Fairing gloop

Has anyone found a lightweight fairing filler that isn't so tough that when you sand it, it is not tougher than the glass or foam around it. Tried various products but always they end up so dense that you do more damage to the surrounding areas than the hollow area you are trying to fill.

The best I have found so far is glass spheres and epoxy but it takes forever to cure hard enough to sand that it negates its purpose. Lightweight polyester car body filler mixed with about 25% glass spheres does a real cool job but just the thought of laying carbon etc up in epoxy then fairing it with polyester just doesn't seem right.

Any ideas anyone ?

My favorite gloop is a fairing mixture sold by US Composites, www.shopmaninc.com, and is a mixture of phenolic microspheres and colodial silica. The phenolic spheres are the reddish brown ones that feather much better than glass spheres. They sand quickly. Since you can use any type of unfilled epoxy resins with it, you can control cure time to suit your situation. If you want quick turn around, use one of the TETA based hardners with a 10 minute pot life.
I do not usually use any polyester based fillers on the outside of the boat or underwater. Epoxy has better adhesive properties and no water absorption. But I do admit to using Bondo on those last little tiny places I always seem to find after spraying primer. By that point I just want to get the whole thing over with!

That is how the pro fairers do it. 99.9% with epoxy and microballoons, then high build primer, then touch up small knicks with "car bog" before undercoat and gloss.

Alternatively, for smaller jobs, I've used a pre-mixed 1:1 filler called technifill instead of microballoons. It is a bit pricier but much easier to mix than balloons.

WEST 410 Microlight - Can't beat it.

Wayne,

why does your epoxy take ages to harden properly? 24 hours is sufficient even in my garage during winter (I do wear a mask, gloves and a tyvek or similar boilersuit with hood when sanding!).

The workshop where I play with my toys is usually unheated and at this time of year can be down around 10C, I usually blast it with a LPG heater to bring it up to about 20C whilst laying up glass etc though as the wet out is sooooo much easier.

It is not so much the drying time but the sanding time if that makes sense, even after 24hours using a fast set epoxy, when sanding you will find the discs clogging with epoxy, I presume the heat generated from the sanding disc is enough to soften the green epoxy.

Aha, yes sanding partially hardened epoxy is a real pain. It can not be done properly in my experience. Please remember to take all possible precautions when working with green epoxy. That stuff is just as bad as freshly mixed epoxy. Suit up, use gloves and wear a really good mask.

If glassing over wood, heating the wood will produce gas bubbles. Temperature should be falling if glassing over wood.