horizontal rectangles. Mark the corners and boundary of the design about 2+ inches (more is better). Leave Styrofoam in between as it will help to level while cementing.

Approach 2:

Take a plastic mesh sheet same as the size of background. I have marked the sheet in three parts. For L-shaped design, lower bottom part, left vertical part, middle vertical part. For me it was approx. 7inchX24inch, 7inchX24inch and 24inchX24inch.

Cut the mesh at lower bottom part to fold it later into background shape.

Step 9: Build Once Again

Here we are re-building the backside of the background structure as front part should be intact.

Approach One:

  1. Take some gasoline (petrol) approx. 100-200ml in a bowl. Take a brush and start putting on marked places. The gasoline immediately starts dissolving the Styrofoam. Do not pour the gasoline as it might dissolve complete Styrofoam in design. Apply small amount from brush and wait for dissolving.
  2. Dissolve the embossed design's visible Styrofoam from backside. It will convert in a Mold. Dissolve only marked places.
  3. Prepare a mixture of cement and Styrofoam balls. Rub the Styrofoam pieces together and balls will get separated. Collect them in a bucket. Sprinkle water over balls if the balls start flying. Add cement in the bucket. Add water and let cement absorb it. Make a uniform mixture with density like honey.
  4. Pour this mixture into the molds gradually and in small quantities. You can use stick to push the cement-mixture deep in the corners.
  5. Do not fill the molds completely on day-1 as large weight can break the design. Do the things gradually and in small steps. Plan for at least 3 days to completely fill the molds and let the cement-mixture get dried and gain strength.
  6. Once the molds are almost filled, add a layer of cement-water mixture on top of it. Level it using brush or plastic card at untouched Styrofoam level.
  7. Let it dry one more day or two to gain strength.
  8. I hope you are already wearing protective gears, gloves etc. while doing this.
  9. Once design is completely dried and has good strength then it is time for one more buoyancy test.
  10. If buoyancy test is passed go for color or placement step.
  11. If buoyancy test is failed again then you might have to dissolve the remaining Styrofoam (unmarked for level) and repeat this process.

Approach Two:

  1. Spread the plastic mesh sheet on flat surface. Place a plastic sheet underneath as cement might stick to the floor through the mesh.
  2. Mark the boundaries of background on the sheet.
  3. Prepare a mixture of Cement and Styrofoam balls. Collect the Styrofoam balls into a bucket and sprinkle water over it. Add cement and a little water. Let the cement absorb it. Make a mixture of thickness similar to honey. Styrofoam balls can be obtained from Styrofoam pieces while rubbing them against each other.
  4. Spread a thick 5mm+ layer of cement mixture at the three marked parts of plastic mesh sheet. Leave a gap around 1 Inch in between Bottom, Left and Center portions to allow the sheet to be folded later. Remember the sheet needs to be folded into Background backside shape once the cement is cured. (picture attached)
  5. Cut wires approx. 3-5inch and embed them into concrete. Put a array of wires in the corner so that it can be tied together once the sheet is folded.(picture attached)
  6. If the embossed design is broken or it is attached to background, dissolve the complete Styrofoam using gasoline as mentioned in Approach one. Create molds out of embossed designs.
  7. Prepare the cement and Styrofoam balls mixture and pour into molds as mentioned in Approach One.
  8. Let the Cement layer at sheet and molds dry for 2 days to get strength.
  9. Prepare a cement-water mixture and attach the filled-molds to desired places. You can also put cement at backside of background structure and attach it to the sheet. I have included a picture that depicts how I attached the molds to cement layer at sheet.
  10. Let the structure dry for 1 or 2 days to get strength. Keep sprinkling water so that cracks are not developed.
  11. Now let us fold the sheet to make a L-shaped background. Lift the Center and Left portion to vertical state. Tie the visible array of wires together to make this structure steady. Maintain the angles at 90 degrees as it need to be fitted into aquarium.
  12. Bend the visible wires inside and put one more layer of cement water mixture on visible wires. Cement should cover the wires and joints.
  13. Let the structure dry for 2 days. Keep sprinkling water time after time.
  14. Once the structure is completely dried and has good strength then do the buoyancy test one more time.
  15. The buoyancy test should be cleared as the structure is almost made of concrete and heavy enough.
  16. It is time for color or placement step.
  17. I hope you were wearing protective gears.

Step 10: Color

I have used non-toxic cement oxide colors.

The inspiration is taken from some Japanese rock garden pictures.

We need to think about the resultant color when the cement and oxide pigment color are mixed.

The Cement is of Grey/Metal color. If small yellow oxide pigment is added it will be turned into greenish-yellow color.

If red oxide pigment is added then it will turn brown color.

You can find the online tools that can define the resultant color if 90% grey and 10% yellow is mixed.

Required items:

One 3 inch painting brush, one small brush to reach-out deep corners and a toothbrush to sprinkle color are required for similar texture in pictures.

Prepare multiple colors of your choice with different gradients.

Dark Yellow: 3:1 ration of Cement and Yellow oxide

Greenish Yellow: 8:1 of Cement and Yellow oxide

Red: 3:1 ration of Cement and Red oxide

Brown: 5:1 ratio of Cement and (Red oxide + Yellow oxide)

This is more of a trial and error method to get desired colors.

I first applied a dark color at bottom (lower portion). Then applied different Greenish Yellow combinations as a gradient from bottom to top.

Let these base layers dry for one day and keep sprinkling water time after time.

Take a toothbrush and dip into Dark Brown or desired color. Sprinkle the color at desired place using thumb. I hope you might already know the method. Put the thumb on colored bristles, pull it and then release tensed bristles towards the target place.

You can try different colors as you can anyway put another layer of color if you don't like it.

Let the colors dry for 2 days. Keep sprinkling water time after time.

Once dry, your background structure is ready to be placed into aquarium.

Step 11: Placement

I guess, it took around a month to reach this stage. Phew !!!

Place the Styrofoam sheets at the back of aquarium glass if the backside of your structure is not flat. Also you can remove them later once the background structure is placed as this is for additional safety. I have let the structure sit on a thin sheet of Styrofoam. I believe it's a must as a small bulge portion at the bottom or sides can cause the aquarium glass break.

If the structure is too heavy and you think it might slip from hand while putting into aquarium. Then glue the Styrofoam sheet to the bottom of aquarium. Then fill it with water to 70% level. Put the design into the aquarium and let it sink. The weight of the structure inside the water will be very less.

I was able to put the background structure at the Styrofoam sheets without filling water.

There might be imperfections at the corners or boundaries. I filled the gaps using Styrofoam. Then I applied Silicone at all boundaries, gaps and at required places. This will block the water going inside the gaps.

We are just one step away from completion ..

Step 12: Curing and Stablizing PH

The structure is made of cement so the curing is a must step.

Curing by definition is settling of concrete.

Let us make the concrete structure safe for fresh water aquarium creatures.

Cement structure, when placed in water then some of it's components dissolve into water and make it basic (High pH). This process gets stopped after some time. To stabilize the pH we need to give the chemical process some time and environment.

I followed these steps as mentioned at several web forums to stabilize pH.

  1. Fill the aquarium having background structure with water. Little acidic water is preferred. Leave it for 2-3 days.
  2. Do 50%-100% water change everyday for 2-3 days.
  3. After first week keep doing 20-30% water change every day for the next week.
  4. Do 100% water change this day.
  5. Keep monitoring pH levels every day for variation.
  6. If pH variation is observed then do 20-30% water change next week and observe pH change.
  7. If the pH variation is not significant then the aquarium is ready to start for Nitrogen Cycle.
  8. Place the bio-bacteria and ammonia to kick-start Nitrogen Cycle.
  9. Put filter, heater, bio media etc..
  10. Put some fishes and observe them for some days.

Your aquarium with new DIY background structure is ready to welcome inhabitants !

Congratulations !!