What glue should I use to fix real coal in my OO gauge locomotive tenders?

Adding real coal to a OO gauge locomotive tender enhances the realism of a locomotive massively compared to the injection moulded, artificial coal that comes as part of the tender moulding.

The good thing in many cases is that you don't have to actually remove the plastic coal moulding in order to do this. There's usually just enough room to add a layer of real coal on top. But the question is, what glue should be used to hold the coal in place?

PVA or a propriety ballast glue such as Deluxe Materials Ballast Bond will do the trick. Both set with a matt finish so they're virtually invisible once dry. And both are easy to work with. 

• For PVA, simply spread a good layer of the adhesive over the plastic moulding to be covered and sprinkle on a layer of crushed real coal and allow it to dry. 
• For Deluxe Materials Ballast Bond, apply the coal first, using an old paintbrush or your finger tip to arrange the coal how you'd like it. Then sprinkle a generous coat of Ballast Bond over the coal then leave to dry thoroughly.