Step 1- Use a pipe and cable detector to check the area where you are fitting it is clear.
Step 2- Draw marks 6mm from the inner edge of the door casing, down both sides and across the top
Step 3- join the marks using a straight edge or spirit level
Step 4- Measure the line across the top of the door, make sure to leave enough room at either end to allow for mitre cuts and lightly mark
Step 5- Place the architrave flat side down in the mitre box, and use a fine tooth saw to make two 45-degree mitre cuts. They need to be angled in opposite directions, so the outer edge will be wider than the inner edge on both sides of the door
Step 6- lightly sand the cut ends until smooth. Following the manufacturer’s instructions apply grab adhesive to the back of the architrave.
Step 7- Fix the head piece into position using the 6mm guide line using the adhesive sets, hammer and four evenly spaced 40mm lost head nails.
Step 8- measure from the bottom of the head piece to the floor and mark the distance onto the two sections of architrave that will be your side pieces
Step 9- Mark the direction of the mitre cuts on both pieces, make the 45- degree cut to each side piece (make sure they’re in opposite directions) and lightly sand
Step 10- Test the mitre joints before fixing, and if needed make suitable adjustments
Step 11- Apply some PVA glue to the mitre cut at one end of the head piece, and the corresponding side piece. Apply some grab adhesive to the back of that side piece and fix into position with six evenly spaced 40mm lost head nails
Step 12- Repeat step 11 for the other side
Step 13- use a hammer and nail punch to sink all the nails to just below the surface, then fill and sand the nail holes before painting