General FAQs

General FAQs


How can I quickly test for rotten wood?

  • Simply run a pen knife blade across the grain. This will only make a small indentation on sound timber, but on rotten timber the blade will sink in. The only cure is to cut out all the rotten wood and replace with sound timber.

What causes adhesion failure on metal?

  • Adhesion failure on metal substrates, resulting in blistering, flaking/delamination and corrosion, is usually due either to surface contamination or poor surface preparation.

    Among the most common types of surface contamination are grease on new galvanised surfaces and wax residue resulting from the use of chemical paint strippers, which should be cleaned with an emulsifying Oil and Grease Remover. Dust and general debris should always be vacuumed away before painting.

    In terms of surface preparation, the failure to remove millscale from hot rolled mild steel prior to painting can lead to serious problems months or even years later. Similarly, painting over rust can result in the paint film flaking or the rust breaking through the paint film.


How can I avoid stains or discolorations bleeding through paint surfaces?

  • Common causes of bleeding from the surface below include old wallcoverings, bituminous paint and creosoted surfaces, so these should be completely removed before painting. If this is not possible apply one or, in severe cases, two coats of Dulux Trade Aluminium Wood Primer. This link goes to an external site. New creosote or bituminous materials must be aged for at least 12 months before painting. For staining by metallic inks in wallcoverings or felt tip pens, the surface should be touched in locally with Dulux Trade Alkali Resisting Primer. This link goes to an external site.

Why does paint stain and discolour on masonry?

There are a number of principal causes:

  • Certain types of sand used in the construction or rendering of a building can cause staining, as can certain kinds of brick hollow clay pots or clinker blocks containing soluble salts. Pieces of ferrous metal or iron stone embedded in the material can rust and discolour when the surface is painted. These problems can be treated by sealing the affected areas with Dulux Trade Alkali Resisting Primer. This link goes to an external site when the surface is completely dry.
  • Rust staining can occur where old nails are left in the substrate, or a wire brush has been used to prepare the surface. In this case, prime locally with Dulux Trade Metal Primer. This link goes to an external site prior to painting.
  • Steel reinforcing in concrete may be too close to the surface and cause rusting. The only effective way to resolve this problem is to get back to the metal itself and treat the cause of the rust. Before repairing the surface and repainting.

  • Mould flourishes in conditions of high humidity, poor ventilation and on surfaces with a high moisture content. Condensation or poor air circulation is normally the main culprit. It can be very destructive to paint coatings and needs to be eradicated before applying paint. Treat affected areas with Dulux Trade Weathershield Multi-Surface Fungicidal Wash. This link goes to an external site. Leave for 24 hours, wash down to remove residues and allow to dry thoroughly. If necessary, repeat the treatment. Improving the ventilation and the use of mould inhibiting paints such as mouldshield will reduce further contamination.

How should I deal with old painted surfaces?

  • The British Coatings Federation website provides useful guidance on repainting and removal for professional painters and decorators, including a downloadable brochure.

  • Dulux Diamond Glaze will do the job. It will not yellow with age because it is water-based. It is also up to 10 times tougher than conventional varnishes. Apply one coat of Diamond Glaze Clear Gloss to seal the floor and then, rubbing lightly in between coats, apply two coats of Diamond Glaze Clear Satin.


  • Surfaces where the colour has faded due to exposure to ultra violet sunlight should be thoroughly cleaned down to removed all dirt, grease and surface contaminants. Then rub down with a suitable abrasive, dust off and paint over.

    Weathered woodwork previously coated with a woodstain or varnish should be thoroughly prepared to remove all grey denatured timber prior to redecoration.

How can I treat patches of uneven glossiness that appear when using non-glossy finishes?

  • This is known as "flashing". Paint flashing is the appearance of dull or shiny blotches on the painted surface. Paint flashing occurs due to a couple of main reasons: inadequate priming of surfaces that are porous and lack of correct painting techniques such as overlapping and not maintaining a good wet edge.

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