A Comprehensive Guide to Polymer Modified Mortars and Epoxy Systems
MORTARS WITH POLYMERS
Cement mortars with an emulsion of an acrylic polymer or synthetic latex added to them are known as polymer-modified mortars. The polymers currently used in the manufacture of these emulsions are of three types:
- Acrylics
- Styrene-butadiene rubber (SBR)
- Polyvinyl acetate (PVA)
These polymers are suitable for permanent wet environments. Polymer emulsions have two forms of application:
GROUT ADHESIVE
Used as a bonding bridge in fresh mortar and concrete or mortar bases for masonry. To prepare the grout, cement, bonding agent, and fine sand are mixed in a 1:1 ratio. Then, an acrylic emulsion diluted with water is added in the proportion provided by the manufacturer, mixing until creamy. The slurry is applied by brush on the surface, and the mortar must be applied fresh within an hour.
MORTARS WITH POLYMERS
Adding an acrylic emulsion to cement mortars significantly improves some of its properties:
- High adhesion to the base (resistance to cutting 28 more at least 5 Kgf/cm2
- Compressive strength after 28 days from 250 to 450 Kgf/cm2
- Flexural traction resistance after 28 days from 65 to 100 Kgf/cm2
- Compression modulus: 250,000 Kgf/cm2
- Low wing cracking tendency
The recommended dosage is from 1:3 to 1:3.5 (by weight) with a water-cement ratio between 0.30 and 0.40 (including acrylic emulsion previously dissolved in water). Mortars with polymers are primarily used in repair work and thin-layer applications.
DOSED MORTARS
Several products on the market are prepared in factories or plants and delivered ready for use or just require adding water at the job site.
Advantages:
- Controlled manufacturing
- Precise dosing
- Designed for specific purposes
- Suitable for repair work where product quality is essential and/or lacking control means
Types:
- Repair Mortar: Low shrinkage with controlled shrinkage and/or ripple effect.
- Fast Set Mortar: High-speed tightening for quick jobs.
- Thixotropic Mortars: Right consistency to work in vertical and overhead applications without sagging.
- Screed Mortar: Fluids, to apply to elements or horizontal surfaces (floors).
- Grout Mortars or Filled: Generally expansive fluids for injections and fillers, ideal for work in tight places.
PROPERTIES:
Specific properties vary from one product to another and between different manufacturers. They are generally characterized by high resistance (over 300Kgf/cm2), rapid development of resistance, good adhesion to concrete and masonry, and low shrinkage.
EPOXY SYSTEMS
These are synthetic products that harden by a chemical reaction between a resin and a hardener.
Common formulations include different types of hardeners, modifiers, solvents, and mineral fillers as appropriate. They are delivered in 2 or 3 components:
- Part “A” resin
- Part “B” Hardener
- Part “C” or aggregate filler
Dosages:
Carefully prepare the resin-hardener proportion (A:B) indicated by the manufacturer. In most cases, complete dosed sets are used.
The proportion of part “C” filler can be adjusted according to the work and consistency required properties.
Epoxy systems, depending on each use, may be used as:
- More or less viscous liquids depending on the formulation.
- Thick consistency pastes for which quartz powder is added and eventually a thixotropic agent.
- Epoxy Mortar: adding sand, usually quartz, of a certain size distribution to the resin-hardening blend. The ratio of hardener and resin plus sand is between 1:1 and 1:10 by weight. A+B/C = 1:1 to 1:10
VISCOSITY:
The viscosity of pure epoxy systems (without filler) can range between 100 and 2500 centipoise (cps) at 20ºC, depending on the formulation. The viscosity can be increased with fillers to form thixotropic pastes; conversely, low viscosity products are needed for injection work.
RETRACTION SPEED:
This determines the pot-life or initial setting time and the development of resistance to tight deadlines. It depends on the formulation, temperature, and volumes of mixtures. In general, high resistance is achieved at an early age, with the possibility of commissioning services within the first three days. The reactions are exothermic, which may limit the volumes to prepare.
RETRACTION:
Hardening with virtually no shrinkage.
MECHANICAL PROPERTIES:
- Compressive strength: 400 to 1000 Kgf/cm2 at 7 days
- Flexural traction resistance: 200 to 800 Kgf/cm2 at 7 days
- Adhesion to steel: over 200 Kgf/cm2
- Adhesion to concrete: 50 Kgf/cm2 rupture of concrete
- Modulus of Elasticity: 10,000 to 350,000 Kgf/cm2 according to formulation and filler content
- Thermal sensitivity: the application temperature influences the viscosity and velocity.