Choice of material stove insert

[Fröberg]

Hi, I want to build in a cassette according to the picture. What type of stone should I use?

 

[KnockOnWood]

Leca lightweight aggregate
http://www.gsbyggvaror.se/produkter/lattklinker_betongsten_plintar/LaTTKLINKER.html

Plaster afterwards and paint and it will be great!

//KoW