the painted surface
How To Paint A MDF Bookcase
Medium density fiberboard is used in many applications, some being MDF interior trim for woodwork, shelving for closets, wainscoting and other uses. MDF is cheaper than solid wood products, provides a very smooth and flat surface and accepts paint very well. If moisture may come into contact with the product make sure the MDF is water resistant, some grades of MDF are not and can be difficult to repair if they should become wet. It is heavier than most wood. MDF shelving should be stiffened by attaching a piece of solid wood across the front of the shelf. This will also protect the edge from dings and dents. Paint products normally used for wood surfaces are appropriate for MDF. Water-based products may cause some raising of the fibers on edges and ends of the boards. These are usually easily sanded smooth. MDF can be the perfect product for your project.
Preparing To Paint A MDF Bookcase
This bookcase was built using a variety of wood products. The second photo shows four types used, paint-grade clear pine for the crown moulding, poplar for the face frames and stiffeners for the shelves, preprimed plywood beadboard for the back and medium density fiberboard for the shelves and casework. Although different wood products are used, the same paint can be used on each surface. The preparation of the surfaces might vary slightly however. The solid wood can be sanded if needed to smooth the surface. The cut edges of the MDF should be sanded with progressively finer grits of sandpaper to smooth and polish the edges. If these edges are left rough the painted finish will not be smooth. But I would not sand the face of the unpainted MDF, it is layered with a paper that can be easily scarred with sandpaper. If the mdf is damaged, prime the surface first, allow it to dry, apply the patching compound, allow it to dry and then lightly sand the damaged spot until smooth. The preprimed beadboard should be smooth and ready to paint but I recommend to prime it with the same primer used on the bare surfaces to achieve a consistent base for the finish coats.
The first thing I like to do is to thouroughly vacuum all the surfaces of the project. Wood and especially MDF is dusty when cut. A good shop vac can suck out the small particles from cracks and crevices. These bits of wood can really mess up the finished surface. To go the extra mile to remove the dust use a tack cloth to wipe over the entire surface to remove the ultra fine dust. A tack cloth is found at your local hardware store with the painting and staining products. It is sticky(tacky) and will pick up very fine dust.
How To Prime A MDF Bookcase
Primers used for MDF are the same as those used for bare wood surfaces. They should seal the surface, especially the edges of the MDF boards which can be very porous. The primer should be compatible to the finish paint so the two will bond well together. The primer can be tinted to be similar to the finish color which might improve coverage. The primer should be easy to sand when dry. An oil-based enamel undercoater will give satisfactory results.
When the primer is dry you will probably see some cracks that will need to be filled to improve the appearance of the project. Now is the time to caulk and repair any imperfections in the surfaces. Caulk adheres better to a primed or painted surface than bare wood so it is best to prime first and caulk second. Use an acrylic caulk to fill the cracks around joints and seams. Some more information can be found in the article "How to Caulk".
Any other imperfections can now be repaired. These might include nail holes or dings in the surfaces. If their are any stains or wood sap bleeding through give them another coat of primer. If they still bleed through use shellac or a shellac based pigmented primer to seal them.
How To Sand A MDF Bookcase
After the caulk is completely dry which may take several hours or overnight the surfaces should be sanded. Sanding is not fun but the rewards make it worth it. This project was built with finish grade products so only a light sanding is needed. Also the cut edges of the MDF was sanded prior to priming to smooth them as much as possible. The primer when dry is slightly gritty but this is easily smoothed with light sanding. Sanding sponges are great for this project. They come in fine grades and are flexible enough to sand the curved mouldings while flat and durable to sand the flat surfaces.
If possible, place a fan in the window to help exhaust the dust and always wear dust protection over your nose, mouth and eyes. Sand the entire project, the surface should feel fairly slick after only a couple of passes with the sanding sponge. Be careful not to sand through the primer to the bare wood.
The sanding was done on the second day of the project. Waiting overnight allowed the primer to dry and the caulk to firm up.
The sanding will once again produce a fine dust that should be vacuumed and wipe off with a tack cloth. This article is continued on page 2