Glue and grout for Mannequins head and torso

you can use hot glue along -w- your other glue,the hot glue will hold it while the other glue dries,i used tacky glue,when grouting lay your piece propped in a bowl with the part you are working on exsposed this works well for both gluing and grouting,little at a time.

Maybe use a chalk spray paint or something of that type to cover it one that sticks to plastic. Just an idea!

Hi, I am a mosaic artist and instructor, heads are so much fun to do. You should seal your head (substrate) with a couple layers of spray paint or cover it in silver furnace tape not leaving any expose areas. The silver tape is best if using stained glass, it brightens it up.
Sealing any pourous material is important to keep from pulling moisture out of your grout and causing your art to fall apart over time.
Use a good adhesive, Weldbond or clea Liquid Nails for small projects are my favorites. You can also use a clear caulk but I don't like it.
Put your tile (tesserae) on a section at a time keeping small, even grout lines. On a non-flat surface I use painters tape to secure my tesserea being careful to not let adhesive get on it. Remove once adhesive sets. Let your mosaic sit for 24 hours before grouting.
Your grout should be a either non-sandef Ora fine sanded grout.Getting a bag from a home improvement store is cheapest, I get mine at Habitat. Dark colors usually look best. Pool noodles cut into pieces are great for applying and cleaning off grout.
I hope this helps, would love to see your finished head.
Deborah