An oil-based varnish is the best choice for this. You apply in much the same way as primer/sealer/paint, with a brush or roller. Other finishes that you can apply to MDF are stain or wax. Stain will typically add a different more natural colour and some sort of fake grain.
Paint the Furniture
If the MDF furniture is currently unfinished, sand the edges smooth and use a solvent-based primer rather than a water-based product to prevent bubbling. Choose an opaque finish in white, black or a bold color such as cherry red for modern or traditional spaces, advises Huffpost.
Seal the MDF with PVA Glue: You can seal MDF surfaces with thin layers of PVA (white or carpenter's) glue. Most PVA-based carpentry glues require dilution with water to get a thin sealing layer on your MDF (which can cause the MDF to swell).
You can use a variety of paints or stains; the trick is to seal the MDF first, then build up layers of paint or stain. Both paint and stain can be finished with a gloss coat to make the MDF look like high-end wood.
MDF can be sealed with polyurethane. MDF, which stands for medium fiberboard, is used for many household applications such as shelves and speaker boxes. It is is easier to work with than regular plywood or particle board.
Unfortunately it won't the MDF will absorb the oil and may distort. I would put a couple of coats of shellac on to seal the MDF then if you want a hard surface a polyurethane.
MDF can be stained, but the finished look is not as nice as natural wood, as MDF does not have any grain to it. Also, because MDF does not absorb stain as well as natural wood, a polyurethane coat over the stain is advisable.
THE APPLICATION OF A VARNISH TO WATERPROOF THE MDF
Simply use a varnish for MDF wood and apply it in 2 to 3 coats with a brush or roller in the direction of the wood fibres. After the first coat of varnish for MDF, lightly grit the surface with 120 grit in order to obtain a perfectly smooth surface.
MDF should always be sealed to prevent moisture penetration. MDF is a composite wood product used in the building industry. The abbreviation stands for "medium density fiberboard." MDF is created by adding glue to wood chips under intense pressure created by hydraulic rams.
You can also create waterproof MDF by adding a high quality wood sealant, varnish or stain or moisture-resistant paint so that your project can withstand threats of moisture and humidity. Do not use waterborne polyurethane, as it may not bind readily to the MDF's surface.
The best paint for MDF board is Oil-based paint. Oil-based paints are common and will work with any solvent-based primer on your MDF. Remember that you need to use paint thinner with oil-based paints. The paint thinner is also used to clean brushes and trays.
Absolutely! You can stain your MDF furniture with dark or light-colored wood stain and improve its appearance. However, the stained MDF piece won't be as well-polished and glossy as natural wood since it lacks wood grain.
Shellac: A natural finish derived from the lac bug, it imparts a warm tone and adds depth to grain. (Drying time: 30 mins) Polyurethane: A synthetic finish made from plastic resin and available in water- or oil-based forms. (Drying time: 2 hours for water-based and 6 hours for oil-based)
For the back I'd just use the same hPL as the face for balance and scuff it up a bit so the fence plates don't slip. Ken, I use shellac on mdf quite often, it is dry by the time you have your brush clean plus it seals it up nicely.
Wipe a thin coat of boiled linseed oil on a piece of MDF scrap and see if you like the result once it's dried. It should darken a bit and leave a pretty slick surface. BLO will provide some protection, and it's easy to reapply to hide wear and tear.
Many people use a traditional workbench finish: a couple of coats of oil (usually BLO or tung oil), but you'll be better off if you use varnish as it is far more waterproofing (and the MDF far more prone to damage from water than the traditional solid wood).
Minwax stain will seal any MDF surface imperfections and leave the board looking brand new. Often times MDF is used for speaker boxes and bookshelves. Having a great Minwax seal will make it look all that much better. Sand the piece of MDF with 120-grit sandpaper.
Best Top-Coat for MDF Fiberboards: MINWAX Water-Based Polycrylic Protective Finish. The Minwax Polycrylic Protective Finish is a water-based product and can be applied to any painted or wood surface.
Whether your MDF project has a factory edge or has been custom routed, the edges must be sealed to accept paint in a way that matches the smoother face of the material. Seal the edges by running a generous coat of drywall compound over them with your finger.