Why do we clean up our builds?
Not only does it make your base build look cleaner, it also has a more practical reason. It helps save time. Even though contact adhesive dry flat when applied in thin layers, it gives the foam a different density and texture on the surface.
The second image shows exactly this. You can clearly see the part where the glue was left on as it soaks up the primer differently. This is after 3 layers of Hexflex primer. This is rectifiable but it will require more effort. I ended up having to do 6 layers of Hexflex and 3 layers of Seal Prime spray to get it looking more consistent.
Cleaning up your build before priming will also get rid of any excess lumps of glue that squirted out when layering foam together as well as cleaning up imperfect seams so it is easier to rectify with filler.
How do I remove glue stains?
Any glue remover or paint thinner will do the trick. I started off using Evo Stik Adhesive Cleaner but the smell got to my head really quickly. I would however recommend something that is labeled "low odour". The one I use now is from Poly-Props. If you're really cheap, you can just use white spirit. Just like intercourse, don't forget to use protection as these products will irritate your skin and worse, your lungs if you're not careful. Wrap a condom over your head for maximum protection.
You could also use the Evo Stik Adhesive Cleaner to soften up old glue so it's easier to work with. Just a word of warning, do not pour too much in! Only do little squirts at a time and ensure it is mixed in well before squirting some more in.