A Comprehensive Guide to Polymer Modified Mortars and Epoxy Systems in Construction
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 work. 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 according to the manufacturer’s instructions. The mixture is stirred until creamy. The grout 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 after 28 days at least 5 Kgf/cm2)
- Compressive strength after 28 days from 250 to 450 Kgf/cm2
- Flexural tensile strength 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 require only water addition at the job site.
Advantages: Controlled manufacturing, precise dosing, designed for specific purposes, particularly suitable for repair work where product quality is essential and/or on-site mixing capabilities are limited.
Types:
- Mortar repair: Low shrinkage, controlled shrinkage, and/or ripple effect.
- Fast Set Mortar: High-speed setting for quick jobs.
- Thixotropic mortars: Suitable consistency for vertical and overhead applications without sagging.
- Mortar screed: Flowable, for application on horizontal surfaces (floors).
- Grout Mortars or filled: Generally expansive fluids for injections and fillers, suitable for work in tight spaces.
PROPERTIES
Specific properties vary from one product to another and between different manufacturers. They are generally characterized by high strength (over 300Kgf/cm2), rapid strength development, 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 needed. 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) as indicated by the manufacturer. In most cases, complete pre-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:
- Liquids with varying viscosity depending on the formulation.
- Thick consistency pastes by adding quartz powder and possibly a thixotropic agent.
- Epoxy Mortar: Adding sand, usually quartz, of a specific size distribution to the resin-hardener 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 20°C, depending on the formulation. The viscosity can be increased with fillers to form thixotropic pastes. Conversely, low viscosity products are available for injection work.
REACTION 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.
SHRINKAGE
Hardening occurs with virtually no shrinkage.
MECHANICAL PROPERTIES
- Compressive strength: 400 to 1000 Kgf/cm2 at 7 days
- Flexural tensile strength: 200 to 800 Kgf/cm2 at 7 days
- Adhesion to steel: over 200 Kgf/cm2
- Adhesion to concrete: 50 Kgf/cm2 concrete rupture
- Modulus of Elasticity: 10,000 to 350,000 Kgf/cm2 depending on formulation and filler content
- Thermal sensitivity: The application temperature influences the viscosity and velocity.