Plaster coving is an elegant accent that can enhance the atmosphere of any room's decor. Unfortunately, buying finished plaster coving can be a very expensive proposition. Plaster may be messy, but constructing your own plaster coving can take hundreds of pounds off of your home remodelling budget. You'll also appreciate the intricate design you created more than the store-bought manufactured design. Allowing proper time for cleanup, this project can take place in the course of one afternoon.
Measure the area you want to cover with plaster coving. For arc-shaped coving, find the arc's radius. Measure the length between the two bottom corners of the arc. Measure the height from the centre of that distance to the top of the arc. Using a calculator, divide the length by 2 and then find the square of the result. Divide that sum by the height. Add the height to that result. Divide that sum by 2 and the answer is the arc's radius.
Lay a tarpaulin out flat onto a work bench. Draw two parallel lines with your black marker, indicating the coving length found in Step 1 and the desired coving height. For arcs, make two marks indicating the bottom corners of the ark. Mark the centre point between those corners. Begin to measure away from the centre the distance of the radius. Create the arc's path by marking the radial distance at points from one corner to the other. Make a new mark every inch or so. When finished making this dotted line, use your marker to connect these dots with a solid line. Create the upper line of the arc by adding the desired coving height to the arc's radius and repeating this process.
Trace the desired profile of the coving onto two blocks of 1.8 cm (1/4 inch) plywood with a pencil. Use plywood that is a few inches larger than the coving height. Cut out the profile on both blocks using a scroll saw.
Place a thin piece of aluminium sheeting between both blocks. Line up the cut profiles so that they are in the same position. Secure the aluminium sheeting and plywood with a cordless drill and 3.1 cm (1 1/4 inch) screws. Cut out the coving profile on the aluminium sheet on the scroll saw, using the plywood as a guide.
In a bucket, make a mixture of the plaster dry mix and water. Use the directions on your plaster dry mix package for proper ratios of plaster to water.
Load the plaster onto the tarpaulin with a trowel while still pliable. Keep the plaster between the two marker lines and fill the entire length.
Put on work gloves if you haven't already. Grab the aluminium coving profile, also known as a screed, and begin to drag it across the length of the coving. Use the trowel if you add additional plaster to any bare spots, or to drag excess plaster away. Let the plaster coving sit to dry.
Use caution when mixing plaster. Plaster heats when it reacts with water and can cause burns.