We have been living in our BISF house for over a year now and have already knocked through kitchen/dining room to make a kitchen diner, added a new bathroom upstairs and have also knocked down the outhouse and rebuilt turning it into a utility room and clockroom.
We will probably do the hallway next taking down all plasterboard, replacing and re decorating.
Anyway my question is regards to decorating the outside - we are looking to repaint the top half of the house and im wondering how this can be done? do we have to remove all the old paint or can we paint straight over it?
Hi Marissa, it’s good to hear that your project is coming along and I must say that the new utility room looks great from what I can see.
As for painting the external steel cladding, it may surprise you that this is one of the most difficult questions to answer as we are never able to determine the exact type(s) of paint the have been applied and built up, layer by layer over the years due to repainting.
I have seen many cases where Councils (typically) have overpainted the steel cladding using a type of paint that has reacted with the underlying layer causing severe blistering, peeling and cracking and of the new paint layer. Unfortunately, we do not know what type of paint these Councils' used or the composition of the old paint onto which the new covering was applied. We also don't know if the old surface was cleaned correctly or keyed prior to application which can also result in peeling.
Therefore, it is quite possible that peeling was due to either, (a) chemical reaction between the old and new paints. (b) Insufficient surface preparation (such as sanding & cleaning to provide a good key) or (c) Unsuitable choice of paint that is not suitable for application onto a steel/metal surface due to extreme temperature variations causing expansion and contraction which the paint cannot handle.
Whilst trawling through my original 1940's British Iron & Steel Federation research documents, I have found conflicting references as to the nature of the original paint which was applied during construction. One document, which can be seen below, specifies an oil-based paint, whilst another, which I have not yet managed to dig out, referenced exterior masonry paint.
Today, oil-based paints are not recommended for use on metal or galvanised metal surfaces. Fortunately paint technology has advanced much since 1946 and we now have a variety of newer paints that appear much better suited to this type of surface. One such paint is DTM or Direct To Metal paint. This paint has been specially formulated to deal with the expansion and contraction of metal surfaces due to heat fluctuations. Many contain latex, which itself is flexible helping the top coat last longer, whilst reducing the likelihood of failure.
I personally would not remove the existing paint if the current surface appears sound and well bonded as the task itself would require an immense amount of hard work without a guaranteed result. You could also possibly expose and damage the galvanised coating. Exposed galvanised steel can also oxidise and prevent new paint from adhering effectively unless it is repainted soon after exposure.
In basic terms, it is not dissimilar to repainting a huge galvanised steel garage door and if certain steps are followed, you should be able to attain good results providing there is no reaction with the underlying coat. Paint reactions generally occur when the coat contains epoxy, polyurethane, or similar type of chemically cured coating.
Finally, if you do see any areas of exposed galvanised metal, this should be treated carefully before new paint is applied. I've managed to find a link that might help explain this better HERE
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