How To Paint Wood – Filling Cracks and Sanding Down Wood

Dents, cracks and chips must be filled or they will show through the new paint. But before you reach for the filling knife, it’s worth taking a moment just to check the problem.

Sometimes, blemishes in the paint coat can indicate a fault in the underlying woodwork. Two things to watch out for are cracks caused by loose joints, and splits caused by damp. Window and door frames are particularly prone to the first problem — generally it shows at the corners of the main frame. The second can occur almost anywhere — but particularly on outdoor woodwork and in kitchens and bathrooms.

filling cracks in woodThere is no point in trying to fill over either of these. If a joint is weak, it will almost certainly be subject to further movement — reopening the cracks. If you fill over a damp problem, the rot will go on working inside the wood — probably to recur later.

  • So make repairs first. Strengthen the joint or rebuild the frame.
  • Cut out damp and dirt back to sound, dry wood.
  • Prime the bare wood and allow to dry.
  • Then fill the holes with any general-purpose cellulose filler.
  • If the hole is particularly large, don’t try to plug it in one go — the filler will take ages to dry properly, and may not dry at all. Instead, apply it in layers about 5mm thick, allowing each to dry before building up the next.
  • For small blemishes you can get a better finish with a fine surface filler, which is smoother and easier to spread.
  • Sand the dried filler flush with the surrounding surface.
  • If there are any scratches or pits in the filler, you can smooth these with the fine surface type.
  • Finally, prime the area with a general purpose primer.

Preparing Bare and new wood for painting

  • This must be primed, or the new paint will not take properly. If there is any roughness, sand it down first. It’s worth going over the whole surface using fine grade glasspaper.
  • If there are any knots in the wood, seal them with a couple of dabs of knotting compound.
  • Once the knotting is dry, apply the primer. Aim for a thin, even coat. If you are just priming bare patches on an otherwise painted surface, stop at the edge of the bare wood —don’t try to carry the primer over onto the painted area. On moulded surfaces, take care that you coat all parts thoroughly.
  • Allow the primer to dry completely. Primer has a way of revealing scratches and blemishes which are barely visible on an un-painted surface. If you want a really profes-sional finish, it’s worth dealing with these now — but it’s not essential. Fill them with a fine surface filler, smoothing it down as well as you can and then sanding lightly once the filler has dried hard.
  • Apply an undercoat to the primed areas before topcoating.

When the surface is prepared, you must make sure that the room is clean and dry, and that there is no dust in the atmosphere to contaminate the new paint. Start by removing the dust sheets and getting rid of all the dust and shreds of old paint clinging to them. Then vacuum clean the room of any remaining dust and wipe down the surfaces before relaying the dust sheets.

  • Keep further dust down by limiting the opening of doors and windows as much as possible — but do bear in mind that some ventilation is essential.
  • As a final measure immediately before you start painting, wipe the surface over with a soft cloth moistened in white spirit. Then, as soon as it dries, apply the paint.

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