Fake stone picture frame from XPS foam for a puzzle

In this article, we build a fake stone picture frame for a Marvel puzzle.

My kids and I really enjoyed finishing this marvel puzzle and were looking for a way to hang it on the wall.

CNC work in XPS foam

From a recent renovation project we had some leftover XPS foam. We used the CNC to make a special frame but the material is also easy to shape with a handheld router or a Dremel.
The CNC program is created in FreeCAD and rather simple. After a facing operation the CNC removes a bit more material from the area where the puzzle will be mounted so that it sits flush with the frame. Next we cut a groove all around the perimeter and cut the form free leaving tabs that hold the foam in place.

The surface finish of the CNC is a bit rough so I sand all visible parts of the foam smooth.

With a ball of tinfoil I give the frame a bit of structure by rolling it over the frame.

Painting a fake texture to create a stone picture frame

To protect the soft XPS and cover the green color I mix PVA glue with black acrylic paint.

This mixture is then applied to the frame and creates a hard surface.

With a piece of a kitchen sponge I apply some white, brown and mud-like color.

After these colors have dried I cover most of the color with a light grey. By applying the grey with a sponge not all the areas are covered and you get a pattern that looks similar to stone with inclusions.

Mounting the puzzle

While the grey color is drying let’s take care of the puzzle by first sliding a sheet of parchment paper under the puzzle to protect the table.

I apply a few coats of PVA glue thinned down with water so that it’s easier to spread it with a roller. The glue dries hard and transparent. It also creates enough of a bond to move the puzzle as one piece.