3M Super 77 Spray Adhesive
There have been several posts on this issue, but none that address the issue as well as this explanation I found on another site.
3M recently made a formula change to their Super 77 Spray Adhesive, to meet the new California Air Quality Management District Rule 1168. This required the solvent cyclohexane in the old 3M Super 77 formula to be replaced with acetone. If used inappropriately, acetone-based adhesives can dissolve the EPS and Styrofoam components of your foam model. The 3M corporation suggests the use of 3M Insulation 78 Spray Adhesive as a replacement adhesive for the bonding of Styrofoam. The formula change does not affect application onto EPP foam.
To determine if you have the new or old formula, check the can. The old formula is packaged in the familiar, all black can. The new formula can is dark orange fading to brown and finally to black. Read the contents on the back of the can to be absolutely certain which formula you have. Following the word “Contains”, the old formula lists “cyclohexane” as the first ingredient. The new formula lists “acetone” as the first ingredient.
Follow these procedures when using the new Super 77 formula on foam. Practice on a piece of scrap foam to get the hang of it.
To apply Super 77 spray adhesive prior to taping or covering, hold the can 18 inches from the surface and apply a light coat. Allow15 minutes drying time between coats. Apply a second (and third, if needed) light coat.
To join foam pieces together (or to some other material), spray some adhesive into a disposable paper cup (remember what it does to foam?). Stir the glue for about 15 minutes to evaporate the acetone. With a small brush or a piece of scrap foam, apply thin coats of the glue to the surfaces to be joined. 5-minute epoxy is a more foam-friendly way to make these joints.
Remember to check behind the new formula cans to see if there are any old formula cans hidden away. California is getting to be a real pain in the rear. Now I read in Model Aviation that the FAA out there has determined that it has the authority to regulate model planes too. What's next?