Because it expands.
I will be sheeting a NWHT Corsair fuse soon and it does not come in the foam shucks.
I can not think of any other way (besides vac bagging) to glue the sheets to the fuse and keep constant pressure on them to adhere the sheets. Contact glue seems the only way to do this.
I've tried and failed misserably to use NWHT own foam bond (Le'Pages white glue) on the wings so I wanted to try something else. I've had great success in the past using 3M Super 77 spray but they've changed the formula and I've heard it eats foam now.
Any one have any other ideas or know of a good contact glue?

Thanks.