Good day,

I am intending to use fibreglass as the covering material for the aircraft I am currently constructing. However, what to use with the fibreglass is becoming a problem. I know I require the actual 'fine-thread' fibreglass sheet, but the resin and hardener side is giving rise to confusion. I have come across two particular types of resin; standard resin and 'epoxy' resin.

In brief, the question is, do I still need hardener if I use an 'epoxy' resin? Epoxy is an adhesive, thus this raises the question as to whether hardener is required or not. Can the resin just be brushed onto the fibreglass sheet without mixing it with the troublesome hardener?

Epoxy is always a two-part system.

You'll find it much more trouble without the hardener.

It hardens to a stiffer, harder final surface than the 'standard' resin, which is most likely polyester.

Buy a small amount and do a test lamination on some scrap balsa. I think you'll like the results.

Thank you for the advice.

Quite correct, the other resin is polyester.

One final question: is the resin to be brushed onto the fibreglass before being mixed with the hardener and left to dry to a certain extent? It is quite difficult to get a successful mix of the two ,which are vastly different in their densities, prior to application. Taking into account that the resin liquid comes in a tin and the hardener has to be squeezed out of a tube makes things that bit more difficult!

All mixing and stirring of components should be done before any surface application.

Catalysation of polyester can be rather difficult, considering the small percentage (1-2%) of hardener required to start the cure.

However, epoxy, depending upon which brand you buy, is usually combined at a much higher percentage, so it's easier to get the mix done more accurately.

Pick up a small postage scale, something that will show you a gram or ounce readout, and then you'll be able to combine them at exactly the percentage required. I use the West system epoxy, which mixes at a relatively easy to measure, 5:1 ratio.

The ratio you have quoted certainly seems familiar; for every 5 units of resin, add 1 unit of hardener.

I think I may have made life slightly easier by paneling the aircraft frame with balsa wood, which provides a nice solid backing for the fibreglass to stretch over. I have a few bad memories of my attempt at a slightly old-fashioned method of covering (on a different aircraft); tissue and dope over an uncovered frame - it just did not prevail. The dope was pasted on with a brush, thus I am assuming I can use a standard brush to apply the resin and hardener mixture.

Many thanks.

Right, about the brush application.

Apply the resin coat to the balsa surface, then add the material, letting the resin soak up though the weave.

A final brushing over any dry spots, perhaps using a small plastic squeegee, such as used for applying auto body filler, can be used to smooth the weave out and eliminate any bubbles.

Move the squeegee from the center out toward the edges, for best results. If your plastic squeegee gets nicked along the working edge, just 'polish' it by rubbing back and forth on a section of cardboard.

That is a sound idea. I have a plastic 'squeegee' which accompanies some car filler in my garage. As you have made clear, it will make life easier.

I am interested in the application method you have suggested. I am now confident I will be able to undertake this method successfully, but I would just like to clarify a few points. I am under the assumption that the resin coat which is applied to the balsa is just resin and not mixed with hardener. I am also assuming that the final coat of resin/hardener mix is applied once the fibreglass and initial resin have totally dried and set.

Thank you.

just to maybe help you out never ever put resin on anything without first mixing in the hardner.also the same for epoxys.they will never never harden if you do not add the catalist

Thank you - I will make sure that first coat of resin on the balsa wood is mixed with hardener.