Mark the quirk or step (distance between inside edge of window reveal and inside edge of the architrave, normally 5mm, but may vary depending on client requirements) on all corners as well as at intervals between corners. These points are used for measuring the short lengths of architrave as well as a guide for positioning inside edge of architrave when nailing in place.

Measure the distance between corner quirk points which represents the short length of your 45 degree mitre cuts. We are installing the right side architrave first and then working around the window in an anticlockwise direction

Cut a 45 degree mitre cut on both ends of a piece of architrave and add 5mm to the distance measured on step 2.

Position the architrave so the bottom 45 degree mitre cut is held in relation to the bottom quirk intersection point and then remark the top intersection quirk point.

Trim the top 45 degree mitre cut so it meets the top quirk intersection point exactly and nail in position. Nail into the window reveal first, keeping the inside edge of the architrave parallel with quirk points and then nail to plaster and timber framework behind.

Repeat steps 2 and 3.

Position right end top 45 degree mitre cut in position, keeping it in line with the quirk points and maintaining the inside edge parallel with the top window reveal. Press top right mitre cut down firmly against the side top mitre cut and observe how neat the fit is. If there is a slight gap on inside or outside of the 45 degree mitre cut, then re-adjust the mitre saw and recut to make the mitre joint a neat fit.

Position the right end of the top architrave neatly against the side architrave that is already fixed in place and then mark the left quirk intersection point and trim to length.

Apply PVA glue on the right end of top architrave and position and nail in place as per Step 5.

Wipe off excess glue from the corner mitre joint with a damp cloth. Repeat steps 6 to 10 with the last two pieces of architrave to complete the installation. The architrave is now ready to sand and paint.

Place curved head architrave in place and pin, allowing for a quirk or step off reveal edge (typically 5mm). Trace around the inside and outside edge of curved architrave.

Place two side upright architraves in place and pin, allowing for 5mm quirk or step. Trace around inside and outside edges of both upright architraves. Take particular care where the line tracings intersect with the curved head lines.

Remove the upright architraves, and the trace lines will be left on the wall. Draw lines connecting the intersection points of the curved and the straight lines. The angle lines may then be transferred onto the architraves by two options:

a) using a sliding bevel or a combination square; or

b) pin the curved architrave in place. transfer the intersection points to the inside and outside edges of the architrave. Join these points to form the angle to be cut. Repeat this process with the top of the straight upright architraves.

Trim the architraves to the lines marked on them and install.