Primers are used on bare surfaces (e.g. wood and metal) and are usually white or off-white, sealers are used on plaster or masonry and are normally clear or only lightly pigmented, and undercoats (sometimes called mid-coats) are used onto coated (primed or painted) surfaces and are always pigmented. For exterior masonry, surfaces can variously have a high pH level (alkaline), be chalky/powdery, or staining, which can cause adhesion problems and discolouration of the finish. While in most cases, if the surface is sound and dry, there is no need for a primer, but when you need one – use one. A specific masonry primer such as Dulux Trade Alkali Resisting Primer will allow you to safely paint over a wider range of pH levels without risk of adhesion loss, and we would recommend Dulux Trade Weathershield Stabilising Primerto prime/seal unstable areas. Priming FAQs

This can cause a headache for both walls and woodwork. If the previous colour was dark, this has can ‘grin’ through the new pale finish, meaning you may need an extra coat or two. This can be avoided by obliterating the dark shade using an undercoat on woodwork and a coat of a pale Matt wall paint on the walls. Of course, this also works if you are painting over a pale shard with a dark one, you just use a dark undercoat/matt instead. Bare plaster that is fully dry may be “primed” with a thinned first coat of Vinyl matt(“Mist coat”). Filled sections should be dealt with in the same way (i.e. patch-primed). Bare plasterboard should be primed with Dulux Trade Drywall Primer Sealer. Painting Bare Wood Note: You may also be confused by the various terms used, and what the difference is between primer a sealer and an undercoat. While some manufacturers add to the confusion, it may be worth offering a general explanation. Should I prime metal?" - Untreated metal requires a primer to seal it from exposure before any other paint may be applied. In certain circumstances, specialist primers will be required, for general metal work we recommend Dulux Trade All Purpose PrimerYou will know its mostly good practice to prime any baresurface before applying paint, but you’re probably confused by the number of primers on the market, and what should be used where? The terms often get mixed up and depending on where you are in the UK, you might use alternative terms. Just to confuse matters further, we also have primer/undercoats and primer/sealers, which do both jobs! Surfaces that are already painted and in good condition can simply be over coated (after cleaning and a light sand). Always use matt paint as an “undercoat” if there is a dramatic colour change, even if you are finishing with soft sheen or silk.

We have outlined the major benefits of priming (or undercoating), and when (and where) you may need to use a specific product. We’ve also given you a link to some of our tried and trusted “priming” products to help you make the right choice, and you can find our full range of “primers” here. When do I need a “primer” for internal walls/ceilings?The easy answer would be “always”, particularly on bare surfaces, but of course it’s not that simple. The main benefit of a primer is to even out the porosity of the surface and ensure optimum adhesion so that you get the best possible results from your paint system, but other features might include stabilising a powdery surface or helping to prevent stains ruining your decoration. Bare plaster that is drying out should be coated with a breathable finish such as Dulux Trade Supermatt.