Tuesday, October 09, 2007

Lead paint

Above:Door painted with lead based paint

Technical Advice taken from SPAB (Douglas Kent, the SPAB technical secretary)
What is Lead paint?
Lead paint comprises lead pigment, usually lead carbonate ("white lead"), bound in oil. The pigment creates either a white paint or a base for tinting with colour. Historically, linseed oil was the usual binder and turpentine the thinner, their proportions determine whether the finish was Matt or semi-gloss. From the 20Th century, the flow gloss and drying time was improved by using an alkyd resin medium and the addition of titanium dioxide pigment boosted the covering power.

Lead tetroxide ("red lead") has been used extensively fro metal primers. Mixed with lead carbonate, it forms a pink lead primer for joinery.

Where might lead paint be applied?
Lead paint was popular until the 1960's, particularly on timber and metalwork. It was also applied to lime plaster in grander buildings (this had to have carbonate paint is now restricted by law for use on listed buildings grades I and II only, or, in Scotland, grade A), scheduled ancient monuments and works of art. Where care is taken, its careful application is to be encouraged, especially for the protection of 18Th and 19Th century joinery and conservation of important historic interiors.

What are the pros and cons of lead paint?
Lead paint has unrivalled durability on timber, possessed good flex ability and is "breathable". Its texture, depth of colour and mellow appearance are difficult to emulate with alternatives, and it emits less environmentally harmful volatile organic compounds (VOCs) than modern oil paints.

The main drawback with lead paint is toxicity. A health risk only exists, though, where lead compounds are ingested or inhaled due to unsound or disturbed paint. Dust from sanding old lead paint is the greatest hazard. The presence of lead paint does not justify stripping historic joinery.

How do I identify lead paint?
Old lead paint frequently has a creamy or soft colour. Rather than splitting and peeling, it may develop a fine, oblong pattern of cracking. A chalky surface can provide a further clue, but is not exclusive to lead paint. Detached samples feel heavier than with other paints. Lead paint might be present in nearly any pre-1960s building. Its existence can be confirmed with a DIY test kit or more sophisticated analysis. Where found, it could be safer to renew or cover coat lead paint than attempt its removal. If removing, use wet (not dry) sanding, chemical strippers or low-level heat.

How do I obtain lead paint
Supplies of lead carbonate paint are limited, but still available. The SPAB may be able to advise. You must declare that your intent is lawful, using a form the supplier usually provides. Approval takes several weeks. It is not required when buying red lead paint.

On buildings where the use of lead carbonate paint is no longer permitted, a compatible alternative, such as linseed paint, may enable the retention and over coating of old lead-based layers.

How do I apply and renew lead paint
External redecoration on a 5-10 year cycle is not untypical with lead paint and, internally, it needs renewing infrequently. Because it tends to erode rather than peel, surface preparation may require little more than washing with sugar soap and, where necessary, lightly rubbing down with wet abrasive paper. Only loose paint needs scrapping off. When taking back non-lead overcoats, remove all stripper residue thoroughly. Vacuum cleaners must have HEPA filters. Children and pregnant women should not be present.
Lead paint should be well-stirred and applied thinly with good bristle brushes. Each coat must dry properly before the next is put on. Natural oil based formulations are slow drying and demand great skill by the painter.

Note: I strongly disagree with the idea of using lead-based paints - TK

[Cornerstone Vol 28, No 3 2007 www.spab.org.uk]

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