by wefalck » Sat Jul 17, 2021 10:07 am
The cements normally used when working with styrene consists mainly of a solvent and will weld to parts together, rather than act as medium of glue in between them. If parts are painted, the cement cannot work as desired.
A bond is only as strong as the weakest interfaces that are involved. So when you e.g. glue together one or two painted surfaces, the bond will only be as strong as the paint adheres to the surfaces.
Certain paints, such as organic solvent-based enamels (e.g. Humbrol) will fuse with styrene and form a firm bond, but plastic cements do not really dissolve the paints sufficiently to achieve the 'welding' effect, as observed, when glueing styrene to styrene.
Other paints, such as acrylics only form a surface film that physically sticks to the surfaces, rather than through a chemical reaction.
PU resins are an altogether different matter, as they have to be glued together with contact cements or CA cements.
So assembling first or painting first, depends very much on the material combinations that are concerned.
In general, I would assemble parts first that structurally belong together, while details can be stuck on after painting, once precautions as per above are taken.
The cements normally used when working with styrene consists mainly of a solvent and will weld to parts together, rather than act as medium of glue in between them. If parts are painted, the cement cannot work as desired.
A bond is only as strong as the weakest interfaces that are involved. So when you e.g. glue together one or two painted surfaces, the bond will only be as strong as the paint adheres to the surfaces.
Certain paints, such as organic solvent-based enamels (e.g. Humbrol) will fuse with styrene and form a firm bond, but plastic cements do not really dissolve the paints sufficiently to achieve the 'welding' effect, as observed, when glueing styrene to styrene.
Other paints, such as acrylics only form a surface film that physically sticks to the surfaces, rather than through a chemical reaction.
PU resins are an altogether different matter, as they have to be glued together with contact cements or CA cements.
So assembling first or painting first, depends very much on the material combinations that are concerned.
In general, I would assemble parts first that structurally belong together, while details can be stuck on after painting, once precautions as per above are taken.