Interior and Exterior Paint Sanding Techniques

Painting many interior or exterior surfaces will require some sanding. The objective is to remove surface defects, such as paint runs or heavy build up, and smooth the edges where paint has been scraped.

The end result is a better look and a surface that has better paint adhesion capabilities. The tool list can be extensive.

Power sanders are at the top of this list. Every aspect of smoothing a surface requires effort and good power tools will make this chore much easier.

Two of the best are random orbital and disc sanders. With these power sanders any large area can be smoothed and prepared for painting.

Palm and trim sanders can handle delicate areas that need more finesse. Unfortunately, power tools can't do it all. Smoothing a surface by hand is much easier with good abrasive paper and sponges. This is an essential task in preparing interior wood trim, windows and doors.

Interior Sanding

Interior surfaces should be smooth with ruff paint edges removed, “feathering”, and free of embedded dust. Deglossing a painted surface is also a part of this process.

Existing Painted Wood Trim

Painted wood trim always requires some effort to achieve a smooth finish. If heavy deposits of paint or thick brush lines exist start using a coarse paper or sponge, 60-80 grit sandpaper or medium-fine abrasive sponges will work for heavy deposits.

Use this courser grit to remove most of the heavy areas and brush marks. Finish with 120 grit or the fine side of the sponge.

New Wood

New wood can be smoothed with 120 grit, but finish with 150 grit paper or fine sponges. Always sand in the direction of the wood grain and pay attention to raised grain and mill glaze.

Mill glaze shows up as shiny areas on the wood surface and is produced during shaping or milling. Mill glaze must be removed before staining and can inhibit the adhesion of wood primers.

The final outcome is dependent on this initial sanding.

Use a palm sander or random orbital sander for large flat areas and finish by hand sanding in the same direction as the wood grain. Try to feather, smooth, the edges of peeled paint and loose varnish. Hand sanding is best preformed on stained surfaces, unless a complete removal of the old finish is desired.

Vacuum all the dust and use a tack rag to provide a dust free surface. A clean and dust free surface will produce a smoother finish.

Exterior Sanding

Painted exterior wood surfaces will benefit most from using power sanders. Use either a disc sander or orbital sander on flat siding and trim and palm sander on more delicate surfaces.

A good technique is to use a light touch and work on a large area. Always keep the sander moving on the surface to minimize waves or gouging.

Wood Trim and Siding

Peeling wood trim and lap siding must be hand scraped first then use a power sander to remove any remaining loose paint and smooth the edges. A disc sander can be difficult to use, leaving waves in the wood. This is especially true for soft woods, such as redwood and cedar.

If a more controlled experience is desired use a finer sanding disc, such as 60 grit. For very thick peeling paint use 30 grit discs to cut through and remove the bulk of the loose paint. Then follow with 60 grit sanding discs to produce a smoother surface.

Masonite Siding

Smooth Masonite siding can also be sanded, although this is difficult. Any power sander can be used, but a disc sander or random orbital sander will provide the best results. Use a fine grit, 60 or finer.

Masonite is very soft and old Masonite can be very brittle. Use a soft touch and keep the sander moving at all times. Some waves are inevitable but can be reduced by using a random orbital sander.

Painted Windows and Doors

Windows and doors need a delicate hand. Any and all sanding needs to be done after hand scraping to remove all loose paint, old caulking and putty. Depending on your particular needs start hand sanding with course grit paper to remove any remaining loose material.

The use of power sanders next to glass is problematic and dangerous. The vibrations alone can break glass and scratches can occur from the abrasive paper or disc.

The inexperienced should use a palm sander on windows and an orbital sander on doors. This works great for painted windows and doors.

Stained Windows and Doors

Sanding stained surfaces is virtually the same for interior and exterior restaining. The same attention to smoothness and the possible removal of the existing finish will produce the best results.

Stained windows and doors should be hand sanded with finer paper and sponges. If the finish is in good shape use 180 grit abrasive paper or a fine sponge to smooth any ruff edges or brush marks.

Removing the finish is a bit different. Use 120 grit sandpaper to remove most of the clear finish, and then use 180 grit sandpaper to smooth the remaining stained wood.

Typically sanding paint or stain wood is a multi-step process. Starting with a course sanding grit and progressing to ever finer abrasives until the desired finish is achieved. The amount of actual sanding necessary is up to you and how close to perfection you wish to get. A fresh coat of paint or clear wood finish will enhance any defects, but a perfectly smooth surface will take a lot of effort and time.