I am almost through with building my very first kit. However, I am having a small problem with some balsa filler. Twice now, I have filled an area with balsa filler. Both times, after drying, I sanded the area and both times, little 'chucks of balsa filler fell out. Any suggestions on what I might do cure this problem?

How deep is the patch? also, I sometimes wet the area to be patched , so the filler will wick into the wood better, and bond a bit better. NOT WET WET BUT DAMP Are you sure the filler is completly dry? It's important for it to be dry before sanding.

oh yes, the balsa was totally dry. The depth was only about 1/8 to 1/4 in spots. I never tried the dampening thing. I'll give it a try. Thank you

I ment , the filler being totally dry, it's ok for the balsa to be damp while filling , just let it totally dry before sanding

Yes, the filler itself was totally dry. But I never thought of dampening the wood to make it bond better.
I'll give it a try. Thanks

1/4" is pretty deep. I would think that balsa fillers are more suitable for surface flaws. could you post a pic of what you are trying to fill ?

Hello, Buz has the answer by dampening the wood slightly. I might add...that if it was a deep dent, the "surface can be dry.... but underneath is still not cured. I know because I had the same thing happen to me once. I also have a suggestion when storing the balsa filler. I have a water bottle with a VERY fine mist that I use to sometimes spray on balsa for various reasons. BEFORE closing up my balsa filler I give the contents a "short blast" of water mist. I also spray a little on the inside of the lid. The idea here is to keep moisture in the container to keep the filler from drying out. Just don't OVER DO it, as you can weaken the mixture with too much water. I also have had problems smoothing a surface sometimes by messing around too long. Again.... a quick, short, blast of water mist will help the spatchula glide over the filler and keep it from "pulling up " imperfection etc. Again, be very careful not to get it wet!!
Good luck......lownslo

1/4" IS pretty deep, You may want to fill it with glue (if it's a crack) or a small chunk of balsa first. Also, what kind of filler are you using? "I use Elmers Wood Filler for Light Wood" and it works great.

I've switched over to the new "Pink" ultralight spackle. Cheaper and lighter than hobby shop balsa filler. Also, it goes on pink and stays pink until it is dry enough to sand, when it turns white. I'm using "DAP" brand "DryDex", but Red Devil and Elmers are selling similar products.

1/4 of an inch is a big gap to be filling with any kind of filler though. Filler has just about NO structural strength.

Dont understand 1/4" deep gap?, but, as Minnflyer said, fill it with epoxy or glue or thick ca if for nothing else, to get the strength back from whatever caused this "flaw"" in the structure.
Dont try to completely fill the gap with the glue though, if overdone, it will not sand down at the same rate as balsa or plywood and youll be left with a hump with thin balsa on each side.

sugarfoot, mix epoxy with micro-balloons and fill the largest gap. the micro-balloons reduces the weight and makes epoxy sandable.