PREPARING SURFACE (Part 3)

Preparing Wood and Metal

In your residential or commercial painting project, whether your woodwork or metalwork is brand new or old and coated with layers of paint, it will need some surface preparation before you paint. Adding another layer of paint to a door, window frame or metal balustrade will seldom hide imperfections in the layer beneath.

WOODWORK
      New bare wood

• Apply wood primer – two coats to knots to stop resin bleeding from them.
•  look for cracks and blemishes which need filling. Use fine surface filler for interior wood.
• Smooth the wood by hand, using fine abrasive paper, working with the grain. Alternatively, use an orbital or multi-purpose power sander, again working with the grain. Be gentle, because with power tools even the tiner grades of abrasive paper can remove wood very rapidly.

        Old bare wood

•  If there are signs of wet rot – soft patches easily penetrated by a penknife blade – then these will need to be dealt with.
• Fill all cracks and gaps with filler as for new wood. When set, smooth with fine abrasive paper.
•  As soon as preparatory work is complete, apply a coat of wood primer.

       Painted wood

• If paint is sound and in good condition, do not strip it unless the thickness causes an obstruction – making windows hard to open, for instance. Instead, clean with sugar soap and water. This removes dirt and keys the existing paint so that new paint will adhere to it.
• Keying (roughening a gloss surface very finelyl is essential; without it new paint is easily damaged and scratched off.
• Where paintwork is slightly damaged but mainly sound, only work on the damaged areas. Rub with a damp, flexible sanding pad to remove all loose material, wipe clean and allow to dry, Prime bare wood where it is exposed. Then lightly rub the whole area with very fine abrasive paper and wash with sugar soap, as for sound paintwork, Fill small chips with fine surface Filler.
  Lacquered wood
•  Use a chemical paint stripper to get the surface back to bare wood.
  Stained wood.
•  If the wood is to be painted and the stain is old, rub down with a foam-backed flexible sanding pad. If the wood is to be sealed to give it a natural finish, remove the stain with a wood bleach. Follow the instructions on the container. Dark colours can be hard to remove.
  Wood treated with preservative.
• Coat the wood with an oil-based primer. Otherwise the preservative may bleed through any new paint.

METAL
         New iron and steel

• Degrease with mineral turpentine, then use abrasive paper to remove rust and wipe clean. Finally, apply melal primer.
  Old rusted iron and steel
•  Wear safety goggles and leather or rubber gloves for protection.
• Use a wire brush – either hand or mechanically driven – to remove all rust.
•  Treat the affected area with a rust converter, following the manufacturer’s instructions carefully.
• Prime the surface with a metal primer.
•  Fill any defects or holes with a two-pack epoxy filler and allow it to set.
•  Apply an oil-based undercoat, followed by the finish of your choice.
  Mill finished (uncoated) aluminium
• Degrease the surface with mineral turpentine.
• Apply a coat of etch primer — a chemical that bites into the surface, creating a key for future coats of paint.
• Finally apply the finish of your choice.
  Anodised aluminum (such as that used for making windows and patio doors)
• Degrease the surface with mineral turpentine.
•  Sand back with 180-grit aluminium oxide paper.
• Apply a two-pack epoxy primer, followed by an acrylic or enamel finish.
  Copper (such as central heating pipes)
•  Remove any protective grease with mineral turpentine and rub away any discolouration with fine abrasive paper or wire wool. Wipe clean, then apply an etch primer and a layer of oil-based paint.
  Stainless and chromium-plated steel
• Treat this material in the same way as anodised aluminium, see previous,
  Painted metal window frames
• As with painted woodwork in good condition, do not interfere with sound paint on metal, unless a build-up of paint is making frames too tight, causing them to bind.
•  If the paint does not need stripping, clean down the frames with sugar soap and water. Key the surface by rubbing with fine abrasive paper or wire wool, then apply a primer, followed by gloss paint.
  Where rust is lifting paint
• This may be found in older houses where metalwork was not galvanised.
• Wear safety goggles to protect your eyes and brush away flaking paint with a wire brush. Scrape back the remaining paint lo reveal bright metal. Do not ignore any hidden rust; it can lead to a new attack. See the treatment recommended for old rusted iron and steel (left).

   Tip
      FOR A PERFECT FINISH
To avoid a disappointing final appearance, sand wood smooth and fill any holes before painting.

• Wrap a piece of abrasive paper around a wood sanding block and rub it along the grain of the wood.
• After sanding, use a fine brush to remove all the dust, brushing in the direction of the grain to clear all crevices.
•  Press the filler into the holes, taking care not to spread it into the surrounding grain.
• Wait until the filler has dried to the same colour all over – perhaps 15-30 minutes – then sand it flat and dust once more.