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Installing molding requires accurate measurement and precise joints, and securing it neatly can be difficult. The makeup of a wall defines the method. Molding may be joined with mitered cuts at internal and external corners; internal corners can also be done with profile cuts. Molding may need cutting to keep it level on an uneven floor, and this will involve scribing, a method of accurately marking and cutting a board to fit exactly the profile of the floor on which it is being positioned.
Before attaching baseboards, establish whether the wall is lumber, masonry, or drywall. Use the relevant fastening method from those shown below. If you are attaching molding to a stud wall, establish first where the studs are — you will need to secure the molding at these points. If you are building a new stud wall this is not a problem.
Vertical cracks in plaster, or lines of nail heads may indicate edges of drywall — and, therefore, studs. Otherwise, use a stud detector, or simply tap the drywall until you don’t hear a hollow sound. Once you have located one stud, look for others at (usually) 16-inch intervals. Use a cable/pipe detector to avoid wires and pipes.
Apply glue to the back of the molding and place in position (Image 1). Use a masonry drill to make two pilot holes every 1 foot.
Enlarge the openings of the holes with a countersink bit (Image 2). This will allow the screw heads to sit below the wood's surface.
Screw the boards to the wall (Image 3). Fill the countersunk holes with filler, if necessary, and sand.
Apply some grab adhesive to the back of the molding, and place it in position (Image 1).
Attach the molding with two screws or finish nails at each stud (Image 2). Studs are usually 16 inches or 2 ft apart.
If possible, locate studs and mark their positions. Apply grab adhesive to the back of the molding, and position the board.
Attach the molding to the studs at regular intervals with two screws or finish nails. If you cannot locate studs, attach at regular intervals.
Mitering gives neat joints in a corner or between lengths on a straight run along a wall. A miter box is an alternative to a power miter saw — but it is difficult to get accurate cuts, and most boxes will not hold the tallest boards.
Make sure you cut in the correct direction; mitering angles differ for internal and external corners.
The easiest way to make a mitered cut is with a power miter saw (Image 1). If the saw has the height, a board can be clamped upright and cut down through its height. In this instance, it is laid flat on the stage of a miter saw. Larger boards are best cut this way. Tilt the blade and cut a 45-degree angle in the board.
Repeat for the joining board, and fit the pieces together in the corner (Image 2).
Cut miters as before. Check for fit. Place one board (Image 1). Apply wood glue to the cut end, position the other board, and wipe away excess glue.
Drill pilot holes for two brad nails to fit through the mitered joint and hold it together. Pin the corner (Image 2).
Mitered joints are neater than butt-jointed boards. Cut the ends at a 45-degree angle, checking that they will fit together when attached (Image 1).
Glue the boards into place, and hammer in a brad nail to secure them (Image 2). Attach the rest of the baseboard as normal.
Butt one piece of molding against the wall and cut the other piece to fit exactly against the first (Image 1).
Using an offcut of molding, draw around its profile on the board that needs cutting (Image 2). This forms a guide line to cut along with a jigsaw.
Having cut along the guide line (try a hand-held coping saw or a fret saw if the molding is too ornate to cut with a jigsaw), butt the cut end against the first piece of molding (Image 3). It will exactly match the profile and give a neat finish. Fix the molding in place and continue fitting the molding around the room.
Undulations in a floor can leave unsightly gaps below molding, which can let in drafts. It is always best to ensure that the top edge of the molding is level, and to trim any necessary adjustments from the bottom edge. In some cases, a slight slope may be acceptable, as long as the joint with the floor is flush. Minor gaps at the bottom may be covered with carpeting, the edge of a wood floor, or a decorative molding.
Cutting off a section from the base of a length of molding may mean that neighboring sections also require trimming, even if they sit flush with the floor, otherwise they may be taller. Therefore, cut all pieces to length and loosely position them all (as described in the next step) to find the right height for all boards.
Position baseboard against the wall, and use a level to check if it is level at the top and flush with the floor (Image 1). If not, scribing is needed.
Wedge the molding so that it is completely level — check this with the level (Image 2). Use a temporary fastener to hold it if required.
Cut a small piece of wood that is slightly taller than the biggest gap between the molding and the floor. You can use this as a scribing block. Place a pencil on top of it, and slide the block and pencil across the floor surface, so that the pencil marks a guide line on the molding matching the profile of the floor (Image 3).
Use a jigsaw to cut away the excess molding, following the pencil line carefully (Image 4).
Fix the length of molding in place. It should be flush with the floor and level along its length (Image 5).
Excerpted from Do It Yourself Home Improvement
© Dorling Kindersley Limited 2009
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