Wessex System 325: Adhesive strength and properties

Adhesive strength of Wessex 325

(a) On steel

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 325 epoxy by the Quality Assurance Laboratory). Typical strength values when tested to failure are approximately 16 MPa.

(b) On aluminium

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 325 epoxy to extruded aluminium sections when the substrate has (i) only been degreased and, (ii) a proprietary brand of primer has been subsequently applied. After seven days' conditioning at room temperature the average bond strength of the epoxy onto the degreased aluminium surface (it was not abraded) was 7 MPa from the six specimens tested and the coefficient of variation was low. In every instance, the mode of failure was 100% cohesive within the adhesive.

The coverage rate of the Wessex 325 epoxy for these tests on aluminium was about 0.5kg/m² spread, i.e. the adhesive thickness was approximately 0.33mm.


Part A, Resin:

Appearance: highly filled black coloured liquid

Viscosity (Brookfield RVF Spindle 7; Speed 10 rpm) : 450 Pas at 25°C

Specific Gravity: 1.5

Flash Point: >150°C

Part B, Hardener:

Appearance: highly filled buff coloured liquid

Viscosity (Brookfield RVF Spindle 7; Speed 10 rpm): 170 Pas at 25°C

Specific Gravity: 1.4

Flash Point: >150°C

Mix Properties

Wessex 325 Epoxide Resin, Part A: 100 parts by weight

Wessex 325 Epoxide Hardener, Part B: 100 parts by weight

Appearance: homogenous black liquid with no streakiness

Viscosity (Brookfield RVF Spindle 7; Speed 10 rpm): 196 Pas at 25°C

Specific Gravity: 1.45

Flash Point: >150°C

Coverage: between 0.3 - 0.4 kg/m²

Time to peak exotherm of 500g mass: 60 to 80 minutes (approx. gelation time)

Wessex 325 Epoxy Flooring Adhesive Fire Performance

BS 476 Part 7
(Spread of Flame)
Class 1 Class 1
BS 476 Part 6
(Fire Propagation)
Fire Propagation < 12 <12
Building Reg. 1991
(Appendix A, Clause 12
of the Approved Document B)
Class O Class O
BS 6853 Part B5.4 1977
(Smoke Emission)
< 150 Ao (abs) m2/m < 70 Ao (abs) m2/m
Toxic Fume Emission Metallic elements Magnesium, aluminium
LUL SD 6220-05-601 detected silicon, calcium
LUL SD 6220-05-001 Non-metallic elements detected Carbon < 40%
Nitrogen < 2.5%
Sulphur < 0.5%
Immediately Dangerous to Life
or Health HCN concentration
(LUL Code of Practice)
< 50 ppm < 30 ppm
BS 6401 1983
(Ds at 5 mins)
NBS Smoke Box
< 50 < 10

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