Christmas and New year seem a while back now. Although very welcome, the holiday break disrupted our schedule again (if you’ve read the previous Blogs you’ll know we started a week late due to site preparation problems). With that said, we managed to get a couple of weeks of recording work in before Christmas just as we got going we had to stop.
Back to work again and it took a few days to get back into the swing of it. We had a good week 3, and made a start on phase 3 of the project which is to clean and consolidate the Ironwork structure. This work involves cleaning back whats left of the painted surface of the Ironwork, removing built up corrosion as we go. We are trying to achieve a suitable surface to prime ready for new coats of paint. It is obvious to a practical person what this all about, but I’ll elaborate a bit.
Our primary job in this phase is to conserve the existing structure. Conserving Wrought Ironwork generally means tackling corrosion and the damage it can do, there are other things to consider but I don’t need to bring them up here. There is little point in painting over layers of paint that potentially mask the wrong sort of corrosion. ‘Wrong corrosion’ I hear you say! All metals oxidize a little during and after manufacture and quite a bit during working, you can endeavor to remove these oxides, but metals ‘prefer’ this state . If you observe stocks of Iron and Steel in dry store they are quite stable with this oxide layer in place. It is only when look carefully at the stock you see scratches and scrapes (due handling process) corrode in the known manner (that’s the wrong corrosion). So it goes to say the right metal oxidization goes someway to protecting the metal, and if possible should remain if found or be encouraged, through correct hot working.
So the paint has to go, and we need to get down to the metal or as near to it as we dare. The paint has been already tested and recorded by an independent specialist, so that doesn’t need recording unless something else turns up. The tenacious grey primer you see in the photos has been applied over a thin black coat of paint. Its interesting to note that both these paints have been applied in void areas caused by layers of corrosion to build up then fall off. This suggests the paint layers you see are unlikely to be original and must be maintenance measures taken after significant corrosion had already set in.
The procedure (we know it as ‘method’) for cleaning of this large structure is to pressure wash the algae, dirt and loose paint off, being mindful that general debris needs to be collected as best possible and disposed of responsibly, anything of interest recorded and reserved. Then the remaining surfaces have to be flame cleaned, loosening the remaining paint and rust that then can be scraped, chiseled or brushed.
Where the metal is corrosion free, as much original surface should be preserved by careful brushing only . If the cleaning is conducted with the correct method, the resultant surface should be rich in character and most importantly as clean as possible (free of all but the most persistent primer and rust). There is of course a practicality issue here, namely there is only so much one can do with brushes and scrapers. It is so important that a Conservation Blacksmith is mindful that a more aggressive approach will start to undo good conservation philosophy and could damage the original structure more than the natural processes you are trying to halt or retard. This is why you don’t chemically strip the metalwork of all oxide, apply rust converters, shot blast or use a needle scaler.
Priming the cleaned surface as soon as possible is important, there is little sense in doing all that tedious work only to waste it by allowing the corrosion process to get a fresh hold.
This painting can be applied as a light holding primer, this is the perfect start for the whole project. For the record, and with 20 + years of experience, cheap paint isn’t good value. Buy the best, it pays for itself in the long run.