Surface defects

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Painting and Decorating NVQ and Technical Certificate Level 2, 2nd Edition

You can clean off rust by hand, using a wire brush, paint scraper, chipping hammer or abrasives – or a combination of all of these!• Remove traces of oil and grease.• Scrape off all loose rust.• Use a chipping hammer around rusted

nails, etc.• Use a wire brush, but avoid burnishing.• Finish off with a rough aluminium oxide

abrasive.What is burnishing?

Corrosion or rust: removing by hand



It is quicker and more effective to use power tools to remove rust – but take care not to over-polish the surface.• Remove traces of oil and grease.• Scrape off all loose rust.• Use a needle gun to remove rust

around corroded nuts, etc.• Select appropriate method:

sander, rotary wire brush, angle grinder.

Why is over-polishing a problem?

Corrosion or rust: removing with power tools



Paint can be removed in a number of ways:• with an LPG burning off torch• with a hot air stripper• with chemical paint remover.

What are the advantages and disadvantages of each method?

Painted surfaces in poor condition



Abrading surfacesAbrading means wearing away the top layer by rubbing. This provides a key for the coating or covering to be applied to, and gives a good quality finish. Abrasive materials need to be:• not too rough – this can leave scratches• not too fine – this may be ineffective• of good quality – cheap ones don’t work

well!

What are wet and dry abrasives? What are dry abrasives?



Mechanical sanders can be quicker and more effective than manual sanding techniques, but may only be suitable for certain areas – and can create a lot of dust.

When is it best to use a heavy duty sander, and when a rotary sander?

Mechanical sanding



A friable surface is one that crumbles away easily when you rub your hand over it, such as weathered brickwork. If paint is applied to a friable surface, it won’t last very long as it will come off as the surface crumbles.

How should you treat a friable surface before painting it?

Friable surfaces



To remove mould growth:• Wet the mould.• Remove heavy patches with a

scraper or brush.• Apply a fungicidal wash.• Leave for a week and re-treat

if necessary.

Why do you need to wet the mould before removing it?

Mould



Defective puttyIf you notice a gap between the old putty and the glass, you must seal it completely by forcing in linseed oil putty using a putty knife.

What should you do if any bare timber is exposed?



Apply a hard waterproof coating to plasterboard before applying surface coverings like wallpaper. This will stop the covering bonding with the surface, and prevent damage if the wallpaper is removed later.

How is plasterboard constructed?

Damage to plasterboard



Moisture penetrates cement, dissolving some of the lime, creating calcium hydroxide which rises to the surface as a white patch. Remove any efflorescence with a stiff fibre brush or wire brush before decorating.

Why should you not try to wash off efflorescence?

Efflorescence



• Rake out any loose coatings and rendering.• Undercut the crack.• Point up the crack with mortar.

What tools are needed to repair this defect?

Repairing damaged rendering



Caulk is a waterproof filler and sealant, used in cracks and gaps. Mastic is one sort of caulk. To apply caulk correctly:• apply the caulk, usually with a gun• wipe across the bead with a wet finger• remove any surplus with a filling knife• sponge off any remaining material.

Why is one of the applications on the right incorrect?

Caulking

Surface defects

Education

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