What is hardboard for, and what is tempered hardboard?

Hardboard is unglamorous and frequently the correct answer. It is the cheapest sheet material there is, it is strong in exactly the way thin panels need to be strong, and modern flat-pack furniture would fall apart without it. The one thing worth understanding is what the tempering does, because standard hardboard and tempered hardboard behave very differently around water.

Step by step

1. Recognise the two faces.One face is smooth and hard; the other carries a fine mesh texture from the screen it was pressed against. The smooth face goes outward on anything visible, and the mesh face is what adhesive keys to.
2. Use it for cabinet backs and drawer bottoms.This is its most important structural job. A thin back panel, fixed all round or set into a rebate, is what stops a carcass racking into a parallelogram. Its thinness is irrelevant because it is restrained on every edge.
3. Use it as a floor underlay before sheet vinyl or lino.Laid over floorboards, hardboard gives a smooth continuous surface that stops the board joints telegraphing through the vinyl. Traditionally laid mesh side up, conditioned first and fixed at close centres with ring-shank nails or staples.
4. Use it as protection and as templates.Temporary floor protection during a job, a template for a scribe or an awkward shape, a bench-top sacrificial surface, a backing sheet under a cutting job. It is cheap enough to treat as consumable, which is exactly what makes it useful.
5. Understand what tempering does.Tempered hardboard is impregnated with oil and heat treated, which makes it noticeably harder, stiffer, darker and far more resistant to moisture. It is the version to use anywhere there is any dampness, and it is worth the small extra cost in a kitchen or a utility room.
6. Condition it before you fix it down.Traditionally you damp the mesh face of a hardboard sheet and stack it flat in the room for a day or two before laying, so it expands to its working size. Fixed dry and then allowed to take up moisture, it buckles into ripples between the fixings.
7. Fix it at close centres.Hardboard laid on a floor needs a lot of fixings — far more than feels necessary — because it is thin and any unfixed area lifts. Ring-shank nails or divergent staples at close spacing, working from the centre outwards.
8. Do not use it structurally.It carries no load across a span at all. It works only where it is fully supported or restrained on every edge. Never use it as a floor surface, a shelf or anything spanning.

Tips

• Perforated hardboard — pegboard — is the same material punched with a grid of holes, and remains one of the best cheap workshop wall storage systems there is.
• Standard hardboard swells and buckles at the first hint of water. In a bathroom, a kitchen or under vinyl in a wet room, use the tempered version.
• It cuts easily with a knife and a straightedge for thin sheets, which avoids both dust and a saw. Score deeply on the smooth face and snap over an edge.

Common mistakes

• Fixing hardboard flooring underlay dry and unconditioned — It takes up moisture from the room and the floor, expands, and buckles into visible ripples that then show through the vinyl. Damping and stacking it flat for a couple of days first is the traditional and effective answer.
• Using standard hardboard under vinyl in a bathroom or kitchen — Any water that gets under the vinyl swells it and lifts the floor. Tempered hardboard or a proper moisture-resistant underlay board is the right choice there.
• Skimping on fixings — Under-fixed hardboard lifts between nails, and every lift becomes a visible bump in the finished floor. Use far more fixings than seems necessary.

Questions people ask