FAQs
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.
What other grouts do you inject?
Grouting refers to the injection of pumpable materials into soil or rock (here’s a good article on Grouting in Civil Engineering: https://www.designingbuildings.co.uk/wiki/Grouting_in_civil_engineering).
So grout is anything that can be pumped, and includes the resins described above. Apart from these polymer resins, and standard pre-bagged cementitious grouts, we also inject the following:
1. Latex-cement blend
2. Silicate Resins
3. Lime (see Lime Injection)
Latex-cement Blend
This is a product Tempo-PCE developed in conjunction with Normet UK, and successfully applied in a series of masonry structures. It is a polymer emulsion designed to be combined with a microfine cement to create a highly flowable injection grout, particularly suited for the rehabilitation of masonry arches. When injected, the grout replaces deteriorated or missing mortar and penetrates deep into the brick pores, creating a strong bond within the structure and improving compressive and flexural strength.
Silicate Resins
Silicate resins are environmentally friendly and highly stable colloidal silica. Their ultra-low viscosity makes them ideal where very slow migration and penetration are required. They come in different grades with varying SiO2 content, and the accelerator dosage can be adjusted to suit the ground conditions. The chemical properties and hydrophilic nature of silicate resins ensure excellent adhesion to wet surfaces or saturated substrates, and they are primarily used for injection into sands, silts, and fissures in rock strata.
How is injection pressure controlled?
Tempo-PCE generally uses a free-flow pumping technique. While the resin has an open route through the packer and into the crack, joint, void or surrounding ground, there is normally very little back-pressure at the injection head. The material is flowing freely rather than being forced into a closed space.
As containment develops—for example, as the treatment area fills, the resin reaches a restricted section or the material begins to react—resistance increases. This change is immediately apparent to the operative through
a change in the sound of the pump as it comes under load
a reduction in the pump’s cycling or delivery rate
an increase in the pressure-gauge reading
reduced material flow
resin appearing at adjacent packers or designated outlets
An experieneced operator can therefore respond immediately by reducing the delivery rate, stopping injection or transferring to the next packer.
The pressure displayed at the pump is principally the pressure required to overcome resistance in the hose, valves, packer and injection pathway. It should not be interpreted as a uniform pressure acting across the structure. Nevertheless, some positive pressure is required to create flow and overcome groundwater pressure, so it would be incorrect to say that the substrate experiences absolutely no pressure.
The objective is to maintain free, controlled resin movement using the lowest effective pressure. Injection is not continued against a closed or fully contained system. Pressure, flow, resin volume, pump behaviour and movement through the treatment area are monitored together throughout the operation.
For reactive polyurethane resins, any expansion pressure generated after injection is considered separately from the pumping pressure.
