I got the bright idea of making a wing stronger by building it up, adding the pushrod tubes, sheeting it on the top and the bottom, and then filling the cells between the ribs with "NON" expanding foam between the leading edge and the main spar. I mistakenly thought that the excess would just go through the spars to the back ,but instead, it just puffed up the sheeting until my wing looked more like a mattress. I had to rip all the sheeting off and slice all the excess foam down to the ribs and then start over with the sheeting. I still use this method sometimes but now I apply the foam after only one side is sheeted and then wait a couple of days for everything to quit rising before slicing the foam down and sheeting the other side.