Fiberglassing balsa fuselage

[KEZ]

Hi All,

My usual finishing process is to use thinned epoxy to attach 0.6oz cloth. After the epoxy cures, I would apply another coat of epoxy (full strength) to fill in the weave. Then I would sand, primer and paint.

I am wondering if a lighter finish can be achieved by spraying the primer instead of the second coat of epoxy to fill the weave.

I would appreciated your advice/experience.

Regards,
Kez

[dustn]

i've used drywall spackle before... very light and easy to use.

[m_acree]

You might also try mixing a lightweight filler material like micro-balloons with the epoxy until you get a peanut butter consistency. Apply to the unpainted surface. That will give you get a lightweight sandable finish.

[BMatthews]

For that light a cloth I would also suggest the primer instead of a second coat of epoxy. The weave of 0.6 oz cloth is so fine that a second coat of epoxy will be harder to sand off easily. However having used the lightweight wall filler compound I found it was hard to spread evenly in very thin coats even when thinned with water. For 2 or 4 oz cloth it works great but for the fine 0.6 oz cloth it just balls up and fails to fill the weave. I suppose the fine spreading wall compound would be fine but it's heavy and needs to be totally sanded off except for the bits in the weave. Spray auto primer is much easier to handle and wet sands off very well. Something you can't do with the fine premixed wall compound.

In any event it's very important to sand it all off except what's in the weave to ensure light weight. A final dusted on coat followed by light sanding will ensure a nicer base for the follow on paint but it'll weigh more. But truly nice finishes are often heavier than the super light options.

PS: for a lighter option than epoxy you may want to try clear model dope for the initial layup bonding agent. It'll dry away to a lighter binder than the epoxy and you can then fill the grain with the options above. I would dope the balsa with three thin coats with light sanding between to remove the fuzz and then apply the glass using thinner to flow through the glass and melt the dope underneath. Some light brushing will push the glass into the softened dope nicely. I've done two projects with this method and it works fine. It's not as strong but then this light a grade of glass is more for finish than strength anyway. Another option is to use tissue paper if the curves are not too compound in shape.

[dustn]

come to think of it i was using the spackle on heavier cloth.

[KEZ]

Thanks Guys for sharing your experience. I have decided to use a rattle can primer instead of a second filling coat of epoxy. It would be very messy sanding the primer off though as I can not wet sand it (there are exposed bare balsa and I don;t want to get those parts wet.)
Regards,
Kez