Before building a fake fireplace of gypsum board, you are to find proper place for it, draw the design, and make a model. Foam plastic will do nicely for the model. It is light and affordable.
It is better to set your fake fireplace on a pedestal just like you would set a real one. A concrete or a brick pad 20 cm high will do nicely. Find the size of the pad based on the fireplace’s dimensions. The pedestal should be 15-25 cm larger than the gypsum board construction.
Make the frame of metal profiles just like you would make frames for any gypsum board construction. Copy the drawing to the wall and the floor. Then assemble the box using C studs, U channels, wall dowels and screws.
To make the frame solid, make jumpers between the C studs and the U channels. If you need to make an arch, make cuts at 5-6 cm stepouts in the profiles and then bend them.
There’s no need to buy a fireproof gypsum board building a fake fireplace. All-purpose board 12.5 mm will do nicely. They use them to even walls and build bulkheads. If you need to bend the board, use arched gypsum board. It is thinner and can be easily bent.
Do the lining after making sure that the frame is strong enough and is fastened to the walls and the floor. Fasten the board to the frame with screws at stepouts not more than 15 cm. Don’t forget to hide the heads. Prime and putty the ready constructions, then decorate it as you wish.
Decoration is the most interesting part. It lets you make you best design ideas true. To make the fireplace look real use the known parts of real fireplaces like bolts and ash-pans.
You can finish your gypsum board fireplace with any finishing material including natural stone. Don’t forget that heavy constructions require solid base. It is impossible to provide if you live on the upper floors.
Use light materials to avoid overload. Ceramic tiles, artificial stone, decorative plaster and adhesive tape will do nicely. Polyurethane or gypsum plasterwork look unbelievably good.