How to Make a Cultured Stone Arch

Select the smooth arch you wish to attach your cultured stone. It can be indoors or outside. If you need to form an arch from a flat, rectangular ceiling, you need to purchase a mold, create a concrete replica in the shape of the mold, then fit it to the existing structure using concrete mix. Alternatively, employ a professional construction engineer to create an arch by cutting into the existing structure. You may need to seek building regulation advice to do this.

Select pieces of natural stone of similar size, thickness and complementary colors. Cultured stone is usually 1/3 the weight of real stone. A mixture of browns, creams and a few pale oranges or terra-cotta make ideal arch stones. Choose flat, thin stones for narrow arches so they can be laid vertically, or wide, rounded stones for large, wide arches, so they can be laid side-by-side. Place the stones near the planned construction area. Wear a dust mask. Clean the existing stone or plaster with warm, soapy water and a sponge to remove dust and debris. Allow to dry.

Mix concrete powder according to manufacturer's instructions with fresh, cold tap water in a large container, such as a bucket. Add a little bonding agent and mix well. Maintain the temperature of the mixture above 10 degrees Celsius, otherwise the concrete will not cure, or set. Use a trowel to create a smooth mixture that is neither too powdery nor too wet. Add smaller amounts of water to remaining powdery cement using a measuring jug or cup. Aim for a spreadable buttery consistency, not loose or watery.

Place a ladder securely and safely so you can work without overstretching. Apply a continuous, flat layer of freshly prepared cement to the surface of the existing stone and the back of the arch stones using a trowel. Cover a portion of the existing ceiling first and work with that. Create a few rough grooves in the wet cement with the edge of the trowel to fit the two sides together.

Press the arch stones into place. Tap gently to level, using a rubber mallet and a spirit level. The lath should be tight to the existing structure. Reduce any gaps by applying extra cement. If newly added stones remain fixed and do not loosen or break free within one minute of putting them in place, this usually indicates a decent seal has been formed between the two surfaces. Continue until the whole area is complete. Full curing should occur in 4 to 5 days.