Painting is a common finish for timber and can be applied to raw MDF with spectacular results.
Painting is a common finish for timber and can be applied to raw MDF with spectacular results. It does, however, require significant preparation and correct surface treatment to work well and results will vary considerably depending upon methods used. If you have never painted MDF before then be prepared for a challenge, perfect results can be acheived but usually only by those with some prior experience.
Remember, the higher the gloss/darker the colour the more preparation work is required.
If you have not painted MDF previously we do NOT recommend trying a gloss black finish as your first project!
MDF is extremely porous and must be sealed to prevent paint soaking into the MDF. There are a wide range of products available to achieve this purpose and many woodworkers have personal favourites. The two common ones that The Loud Speaker Kit has used to good effect are any one of the many "MDF Sanding Sealer" type products sold through hardware stores which is sprayed or brushed on, or an automotive "Spray Putty/Primer" sold through automotive outlets and some hardware stores. The sanding sealer prevents paint from sinking into the surface but cannot improve a damaged or uneven surface. The primer/putty can be applied in multiple coats to build up a surface.
Primer putties can be sourced in 1 pack, 2 pack, acrylic or enamel bases and you should read the manufacturers instructions and warnings carefully before use. Generally speaking, the single pack acrylic bases are the easiest and safest to work with whilst the 2 pack products yield the superior result.
Preparation is the single most important step in the painting process. If you want to achieve a superior result you need to plan this prior to assembling the cabinet. The use of multiple wood clamps to minimise any gaps on the seams of the panels is highly recommended. Once you have assembled the cabinet and it has dried you may need to fill any remaining gaps with a standard wood putty or automotive "bog" product. Even a "hairline" crack will cause problems with the top coat and should be removed. The spray primer/putty cannot fill cracks or seams.
One technique that is successfully used by customers who want to achieve that high gloss piano black finish is to fill all of the cabinet seams (the joins between two panels) with an automotive "bog" or body filler. This is basically a heavy liquid putty that goes on before the primer/putty and is applied with a spatula. Once dried, you sand almost all of it off the cabinet and it fills the seams nicely.
Once you have filled any major gaps in the cabinet you need to sand the MDF to prepare for the primer/putty undercoat. Sand with 180 grit paper and ensure there are no high spots or ridges showing. At this stage you might choose to slightly round over all the edges of the cabinet with the sandpaper, this can give the box a more pleasing appearance and helps protect the corners and edges from chipping easily.
Spray or paint on an initial coat as per the manufacturers instructions.
Once the first coat has dried, carefully sand it back using a 320 or finer sandpaper. For the best results, use 600 grit wet&dry sandpaper but be prepared to work hard! Once the first coat is largely sanded back (bare MDF is often visible in several places on the cabinet) spray a second, lighter, coat. Sand this back too, using progressively finer grades of sandpaper until the primer putty undercoat is smooth and silky to the touch with no pits or seam lines showing.
M7 kit with undercoat (yellow) and partially sanded topcoat
For a superior result you should sand with at least three grades of paper, 400, 600 and 800 or even higher (finer) wet & dry. The more effort you take here to get the primer surface perfect the better the end result.
It is not uncommon for some customers to do as many as 6 coats of primer putty to acheive a dead flat finish!
Using a tack-cloth (or a clean lint free rag) carefully remove all traces of dust from the cabinet. For superior results, dampen the rag in a "prep wash" or "wax and grease remover" solution available from paint supply stores which will ensure all traces of wax and grease are removed.
Carefully spray the first top coat onto the box, working from the top down. Use multiple light coats rather than one heavy coat for best results. To spray all 6 sides at once, you can suspend the box from a bracket made from stiff wire such as a coat hanger. Place this through the cutouts in the front of the kit so that it does not contact the outside of the cabinet at all. Alternatively, you can simply spray 5 sides and then, once dried, mask them off and spray the remaining panel.
Note the use of a proper respirator and spray booth
For superior results, sand this first coat back using 600 grit and then repeat a second or even third topcoat. Many customers who work in the automotive industry advocate using a clear topcoat, especially when over black paint, and some will mix 50% clear with 50% black (or whatever colour is being used) to provide a hard wearing high gloss finish.
Allow the paint to thoroughly dry before fitting the speaker drivers. Many of the solvents used in paints are harmful to the glues used in driver voice coils so we recommend you leave the cabinets in a well ventilated place to air out for at least 24 hours before final assembly.
M7 kits drying
The finished product
One interesting product that is available on the market from larger hardware stores is a range of textured paints in spray can form. One of these, "Fleckstone" has been used by customers to achieve an interesting range of finishes. A benefit of the textured surface is that surface imperfections are masked and little or no preparation to the kit is required to achieve a great result.
To use Fleckstone as a topcoat, spray the box with a cheap primer paint in a similar colour to the chosen Fleckstone and once dry, *lightly* spray the topcoat evenly over the speaker. Be warned, this makes a mess of nearby surfaces!
Grey Fleckstone topcoat over grey undercoat
To use Fleckstone as an undercoat, first undercoat with a basic primer paint as above, then apply the Fleckstone. Then apply a topcoat colour (usually a flat colour like matt black as shown below) for a great hard wearing textured finish.
Black topcoat over textured undercoat
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