Sorry to hear about the cracks.
The only way to be sure exactly what these cracks are is to sand them down until they disappear.
There are many layers of different material in the bottom of your iSonic.
Yours is WOOD construction if I remember correctly.
The paint on the bottom goes on over a thin 0.026" mm wood veneer layer.
The wood veneer layer is saturated in epoxy resin so it's supposed to be fully sealed.
Below the saturated wood layer you will find a layer of thin fiberglass then a layer of hard foam.
If you sand the area of the crack down a bit I suspect you will find that the crack does not extend
below the wood layer and that there may be a little area of the wood that didn't get fully saturated with
resin at the factory.
If you look at "The Board Lady" website, she suggests a special "penetrating resin" for repairs like this
it's thin and made to be easily absorbed by cracks and by unsaturated wood.
If the crack goes deeper, you would need to sand/file/grind it down until it disappears and then rebuild the layers with the same or similar materials.
Might be better use a curved half round diemakers riffler to determine the crack depth as this will put a nice radius on both sides of the crack as it removes the material and will be stronger and easier to fair in when you rebuild it back with penetrating resin and then paint.
Hope this helps,
Last edited by Roger; 28th September 2012 at 10:38 PM.