I have used mdf sealer, diluted pva, and acrylic primer for the initial coat, with the main purpose being to seal the mdf prior to the main painting. I think it depends on how much painting you want to do. The mdf sealer gives you a better 'looking' finish when you apply the first coat of paint.
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.
So, if you are wondering if you can make MDF look like wood, the answer is a definite yes! In full disclosure, I implemented this faux wood-grain painting technique with the help of this tutorial from Renovated Faith.
How to use the layering block...... apply a thin layer of paint to the block using a paint brush then run the block over the areas you want to look distressed. This would be the drawer edges, the corners and edges of the chest body, and all of that rippled or bumpy trim.
With so many pieces made of MDF, it follows that they will eventually wear down and become chipped, dingy, or just dated-looking. Fortunately, you can paint MDF and bring these pieces back to life. You can even build new cabinets, shelves, and furniture from MDF and paint them—resulting in a smooth, glass-like finish.
Varnishing the medium is very simple. 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.
It'll need sealing and then plenty of 'high-build' primer, all wet and dried off to get a perfectly smooth finish ready for your topcoat (and, yes, 2k is probably best).
You can use both oil-based paint and water-based paint on MDF. In general, while oil-based paint has traditionally been higher quality than water-based paint, todays technology means that water-based paint is just as good.
Oil-based paints are the most common recommendation for painting MDF. They're reasonably common, and they will be compatible with the solvent-based primer underneath. However, oil-based paints require the addition of paint thinner and the use of said paint thinner to clean up brushes and trays.
Seal MDF Edges Which Are the Most Absorbent
You can use an acrylic paint sealer or drywall sealer, or you can use glue or oil based primers which will help prevent the edges from swelling. Use whichever primer will dry fastest in your particular humidity. The trick is to keep moisture to a minimum.
If the wall is clean and well prepared, chalkboard paint can be applied directly to it. Primer undercoat is the best way to ensure that chalkboard paint adheres well to the MDF first. Using a foam roller, apply the chalkboard paint to the board.
If you like the natural look of MDF and want to add some protection you can use a clear varnish - choose matt or gloss - to keep your MDF looking like new. 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.
You can use varnish or polyurethane to seal the MDF board. Either of these clear coats will do an excellent job protecting the surface and giving it a nice sheen or gloss. What is this? Ensure the stained surface is dry before you apply polyurethane or varnish finish to it.
MDF board is the best material for PU polishing as compare to veneer & plywood.
Medium Density Fibreboard
The MDF primer seals the timber effectively allowing other paints to dry in a uniform way. We recommend painting the timber with an undercoat, after the primer.
MDF can be painted with acrylic paint of any quality. You can apply latex primer and latex paint to large surfaces such as bookshelves or cabinets made of MDF after rolling on a latex primer. You will ruin your hard work if you let any moisture in the MDF.
It should be noted that whichever method you use, MDF is moisture-resistant, not water-resistant, nor waterproof, and is still prone to swelling and warping if in direct contact with the elements.
MDF is quite an absorbent material and typically you will need to apply at least two coats of primer. You may need to apply a third, especially on the edges. After the second coat, rub down lightly with a fine-grade sandpaper -180 grit will do.