How to install a heated towel rail
Drill holes in the corners of the square you're cutting out for the sump to fit into. This'll make it easier for you to cut out. Put on your safety glasses, gloves and ear muffs and use the angle grinder to cut out the square in the fibre cement board. If you need to, use a hammer and chisel to help you remove the fibre cement board. With your battery powered saw, cut the next layer of flooring. You may need to use a handsaw to complete the cuts to the corners. Lift this piece of flooring out. You may also need to use the handsaw to cut any under-floor insulation that might be there.
Lay the shower base on the floor and outline its height on all of the wood that it leans up against. Remove the shower base. The pencil mark on the wood is the top of the recess that the shower base will fit snugly into. Use a hammer and chisel or a handsaw to cut away the wood to make 10mm recesses for the shower base. You'll also need to make a 10mm recess in the timbers running across the length and width of the shower base. Do this by marking out 10mm in from the edge and use a hammer and chisel to cut the wood. Wear gloves when you mark this wood to protect against splinters.
To make your cement, mix three parts of brickies sand with one part mortar in a wheelbarrow. Slowly add water to the mixture and combine them using your shovel, so that it's not too thick and not too runny. Continue mixing until the concrete has a uniform consistency and texture and there are no pockets of dry material.
Use your shovel to lay the concrete base on to the floor, so that it will cover all of the shower base, which will give it a solid foundation. If you need to, add extra concrete in the areas where it is needed so that the shower base is level when you put it into place.
Lay the shower base on top of the concrete and wriggle it into place and sit it snugly in the recesses you cut out. Once it's in place use your spirit level to make sure its level. If it isn't move it around until it is. Use your shovel to clean up all of the excess cement around the edges of your shower base.