Balsa Filler
 

Hey Guys - What type of fillers are you using to fill gouges, cracks, gaps, etc. Easy to sand, and flexible. I have even heard about the use of drywall filler. Please advise. Thanks. Chic

Yeah,, no such thing,, anything that stays flexible can't really be easily sanded

I use regular lightweight Spackle on bare wood,, 410 filler/epoxy on glassed wood,,, so it depends on the covering what you'll want to use,,

I totally agree that anything flexible is not easily sanded if it can be sanded at all. Spackle is something that I find very useful for small imperfections in balsa becase it's easy to use and sands at about the same rate as balsa. Where I find fault with it however is that it doesn't have much strength to resist crumbling under any kind of stress.

My own favorite almost universal filler for all surfaces is a product called SpotLite by Evercoat. It's a final surfacing putty used primarily in the auto body industry and sands about as easily as spackle without clogging the sandpaper. It sets completely in 10 minutes at room temperature, is usable on all kinds of surfaces and is considerably more durable than spackle. It's also waterproof unlike spackle and can be wet sanded to a glass smooth finish. If there's any downside to it, it's that you have to work quickly with it or work a small section at a time. It's usually available from auto body suppliers or on line. And oh yes, the material sets up by adding hardener to it which must be mixed very thoroughly before using. Hardener is included with the material.

Does "Spotlife" have a shelf life? How does it compare to Bondo "Glazing & Spot Putty"?

TIA,
Jerry

Hi Jerry,

SpotLite is a material that is generically known as a 'polyester filling compound'. Among a wide range of such fillers that fit various purposes is Bondo.

At the beginning of the range of fillers are those designed for structural strength and some even contain fiberglass strands mixed in with the goop. Others focus on water resistance or lightness or flexibility or ease of sanding and so on as the line of fillers progresses toward finer applications.

SpotLite is on the fine end of the filler line and now one of the brands that takes the place of the more traditional lacquer- based red glazing (spot) putty that you might have seen smeared over body repairs on cars in the past. The advantage of polyester putty over the older lacquer putty is that you don't need to wait forever for the solvents to evaporate for it to be dry enough to sand and at the same time it doesn't shrink.

As I might have mentioned, SpotLite is not the only brand of this type of material, but it DEFINITELY IS a pleasure to sand this stuff as compared to at least a handful of other brands that I've tried!

If you've worked with Bondo then you already know how to handle SpotLite except maybe that it sets up a bit faster. Just think of it as a lighter, smoother, creamier version of Bondo that's a LOT nicer to sand!

Shelf life? With a tightly sealed lid and stored in a cool place, the stuff lasted me for years.

Any other questions... feel free to ask! ;)

Steve

huh,, never tried that product,, might have to try it,, I assume you only use that post glassing like spot putty,,not on bare balsa?

One of the great attributes of this stuff is that it can be used on bare balsa (I've often used it that way) as well as over glassed surfaces. It feathers beautifully with balsa and many other materials including metal, fiberglass, painted or primed surfaces, hard plastics such as styrene, acrylic, ABS, polycarbonate, urethane, etc. WILL NOT WORK WITH SOFT PLASTICS LIKE POLYETHYLENE, NYLON, DELRIN, ETC! That means it won't work well as fillet material for something like a plastic control horn. On the other hand, it CAN be used to blend a canopy into the fuselage.

If applied over primed or painted surfaces, make sure that the primer is completely dry and that the paint is completely cured.

It can also be used over foam that is not affected by solvents, but will not stick to PE. DO NOT USE ON STYROFOAM as it will attack and dissolve the foam.

It works very nicely as a seamless transition between dissimilar materials as long as the joints are at least slightly below the surface.

This stuff makes sanding to level, smooth or shape a surface almost fun to do!