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How to build a plywood fiberglass tank Part 2

Finally, we are talking about the construction of our wooden and fiberglass aquarium.

For those who have not read the first part here is the article “How to Build a Wood and Fiberglass Aquarium Part 1“.

In this article we will discuss the construction of the reinforcement curbs and how to apply the resin.

The first thing to do is get everything you need.

Lightweight fiberglass cloth (300gr./sq. m.), resin (read below) and catalyst, aerosil (colloidal silica), 3/4 brushes of 40mm, a fairly accurate scale, some small plastic containers to weigh the resin, scissors, gloves, protective suit and mask to prevent inhaling such a toxic product. It is better to have also carpenter stands. Also get the sandpaper.


What type and how much resin?

Concerning the resin, it is important to make an important distinction. You can use the polyester resin and lastly an epoxy resin coat to waterproof everything or just epoxy for the whole process. I used only the latter, but I do not advise because actually the polyester is really much cheaper.

For the amount of resin and cloth I recommend following the instructions on the product datasheet according to the size of your tank. Consider that at least 3 coats of both should be applied.

Before buying everything, some considerations have to be made. You have to work in a very airy place, better outside. The temperature must be 25 degrees, so wait for spring or summer, but it is not advisable to do so in late autumn or winter, but of course it also depends on where you live.

Be sure to read everything until the end, before buying the material and proceeding with the construction.


Resina and aerosil preparation – photo by Simone Grimaldi –

Preparation of wood

First, give a quick sanding inside the tank, everywhere, with sandpaper and make the holes, for the overflow and return, where you prefer them. I used an adjustable circle hole cutter for my drill, so I could easily make all holes, both 50mm and 40mm, using a single tool. However, the hole saw is also good.

With a vacuum cleaner, clean all the tank from the sawdust.


Photo by Simone Grimaldi

Making of the curbs

With the help of someone, we position the tank on the ground, placing it, however, at 45 degrees, ie leaning on, for example, a wall. Let’s make sure it is stable and it can not fall and very important protect you with gloves, mask and suit. Do it whenever you are working with the resin!

We pour about 300/400 grams of polyester resin into the plastic container and then its catalyst. Read the instructions on the container, surely it tells you what percentage you have to apply it. Generally the catalyst or curing agent is 2% when using polyester resin, while it is 45% for epoxy resin, but each product may be different and we will only use epoxy for the final coat. Mix the two sides well and finally add a tablespoon of aerosil and mix again. You need to add aerosil until the resin has gained the consistency of honey, more or less. This product makes the curb resin tough as the stone and attaching itself to the wood will create a protection for both the water out of the corners and above all the tank will become very strong at the pressure of the water!


Photo by Simone Grimaldi

Now start pouring the resin on the corner we put on the ground, so that it will create a curb inside. The curb must have a depth of about 3/4 cm, so if the resin is not enough to fill it all prepare the other. Finally, wait until the resin is dry before moving the tank and proceed. It’s best to wait a full day before moving it. I did the mistake of move it when it looked dry, but after a few hours it’s all gone !! So do a curb every day, at most two, but make sure it’s tough.


Photo by Simone Grimaldi

First coat of resin

Finally here we are! It’s time to apply the resin!

We put the tank on the stands and make sure it’s bubble. As already said, protect yourself with gloves, etc.

Let’s start by pouring a small amount of polyester resin, for example 200 grams into the container and then immediately after its catalyst. I do not advise you to do it all together, because you surely risk being dried in the container, then small doses at a time, until you have an idea of ​​how much it serves for each panel. With a wooden stick we mix everything. This time the aerosil is not used. Let’s apply the first coat of just resin, without the cloth, then spread it all the way with a brush across all panels and curbs, evenly, ensuring that you do not leave empty spaces. Note that the resin runs down slowly from the vertical walls, then apply little and if necessary repeat. Alternatively, you can make a panel at a time, each time turning the tank so that the panel to be treated is always the bottom one.

Let it dry for a few hours.


Fiberglass cloth coating

Before starting this phase, I make an important premise. The edge of the frame that will be in contact with the silicone, for bonding the glass, must be resin without using the cloth! Resin only.

Now prepare some more resin as before, in small doses, even if you now already have an idea of ​​how much it needs, since you’ve already done it before!

Let’s start by cutting out several squares of fiberglass cloth, about 30 cm x 30 cm. Now choose a corner and start spreading over the resin with the brush for a slightly larger area of ​​the piece of cloth we cut before and before the resin gets dry stick over the cloth, crossing it between the two panels forming the corner . At this point, brush the resin and start tapping (never brush over the cloth !!) over the cloth with the tip of the brush. If you brush the cloth, it will stick to the brush, so that’s why we tap it. The resin should be tapped until the cloth is completely soaked. It is understood by the color changes.

In practice, this process has to be repeated until the entire tank is internally covered by the impregnated resin cloth. First all the corners and then the rest of the tank are made, reminding us to always poke all the pieces of tank on each other and never side by side. Let’s say it’s enough to overlap them for about 5/6 cm. It is not difficult, in the end it is a simple repetitive operation that can be summarized as follows: apply the resin, lay the cloth over it, and finally reapply resin over the cloth.

Let the resin dry between one coat and the other, the ideal is one coat a day.

Note: It is not necessary to exaggerate with the amount of resin in a single coat, indeed … too much thickness often it likely can creep. Better apply more coat of resin + fabric. That’s the secret.



The fiberglass we created is of an ugly unwatchable color. Therefore, in the construction of my aquarium, I used a blue dye paste to apply on fiberglass.


Final waterproofing

After dyeing the interior of the tank we are ready for the final resin, which we will do this time with the only epoxy resin, a waterproof, non-toxic product once dry. It should be applied without fiberglass cloth, just as we did with the first hand, but to have some extra assurance that the tank is waterproof, I advise you to make a panel at a time, placing it first horizontally and letting the resin self-leveling on top, coating well even on the curbs. Then once dry, repeat for all the panels. If some resin remain … apply it everywhere as a last hand.

Even for this time we have finished and wish everyone a good job. Stay tuned for the next article, where we will glue the glass and test the waterproofness!


Appassionato di informatica ed elettronica sin dall'infanzia, sempre in deficit di conoscenza, ho trovato in questo affascinante universo dell'acquariofilia l'argomento che riesce a stimolarmi ma mai a saziarmi abbastanza da diventare noioso!

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