Searching the web for information on how to coat EPS foam mainly for crown molding resulted in almost NOTHING.
So I decided to share my experience with everyone.
Coating foam with cement is usually used in the building industry, crowns, crown moldings and other shapes need to be coated in order for the stucco to adhere to the cement coat, and provide strength to the parts.
1st step is to acquire a bag of "foam tite" this material is very similar to regular cement but has some glue additive to help it to stick to the foam. Mix the correct amount of water as directed on the bag.
2nd step is to place the foam on a flat surface - in this example we took an old table, for best results, cover the table with plastic bags, that way cleaning up is much simpler.
3rd step: cover the foam with some kind of mesh, in this example we used a regular fiberglass mesh that can be found in HomeDepot. The mesh that we used has a self adhesive glue, so it will stick to the EPS foam.
There are different meshes out there and some do not have the glue, if you use the mesh without the glue, you will need to glue the mesh to the foam, this can be done with 77 Glue from 3M.
Try to keep the mash as tight as possible and as smooth as possible avoiding air bubbles.
It is also good to buy "virgin foam" not recycled foam. Recycled foam can cause vibration on the wire which will show up on the foam as lines across the foam.
Next step is to coat the foam with the "foam tight" - simply take a handfull of the material and cover the foam (by hand)
The next step is to remove all the excess material. In this example we made a template that is about 1/8" larger then the size of the part we are covering
Move the template all the way to get an even coat on the foam.
Let dry the 24 hours and apply a 2nd coat if needed.
Looks simple and it is, but be prepared for a short "learning curve" over time you will see that its just a matter of experience, the more you do it the faster and smoother the parts will be.