Adhesive Terminology Pot life is a defined time during which the viscosity of the mixed system doubles. For example, if a mixed resin system has an initial viscosity of 10,000 cps and the viscosity increases to 20,000 cps after 30 minutes, then the pot life of that mixed adhesive/resin is 30 minutes. Open time is the time after application of an adhesive within which it will still form a successful bond. This can be influenced by the substrate; with absorbent substrates reducing open time; and also the ambient conditions where warm, dry conditions will reduce the open time. Full cure: An adhesive or sealant is said to have reached full cure when the chemical reaction is complete, and the ultimate bond strength has been reached. It is not uncommon for two-part systems to reach handle able strength within 15 to 20 minutes, yet still require 24 hours or more for the full cure cycle to complete. Elongation at break is the percentage increase in length that a fully cured material sample will achieve before breaking. This figure, shown as a percentage, is usually measured using test method ASTM D412. A higher number commonly indicates a better quality material when combined with a good tensile strength. Tensile strength is the resistance of a material to breaking under tension. In adhesives it is generally defined as the maximum stress that a material can withstand while being stretched or pulled before breaking. In testing a bonded sample is typically pulled to its breaking point to determine the ultimate tensile strength of the material. The amount of force applied to the sample and the elongation of the sample are measured throughout the test.
General Advice Care should always be taken when working with chemicals and suitable gloves and eye/face protection should be worn as required. Observe good industrial hygiene. In case of skin contamination wash immediately with plenty of soap and water and remove any contaminated clothing. To remove superglue from skin soak the affected area in warm, soapy water until the adhesive can be gently peeled from the skin. We do not recommend using solvent such as Acetone (nail varnish remover) to remove superglue from skin.
Substrates For optimum bond performance substrates should be clean, dry and free from any contaminants liable to impair adhesion; including dirt, dust, grease, oil, release agents, etc. Substrates should be allowed time to acclimatise to room temperature prior to bonding. Rigid plastics should be cleaned with an isopropyl based cleaner before bonding with tapes. Flexible plastics such as PVC and vinyl contain a lot of plasticiser. Plasticisers are commonly added to polyvinyl chloride (PVC), which otherwise is hard and brittle, to make it soft and pliable. A plasticiser resistant adhesive should be used to prevent plasticiser migration into the glue line. Adhesives that are unable to resist this migration will leech plasticiser from the substrate and become soft over time, resulting in a bond failure.
Contact Adhesives Contact adhesives work by forming a tacky surface after the evaporation of a solvent. Sufficient time should be allowed for solvent flash-off before consolidating the substrates and forming a bond. If substrates are assembled too quickly it can result in solvent entrapment; where residual solvent is not allowed to escape the glue line and full cure cannot be achieved. In most cases contact adhesives are applied to both substrates. This should be considered when calculating your bonded area.
Canister Adhesives Canisters taken from storage should be allowed time to acclimatise to room temperature before use. Canister systems keep the adhesive under pressure inside the hose, when not in use the trigger should be disabled by turning the locking nut. The valve on the canister should should be left open until the canister is empty. Turning the canister's valve off will reduce the pressure inside the hose causing any adhesive in the hose to begin curing, causing blockages. The locking nut on the spray gun can also be used to provide a narrower spray by restricting how far the trigger can be pulled. For optimum bond strength with web-spray systems; spray one surface horizontally and the other vertically to maximise contact between the glue lines.
PVA Adhesives Water based adhesives should be protected from frost. Product that has frozen and thawed should not be used in production.
Caravan & Mobile Home Repairs Floor Delamination Repairs: When repairing a delaminated floor always ensure that all preparation work is carried out prior to mixing the resin. This ensures the mixed epoxy remains at a workable viscosity for pumping into the floor void. Epoxy resins produce an exothermic reaction while curing, a larger mass of mixed resin will create more heat than a small deposit so care should be taken when leaving resin to cure in a bucket. Window Delamination Repairs: Acrylic windows used in caravans and motorhomes are susceptible to crazing if pressure is exerted on the glue line during the curing process. This is where micro-fractures can form in the curved edges of the plastic. When rebonding caravan windows the best results are achieved by floating the outer part on the glue line, the two parts should not be clamped or secured in a way that will put pressure on the glue line. For DIY repairs to caravan and motorhome windows we recommend Tremco SPO30.
