Just about any kind of knife, Find one you can use with comfort,and hack away.
Don't worry about what itlooks like, You will have to make it nice with somthing, I use dry wall mud.
As Mr. B stated; cutting a grid, and knocking out the chunks works well.
Ringo58What would be the best way to carve out the foam.
I bought one of these, a surform, and I used it a lot with my foam layout. I got one of these for about $7.00.
Also, a shop vac might become one of your best friends.
York1 John
I use player cloth, paint and Envirotex for water areas. They don't have to be very deep.
I cut a grid pattern in the foam, only a half inch deep or so. Sliced up like that, the foam is easy to carve out with a spoon. The resulting surface is rough, so I go over it with plaster cloth to produce a better lake or river bed. I usually go over the plaster cloth with white glue to seal the cloth so the Envirotex doesn't seep through all the little holes.
It takes an iron man to play with a toy iron horse.
I want to add a small water feature on the layout. I was thinking a small stream. I want it ro run under the main, then under the siding by the warehouse and dissapear under the gas station ( realistic to my town has a small stream that runs under a gas station and a car dealership before it comes back out). What would be the best way to carve out the foam.