Wessex System 328: Mixing, application and storage
Any unsound material must be cut back to uncover sound concrete. The surface must then be degreased.
Floor Tiles Covering
The under surface must be dry, free of contamination and lightly abraded. Some products, e.g. Vamac, are supplied to these requirements but the under surface must be checked before the Wessex 328 epoxy is applied. If cloth-backed floorings are used, then any release agent must be removed before bonding. If in any doubt, degrease and then abrade before applying the adhesive.
It must be appreciated that any epoxide resin and hardener must be well mixed to produce homogeneity - an essential requirement to achieve ultimate bond strengths and with heavily filled systems such as the Wessex 328 epoxy, complete mixing is even more important. With the Wessex 328 pack, it is only necessary to pour the total contents of the polybucket containing the epoxide resin into the epoxide hardener and mix thoroughly for four minutes.
The larger the pack size, the more difficult and time-consuming the mixing operation becomes. The volume of the pack is blended into a homogeneous mass by mixing for a minimum of four minutes with an air driven mixer ideally having a large gate paddle. The differently coloured components provide a visual aid to complete mixing which is indicated when the adhesive forms a uniform colour and all signs of streakiness have disappeared.
As stated earlier, when the resin and hardener are homogeneously mixed, heat is generated as a result of the reaction which is taking place, i.e. an exothermic reaction. The heat which is generated speeds up the gelation time of the epoxy which, in turn, shortens the working time available. These properties are highlighted the tables below.
|Mass||Working Time at 25ºC||Gelation Time at 25ºC|
|1.4 40 55||40||55|
The above table indicates the mass effect on the working and gelation time of the Wessex 328 Flooring Adhesive at 25ºC.
The effect of temperature and mass on the working and gelation time of Wessex328 flooring adhesive
|TEMPERATURE||WORKING TIME||GELATION TIME|
|°C||1.4kg mass||6.0kg mass||Thin film 0.5mm thick||1.4kg mass||6.0kg mass|
High temperatures provide lower viscosities but between these temperatures this epoxy system will provide excellent wetting of the substrates with which it is in contact and good spreading/coverage characteristics.
When the epoxy composition has been thoroughly mixed for the stated period of time it is ready for use and within ten minutes must be applied to the substrates. Rough surfaces, such as a concrete floor, must be completely wetted and a thin coating spread onto the floor covering and the concrete floor to which it is to be bonded. In practice, it has been found when working with smooth, new surfaces, i.e. wood and metal, only the base floors need to be coated. A screeding tool such as a saw tooth scraper has been found to be the most suitable for applying the adhesive to a thickness of approximately 0.3mm - this will give a coverage of about 0.3kg/m² - and to obtain this thickness of coating, the scraper has a serrated edge having a minimum depth of 0.5mm. Immediately after application onto the substrates, the mixed epoxy will flow to the required uniform thickness and the floor covering can be positioned onto the floor. To ensure that intimate contact is maintained between the floor covering and the floor throughout the curing cycle, some weight should be placed onto the covering.
Physical Data Wessex 328 Adhesive
|Appearance||Specific Gravity||Flash Point(°C)|
|Resin Part A||Highly filled yellow liquid||1.5||>150|
|Hardener Part B||Highly filled blue liquid||1.4||>150|
|Mixed System (1:1 by weight)||Homogeneous green liquid no streakiness||1.45||>150|
Coverage: Between 0.3 & 0.5 kg/m²
Time to peak exotherm of 500g mass: 60 to 80 minutes (approx. gelation time)
The bond strength of the above epoxy mix when used as an adhesive between circular mild steel adherends (Test Method BS EN 26922) is greater than 4.38 MPa - the minimum requirements to meet specification - and the mode of failure is approximately 50% cohesive within the adhesive layer and 50% interfacial between the adhesive and the steel adherends. (This is one of the routine standard tests carried out on each batch of Wessex 328 epoxy by the Quality Assurance Laboratory). Typical strength values when tested to failure are approximately 16 MPa.
It is generally recognised that when bonding to aluminium, good adhesion is not achieved unless degreasing, abrading, priming and/or etching the substrate is undertaken.
In consequence, tests have been conducted with an Elcometer to determine the bond strength of Wessex 328 epoxy to extruded aluminium sections when the substrate has (i) only been degreased