Which varnish should I use — polyurethane, acrylic or yacht?

Varnish is a resin that cures to a continuous film on the surface. That is its strength — nothing protects wood against water, heat and abrasion as well as a film — and its weakness, because when it wears through it does so with a visible edge, and the honest repair is to strip and recoat rather than to patch. Within that, the resin type decides everything else.

Step by step

1. Oil-based polyurethane — the interior workhorse.The toughest common interior varnish, with good heat, water and abrasion resistance. It ambers the timber noticeably, which suits oak and pine and does not suit pale woods, and it goes on yellowing with age. Slow drying, strong solvent smell, and it lays off beautifully with a brush. This is what interior floors and stair treads should be finished with unless there is a reason not to.
2. Water-based acrylic varnish — clarity and convenience.Dries in a fraction of the time, so several coats in a day, very low odour, cleans up in water, and — the real point — it does not amber. On maple, ash, birch or a light-stained finish it keeps the colour you sanded to. Slightly less abrasion-resistant than polyurethane, and it raises the grain on the first coat.
3. Exterior wood varnish — flexibility and UV protection.Formulated to move with timber through seasonal swelling and shrinking, and containing UV absorbers to slow the breakdown that destroys clear finishes outdoors. Use one designed for exterior joinery on doors, frames and garden furniture.
4. Yacht varnish — a specific product widely misused.It is formulated to stay flexible on a hull that flexes and gets soaked, which means it stays softer and marks more easily than an interior varnish. It is not a super-durable general varnish and, crucially, many yacht varnishes have little or no UV protection, so on a south-facing door they break down quickly. Use a proper exterior wood varnish instead unless you specifically want flexibility.
5. Choose the sheen last.Gloss, satin and matt are the same resin with flatting agents added. Gloss is marginally the toughest and shows every defect; satin is the usual choice; matt shows the fewest marks. On a multi-coat job, several coats of gloss with a final coat of satin gives both durability and appearance.
6. Match the varnish to what is underneath.Water-based varnish over an oil stain that has not fully cured will not adhere. Anything over wax will not adhere at all. Over an oil finish, nothing sticks reliably until the oil is genuinely cured. Shellac is the traditional isolating barrier between incompatible layers.
7. Plan for how you will repair it.Varnish is not patched invisibly. On a floor that will need refinishing eventually, that means sanding the whole floor. If local repair matters more than maximum protection, a hardwax oil is the better system.

Tips

• Thin the first coat slightly, as the tin directs, so it penetrates and keys into the timber rather than sitting on top. It makes a real difference to adhesion.
• Water-based varnish raises the grain on the first coat. De-nib after it, and subsequent coats stay smooth.
• Floor varnish and furniture varnish are formulated differently for abrasion. Use a floor product on a floor, not a general-purpose one.

Alternatives

• Hardwax oil: Less outright protection than polyurethane, but repairable in patches without stripping. The right answer on floors and worktops where local repair matters.
• Two-pack lacquer: The most durable finish available for timber, used commercially on floors and cabinetry. Needs mixing, has a short pot life, and is generally a job for a professional.
• Shellac or French polish: Beautiful on antique and period furniture and easily repaired, but it is damaged by water, alcohol and heat, so it belongs on pieces that are looked at rather than used.

Questions people ask