Underwater Chemical Anchoring: How to Design and Install It

In ports, swimming pools and water-logged sites, anchors often have to be installed below the waterline — almost always with chemical anchoring. Many designers are wary of it, but there is really no reason to be.

Below is the correct process for designing and carrying out underwater anchoring, in a few clear steps.

Corrosion resistance below the waterline

The first thing to address is corrosion. There are several workable solutions:

• Chemical stud in SS316 stainless steel — the most standard solution. In seawater SS316 will not last forever, but it is a good medium- to long-term choice.
• Chemical stud in HCR stainless steel — HCR (High Corrosion Resistant) steel effectively never corrodes and is an excellent long-term solution, but it is so expensive that few contractors agree to pay for it.
• Fibreglass rod — an excellent long-term option, though it needs thought at the design stage and does not suit every situation. The rod itself is very strong in tension (roughly three times stronger than stainless steel), but the connection between the nut and the rod is weak (roughly three times weaker than a standard bolt and nut). In practice this makes it better suited to rebar dowels than to anchors with a nut.
• Epoxy-coated rebar dowels — bonded into the existing concrete and used as starter bars for a new pour, so that once the new concrete is cast the dowels are no longer in contact with the water.

Choosing the chemical adhesive

For bonding, the usual choice is an advanced epoxy adhesive with approval and proven underwater experience, such as Chemfix100, which is based on pure epoxy. Some vinylester adhesives also carry European approval for underwater use, but to the best of our knowledge there is no practical track record of using them below the waterline in Israel. We recommend the adhesives that are both theoretically better and, in practice, more established here — the advanced epoxy-based systems.

Carrying out the installation

The process is exactly the same as a normal installation above water, and can be done with a standard injection gun:

• Drilling — drill the hole to suit the diameter of the chemical anchor.
• Injection — inject the adhesive, making sure the nozzle is right at the bottom of the hole before you begin.
• Setting the anchor — insert the chemical stud by hand, with a twisting motion.
• Curing — wait for a full cure. Under water, this takes roughly two days.

What is different from working on land

• Cleaning: unlike a standard installation, there is no need to blow the hole out with compressed air.
• Strength: the adhesive will develop somewhat less strength under water than in an installation on land — allow for this in the design.
• Equipment: there is no special restriction on the diver; standard injection tools work perfectly well under water.