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G/flex 650 Epoxy

The G/flex range is available in several sizes and in two different types, thickened (655) andunthickened (650). It is also available in repair kits. The additional product seen here, Six10, is another gap filling adhesive that self-mixes in the nozzle.

What is it? G/flex 650 Epoxy is described as a ‘toughened, resilient two-part epoxy engineered for a superior grip to metals, plastics, glass, masonry, fibreglass and wet and difficult-to-bond woods.’

Used for? Basically, all those difficult jobs, the bonds most likely to fail after using standard DIY adhesives. Typical examples would be where there are going to be stresses from expansion, contraction, shock or vibration. It is also good for bonding different density materials that are traditionally hard to glue together. These include attaching the PVC tubes of an inflatable to a GRP transom, or closed cell foam insulation to a curved bulkhead. If the job is a tricky one, G/flex 650 or the thickened 655 is most likely to be the answer.

Mixing ratio? A very simple 1:1 mix ratio by volume, or 1.2 parts of resin to 1 part hardener by weight. This will give a pot life of 45 minutes and a long ‘open’ time of 75 minutes at room temperature. The initial cure is reached in 3-4 hours, with a workable cure in 7-10 hours depending on the temperature. Getting the ratios spot on will ensure the most effective bond.

G/Flex has a simple 1:1 ratio by volume. Here it is being poured into calibrated measuring jars. Because the temperature is around 10°C, the epoxy is quite thick, so pours very slowly. Pre-warming the product indoors – or in an epoxy cabinet – will make the components more workable.

Hamish’s tips:

G/flex 650 is available in two distinct types, 650 Epoxy and the pre-thickened 655 Epoxy Adhesive. Both will produce a really strong bond, even to exotic materials. As the name suggests, the bond will tolerate a lot of flexing.”

Use 650 for fabrics and metals

“The G/flex range was developed by the Gougeon Brothers to tackle some of the most difficult bonding challenges. The standard 650 Epoxy is a liquid resin and hardener, to which you can mix some additives such as colloidal silica if necessary. In its unaltered state, G/flex 650 Epoxy is excellent at bonding fabrics such as kevlar,carbon fibre and aramids to substrates like GRP, polypropylene or glass. (If the driving mirror in your car has fallen off the windscreen, reach for the G/flex). It is often used to add reinforcing pads to the inside of white water canoes, as it flexes easily when the canoe hits a rock, or is twisted by powerful currents.”

Hamish also says that G/flex 650 was designed to tackle a very American problem, opening seams in metal boats.

“The US has vast numbers of aluminium boats, which are builtusing rivets. As the hulls wear the rivets work loose and water can get in. G/flex 650 is perfect for injecting into the rivet holes or along opening seams, to make a flexible watertight seal. The treatment also helps prevent any further degradation.”

Use 655 Epoxy Adhesive for mainstream bonding

“The 655 version is G/flex 650 thickened to make it more useful for bonding applications,” Hamish says. “Typical uses would be on foams, wood to glass, or any job where a thicker adhesive will produce better results. We know lots of people who have used it to successfully bond the soles of their work boots back on, as the cured epoxy can move with the rubber and leather.”

The flexibility of the cured product is what makes it so versatile.

“The cured product is really robust,” Hamish says. “You can hit it repeatedly with a hammer and it won’t shatter. Check out the YouTube video of a canoe being cut in half and then bonded back together using G/flex 655. It is back in action the very next day and as strong as it was before.”

A typical bonding job

A 25mm high density closed-cell foam needs to be bonded to a GRP minor partition.  The GRP has been prepared with cleaning and abrasive sanding and now the measured G/flex is poured onto a piece of scrap material for mixing.

Both measuring pots are carefully scraped out to ensure the ratio remains consistent.

Then the two components are thoroughly mixed together. Make sure both components are fully combined, with any runs and spills also pulled into the mix.

This is G/flex 650 Epoxy, it is a liquid but can be thickened with 406 Colloidal Silica additive for a thickened glue. However, this consistency is adequate for our needs, so the mix is then spread out over the inside of the partition. The adhesive stops short of the actual edge of the foam by 3-4mm to allow for squeeze.

The pre-cut foam is then pushed into shape. The epoxy allows the foam to be quite easily moved around on the substrate and the 75 minutes of ‘open’ (workable) time allows for plenty of repositioning and adjustment.

Happy that the foam is properly aligned, a heavy weight is placed on top (this foam is very stiff and hard to compress) to push the foam flat to the surface. Any 650 that is squeezed out is scooped up with a plastic chisel edged mixing stick.

As a little bit is left over, it is used to repair a set of old car keys where the metal shank has come adrift from its plastic keeper. If you are unsure of the quantities you need, then having a couple of other jobs ready means that nothing is wasted.

After curing overnight, the G/flex has successfully anchored this foam to the GRP. (Eagle-eyed readers will note that this is a larger partition and one we made earlier).

Unlike impact or ‘contact’ adhesives, this will not be affected by temperature. Some impact glues, especially those that get used for jobs in an engine-rooms, can loosen in excessive heat but the 650 will remain rock solid.

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