If you brush it on as is and wipe it off tight with a credit card it works great. Brush some on(a fairly adequate amount) without going to far then wipe tight with a credit card and recycle the wiped stuff back into the jar and then thin the jar a little as needed with cheap Walmart pure fingernail polish remover acetone. Works great and easy to acquire I believe SIG is the best sanding sealer and thick is a good thing. Just my opinion and the way I like to do it. There are many ways to make balsa look like glass which includes not only the filling of the balsa but wet sanding primer and coats of paint.