10 myths about epoxy resins – Stiffness / strength / strength 2 part

10 myths about epoxy resins – Stiffness / strength / strength 2 part

Our epoxy expert David Johnson confirmed that epoxy definitely sticks to polyester – and also has better adhesion values. In this series of breaking myths, we will break the myth of strength / strength and discover how good it is for repairs.

Myth: 3 epoxy is not as good as polyester for repairs

It’s a very strange myth and we’re not sure where it comes from. Yes, polyester resin is incredibly strong but when it comes to repairs, epoxy is much better than any other resin system.

First thing, epoxy repairs do not retract. Polyester is retracted because it contains styrene and these styrene molecules evaporate when the resin hardens. On a small surface this might be fine but repairing larger areas will create “stress” on that surface even before we return the boat to the water.

Another thing, of course, is inhaling all that styrene when mixed and working with polyester resin which is by no means good – especially if you work indoors. You may feel dizzy, drowsy, etc. This is just the beginning. Epoxy, on the other hand, does not contain these volatile organic compounds and is cleaner and easier to mix, especially if you use the simple set pump that comes with WEST SYSTEM products.

There is also a lot of evidence that epoxy is much more water-resistant than polyester resin, which is important when repairing ships below the waterline.

It is generally accepted that the polyester bond is about 20% weaker than the bond made by epoxy. Of course, if you want to look at water-resistance science, many years ago our American partners did an experiment on the “moisture-wicking efficiency” of epoxy (and various types of other coatings) on wood.

It was in the lab and under specific conditions but WEST SYSTEM 105 Epoxy Resin with 205 Quick Hardener finished in first place, demonstrating more than 80% water resistance after 6 weeks of continuous exposure to moisture. After the same time period, the polyester resin was just over 30% water-resistant. It has also been found that the rate of loss of water resistance of polyester increases with time.

Myth 4: Epoxy is more brittle than polyester

We heard a couple of people ask if epoxy is a mole, especially when used with wood. Of course, the chemistry of epoxy is such that it lengthens in order to bend – even in a wooden structure.

The typical elasticity of polyester is between 2-3%, while with WEST SYSTEM epoxy it is over 4%. This means that if we use epoxy we will create a material that is much more resistant to constant loads than polyester.

Take for example a light boat, it will be loaded with various dynamic loads from the water, deck equipment, sails and so on and if it is made of polyester – which is not elastic enough – micro cracks will form. This will result in the laminate becoming softer and softer.

However, if you use epoxy it will be much more resistant as it will stretch more. After curing, epoxy will give better results in terms of strength and improved elasticity, and thus improve the quality of the final product.

So, the simple answer to this myth is: NO, definitely not!

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