Wood Types on the Market: Solid Timber, Plywood, MDF and What Each Is For
A joiner builds a kitchen unit, picks a good-looking board, fixes it rigidly, and two months later finds a split along the panel or a swollen edge under the sink. The workmanship was fine; the material choice was not. Wood is not one substance, and each type has behaviour you must respect before you cut.
1. Solid Timber and Its Constant Movement
Solid timber is sawn from the tree and dried. Commercially it splits into two groups:
- Softwood (pine, fir, spruce): light, easy to cut and fix, used for framing, formwork and hidden work.
- Hardwood (oak, beech, walnut, mahogany): denser, stronger, better figure, used for furniture, doors and wearing surfaces.
Grain Direction and Moisture Movement
Timber absorbs and releases atmospheric moisture, so it swells and shrinks. The movement is not equal in all directions: movement across the grain is significant and measurable between summer and winter, while movement along the grain is negligible.
That is exactly why solid panels crack. Fix a wide solid panel rigidly on all edges with glue and screws into a frame that prevents movement, and the panel tries to expand, cannot, builds internal stress and splits. Traditional joinery solves this by letting panels float in grooves, or by screwing through elongated slots so the panel can move across its width.
2. Plywood and Why It Stays Put
Plywood is thin veneers glued with each layer's grain at right angles to the one below. That cross-lamination is the whole point: a layer wanting to expand across its width is restrained by its neighbour's length. The result barely moves with humidity and carries strength in both directions. Layer counts are odd so face and back grain run the same way and the board does not cup.
- Interior grade: non-water-resistant glue. Fine for dry-area furniture; it delaminates under sustained moisture.
- Moisture-resistant and marine grade: water-resistant adhesive, fewer veneer defects, fewer internal voids. Suited to bathrooms, splash zones and exposed work.
- Face grades: classified by freedom from knots and patches. Clean faces for visible surfaces, lower grades for hidden or covered work.
3. MDF, Chipboard, Blockboard and Melamine
MDF
Fibres broken down completely and pressed with resin, giving uniform density with no grain or knots. Its advantages: a very smooth surface that is the best substrate for painted work, and clean routed edges that do not splinter, which makes it the natural choice for painted doors, mouldings and carved detail. It is also dimensionally stable.
Its weaknesses are real. Water is its enemy: wetted fibres swell permanently and do not recover on drying, so it has no place under sinks, in wet bathrooms or outdoors unless it is a moisture-resistant type with every edge fully sealed. It also holds screws poorly in cut edges, which crumble under screw pressure. Edge fixing needs an accurate pilot hole and screws made for board materials, and ideally knock-down fittings that spread the load instead of a bare screw. Its dust is very fine, so wear a mask and use extraction.
Chipboard / Particleboard
Coarse chips pressed with resin. Lighter, cheaper and weaker than MDF, not suitable for direct painting, usually supplied faced. More moisture sensitive, weaker screw hold, and visibly saggy over long spans.
Blockboard
A core of solid timber strips laid lengthwise, veneered both faces. Light for its thickness, strong along its length, good for doors, long shelves and surfaces needing stiffness at sensible weight.
Melamine-Faced Boards
Chipboard or MDF faced with resin-impregnated paper under heat and pressure. The surface is finished, scratch resistant and wipeable, needing no paint. The cautions: cut edges are exposed and need edge banding, and cutting needs a fine-toothed blade and the right feed direction to avoid chipping the facing.
4. Comparison
| Material | Stability | Moisture resistance | Screw hold | Paint | Best use |
|---|---|---|---|---|---|
| Hardwood | Moves | Good if finished | Excellent | Good | Furniture, doors, wear surfaces |
| Softwood | Moves, cups | Moderate | Good | Moderate | Framing, formwork, hidden work |
| Interior plywood | High | Poor | Very good | Good with edge prep | Carcasses, backs, bases |
| Marine plywood | High | Good | Very good | Good | Bathrooms, kitchens, exposed |
| MDF | Very high | Very poor | Poor in edges | Best | Painted doors, mouldings, routing |
| Chipboard | Good | Very poor | Poor | Not direct | Faced, non-loaded work |
| Blockboard | Good | Moderate | Good | Good | Doors, long shelves |
| Melamine | As core | Face good, edges weak | As core | Not painted | Cabinets, internal shelves |
5. Choosing by Application
Kitchen carcass: moisture-resistant plywood, or melamine on a moisture-resistant core in dry zones. Sink bases and washing-machine surrounds deserve moisture-resistant plywood with fully sealed edges, because a small leak destroys chipboard or standard MDF.
Painted doors and fronts: MDF wins outright. Seal every edge with primer before topcoats, since an unsealed edge drinks both paint and moisture.
Shelving that must not sag: sag is governed by span and thickness more than by material. At equal thickness, best to worst: hardwood, blockboard, plywood, MDF, chipboard. The strongest practical fixes are shortening the span with a centre support, or fixing a timber lipping to the front edge to increase structural depth.
Outdoor work: chipboard and standard MDF are excluded. Use timber treated for external use or marine plywood, with a finish renewed periodically and a design that drains water rather than trapping it in corners.
6. Fixing Notes
- Solid wood: pilot drill near ends to prevent splitting, and allow cross-grain movement.
- Plywood: good face screw hold; pilot drill edge fixings to avoid delamination.
- MDF: pilot holes mandatory, slim-core screws, and no high torque or the thread strips.
- Chipboard: use knock-down fittings and inserts rather than bare screws where possible.
- Melamine: cut with fine teeth and seal cut edges to protect the core.
Conclusion
No wood is best in the abstract; each material has its place. Ask three questions before buying: will it meet water, will it be painted, and what span will it carry? Those answers almost fully determine the material. And respect the rule many people pay for twice: solid wood moves, so let it, while fibre-based boards swell in water, so seal their edges and keep them dry.
