What pressure is the substrate subjected to?

A frequent concern, particularly for concrete injection, is the injection pressure. Clients want to know what pressure we pump at, as they are concerned what pressure the substrate will be subjected to. The simple answer is: if injection is done well, none.

Pressure is force over area, P = F/A. The pumps we use for concrete waterproofing have a pressure range from approximately 80 to 220 bar. The opening of a typical injection packer *) has a diameter of just under 2mm, giving an open area of about 2.5sqmm. 80bar over 2.5sqmm equals a force of 20N, or 2kg, which would be the force needed to hold shut the injection packer with your thumb.

When injecting, an experienced injector knows to ensure that there is a free flow of material at all times. This means the pressure the pump exerts is used solely to overcome gravity and friction to facilitate moving the resin from the tin through the hose, and maybe lance, to the packer. There is no pressure onto the substrate. The art of injection is to set up the drill holes to ensure any air or water can escape, and to be pay close attention to the flow of the material and any change in pump speed or sound, which might indicate a reduction in the flow rate. In which case injection is adjusted, or if necessary stopped, straight away.

*) Packers are the devices allowing to connect the pump with the structure. They usually contain non-return valves to prevent resin from escaping. There are various designs, some of which may require removal on completion of the work, others do not.

What’s the difference between polyurethane, acrylic and epoxy resin?

Simply, all are polymers. They start life in a liquid form and, once reacted, form a solid. The best way to find the most suitable resin for your requirements is to speak to the manufacturer - or to us. Here is a rough guide:

Polyurethane (PU) Resins

Polyurethanes (or PUs) are a polymer family best known for their foaming characteristics. The foaming ratio varies, depending on the intended use. PUs are tailored for different applications, with a variety of hardness, cure speeds, viscosities, and mechanical properties. They have excellent adhesion to various substrates and, depending on the PU, can be used to return physical properties to damaged surfaces or offer waterproofing capabilities. So selecting the correct PU is essential. 

The PUs we inject fall roughly into two categories:

(1)   Waterproofing PUs: these are mostly single shot, react only with water, and can cure into foams of different flexibility - from a flexible seal, to a tough, rigid foam. Reaction time can be controlled with the use of a catalyst.

(2)   Ground engineering PUs: these are mostly two-component resins that also only react with water and come in different viscosities, strengths and expansion capacities.

Acrylic Resins

acrylic (adj.) "of or containing acryl," the name of a radical derived from acrolein (1843), the name of the liquid in onions and garlic that give them the pungent smell, from Latin acer "sharp" + olere "to smell"+ -in.

‘Acrylic’ means derived from acrylic acid, and in general the term refers to the presence of acrylate and methacrylate esters in the polymer structure. 

Injectable acrylics are the least hazardous of the construction chemical polymers as they are generally based on water soluble chemistries. Acrylics swell when water is present, achieving the waterproof characteristics whilst maintaining good chemical and thermal resistance and a system that is fully biocompatible.

Injectable acrylic resins are really a system of components - acrylic, accelerator, and hardener - that remains in fluid form indefinitely until the catalyst is added to make it set. This allows an experienced injector to fully control the reaction time to suit the client’s requirements. Acrylic resins have less adhesion than PUs, so can be easily removed if needed, e.g. around services. They can have an added corrosion inhibitor, if required.

We use acrylic resins predominantly where their ultra-low viscosities are an advantage for penetration into hairline and fine cracks. Geotechnical grades of the injectable acrylics achieve even lower viscosities offering the same waterproofing properties with a less reactive system to allow for further penetration. Again, there are a wide variety of options, so speaking to the manufacturer or an experienced injector is advisable.

Epoxy Resins

Epoxy resins are organic chemicals that come in a variety of viscosities. As the acrylics, epoxies are a system, in this case compromising two reactive components: the epoxy resin and its hardener. When the two components are mixed, a chemical reaction takes place and the liquid resin gradually hardens to a solid plastic.

The wide range of hardener chemistries available mean that different epoxy systems can offer a wide range of physical and mechanical properties that should be considered when specifying an epoxy system. 

All epoxy systems offer a chemical and thermal resistance with excellent adhesion to common construction substrates. While epoxy systems have different reaction times and viscosities, they do not offer the on-site variation in reaction time of polyurethanes and acrylics.

Epoxy systems are used in various way:

1)    Injectable low viscosity resin, which are moisture insensitive

2)    Two-component (2K) pre-filled mortars

3)    Three-component (3K) mortars with variable filler content

We use epoxy resins as a structural adhesive: because the resins exhibit extremely high strength once cured, they can restore structural integrity, e.g. when injected into cracked concrete. 

What pumps do you use for injection?

We use two different types of pumps: electric and air-driven.

Electric Pumps

Our electric pumps are 110V single-piston airless sprayers, which we found best suited for small volume resin injection. Versatile, reliable, and compact enough to fit through manholes and be carried through confined spaces, our electric pumps have proven a key piece of injection equipment for all single-shot, and some two-component, systems.

Air-driven Pumps

The air-driven pumps are used for volume pumping: these can be either twin-piston pumps, or diaphragm pumps. The twin piston pumps come in different set ups, with different air heads achieving different pressures ranges, from ratios of approximately 1:6 to 1:40.

The diaphragm pumps are the lowest pressure pumps, used mostly for the latex-cement blend injection for masonry strengthening. This ‘flap swing check valve’ pump and is a 1:1 pressure ratio design, so air pressure equals pump pressure. This set up is particularly suited for heritage repairs.

We also have a couple of manual pumps, which can be useful for very delicate, small scale work, or where there is no power supply.