Methods of connecting hardscape

Modern aquascaping has a strong focus on the use of hardscape elements, and having ways to attach hardscape safely and efficiently allows complex hardscapes to be built quickly.

A few points on preparing wood & rock; for wood pieces that have bark that peels off easily, the bark should be removed so that the glue can contact the hard wood core directly. For rocks that are very dusty, removing excess rock dust may allow better contact for certain joining methods.

Gel super glue (gel cyanoacrylate)

Gel superglue is good for small joints. It cures faster than silicone, but does not fill gaps effectively, so a good contact area is necessary. A filler such as powdered aquasoil or wood chips can also be used to fill gaps. It takes a few minutes to cure. It will leave white stains on the hardscape if used underwater (it will also cure underwater, so it can be used to glue plants to hardscape in filled tanks).

Gel Super Glue is applied to two pieces of wood, but must be held in place for a few minutes to allow the glue to set. The glue is almost invisible after it is applied.

It takes another 5 to 15 minutes for the glue to harden enough to support weight. When the hard scape is disassembled, the residue is visible but small.

Gel Super Glue is good for connecting small pieces of hardscape that have good contact with other hardscape pieces. It is easy to hide and, if the contact is good, can support quite a bit of weight if left to cure completely. However, it is best used on pieces that rest on the hardscape, as the glue takes a few minutes to set (if the piece cannot support its own weight, you would need to hold it in place for a few minutes).

Smaller joints are made with super glue, while larger joints are made with liquid super glue and cigarette filters. The total construction time for this aquascape is less than an hour.

Gel superglue is also used to attach plants to hardscape. All of the plants on the hardscape in this picture were attached with Super Glue.

Kneadable epoxy / Epoxy putty

It comes in a paste made up of two different chemical components. It is then kneaded by hand into a soft putty that can be used to bond hardscape. It is very strong when cured - it hardens to the consistency of rock. However, it is best used on non-dusty hard scape surfaces, which can affect its adhesion. It is good for heavy duty work due to the strong bond. Because the paste itself is pliable and deforms to wrap around and fill in uneven pieces of hardscape, it can be used reliably even when the contact between two pieces of hardscape is poor; such as on porous rock or rough wood.

It does take some time to cure (although it can cure even when wet). The bond begins to cure in a few minutes after the two components are mixed. However, it takes about 10 minutes to set and longer to completely cure. If the joint is not carrying a lot of weight, it can be worked on after the initial hardening in 10 to 15 minutes.

The other disadvantage is that the epoxy leaves very obvious marks on the hardscape when removed. These can be chipped off with a Dremel or peeled off with a screwdriver. Epoxy can also be expensive to use in large quantities and requires more handling time (components must be kneaded for each joint just before use).

In general, this method produces strong joints, but it can be cumbersome to use throughout a hardscape project. I would reserve it for large joints where I want a strong bond, especially joints that need to support some weight. Several smaller joints would go faster with super glue.

There are some quality differences between brands, some brands are stickier and adhere better to porous/uneven surfaces.

Kneadable epoxy comes in tubes consisting of two compounds. Kneading them together to form a uniform mixture begins the bonding/curing process.

Due to its ability to fill gaps, uneven parts that are difficult to bond with gel superglue can be bonded with kneadable epoxy. The increased contact area provides a strong bond. It cures in a few minutes, so you'll need to hold the pieces together for some time if they don't hold on their own. It takes time (one hour) for the bond to fully cure to load bearing capacity.

Because it is a more obvious filler, it should be used at an angle that is hidden from view if possible - if not, it can be covered with moss later. Because the epoxy sticks to the rock, it can be a pain to remove when disassembling the hardscape.

The larger rock pieces in this tank were joined using epoxy putty.

Liquid super glue and cigarette filters/Nylon material

This interesting approach has been pioneered in Indonesia. When liquid superglue is added to cigarette filter material (cellulose acetate), the spongy material hardens instantly. The cigarette filter acts as a contact filler between two hard surfaces before the liquid superglue is added, so even uneven surfaces can be easily bonded using this method. Because the mixture cures instantly (faster than any other method here), it allows you to quickly build intricate hardscape structures, even at odd angles or uneven joints.

Liquid superglue will also react with other plastic materials such as nylon. However, it does not react with tissue paper or cotton in the same way.

This is my favorite method for connecting hardscape pieces because it allows you to easily connect hardscape pieces in odd positions due to the quick cure time. If a larger piece of cigarette filter is used, the joint can also take a decent amount of weight. This allows you to work quickly from piece to piece as each piece cures instantly.

The downside of this method is that the hardscape will be stained with the remnants of the cigarette filter/glue mixture upon disassembly. The combination also produces unpleasant fumes, so a well-ventilated area is recommended. The white cigarette filter glue is also obvious unless used at hidden angles. Some aquarists rub aquasoil/coffee powder on such joints to mask the white coloration.

The strength of the bond also depends on the type of liquid superglue used. Some produce a much stronger bond with the cigarette filters. Additionally, liquid superglue can be used on its own in a similar way to the gel superglue above; as long as there is some contact area between the 2 surfaces, it will work. Liquid superglue has the advantage of curing much faster than gel superglue.

Liquid superglue is applied to joints that sandwich a cigarette filter. A chemical reaction occurs immediately and the joint cures within seconds. Due to the white color of the filter, it is best used at less visible angles or covered with moss. Some aquascapers also rub aquasoil or coffee grains into the joint to disguise it.

The joint is load bearing within seconds. Because of this fast joining method, elaborate hardscapes can be built in a matter of hours, with pieces of hardscape joined in quick succession. If the joints are hidden, the cigarette filters are not visible; those that cannot be hidden are easily covered with moss later.

Aquascaping foam/insulation foam

This is a newer product on the market and is often used in terrarium and paludarium set-ups as a filler and to bond between rock pieces. It is available in gray/black and other rock colors.

It comes in canisters that emit a stream of expanding foam that sticks to surfaces and hardens after some time. Because it hardens into a foam, it is not as strong a bond as epoxy or superglue unless there is a lot of contact surface area. However, it is great for filling gaps between rocks - this is its main use in aquascaping.

You can (should) pat the foam down to reduce its buoyancy. It has the ability to float hardscape if used in large quantities and not patted down.

Aquascape Foam sprays as a foam that contains a lot of air. It is difficult to control an exact amount, so it is best reserved for larger joints rather than fine work. Once sprayed, it sets quickly in a few minutes. The foam camouflages well as it comes in rock colors.

In this tank, the left and right pillars has been connected using aquascaping foam.

Silicon adhesive

This is similar to the glue that forms the gaskets in a tank. The downside of silicone is that it takes a long time to cure, which means that if we are building a structure where the joints need to cure quickly and be able to support weight so that we can move on to the next step of construction immediately, this method is not going to be suitable. It cures in a few minutes, so it can be good for just keeping things from moving around too much. Silicone, however, takes 24 hours to cure to full strength.

This is best used for simpler hardscape designs where the rock/wood is held in place by gravity and the adhesive is only used to prevent the hardscape from moving too much. The entire hardscape can then be glued down all at once and left to dry. The joints will also not hold much weight unless the contact area is significant and clean. The advantage is that silicone is fairly easy to remove when the hardscape is taken down.

I would use this for scapes where the entire structure will hold its shape due to gravity, and all the pieces can be glued together at once and then left to dry.