I do the backing to the batt and then spray the batt and smooth the top. I am on my nd case of 505 in the red can from France. Same product but far less expensive here in USA. I know you are in my homeland, so likely it isn't an option for you. I use a ping pong table for sandwiching now and I am going to try the Elmer Washable glue method soon! (When I run out of 505). I find that cotton batts work better than poly with the 505, but am so glad that someone here on the forum told us about it!