Mill Scale

[Breals]

Hi all.

 

After cruising my freshly blacked narrowboat home last year, the numerous collisions with lock entrances, banks, bridge holes etc (I am much better at handling the boat now, BTW!) had knocked off patches of blacking revealing smooth orange coloured metal underneath. After reading these forums I think this is mill scale. More blacking has been knocked off since and I am sure that the problem lies with a lack of adhesion of the blacking.

 

I would like to dry dock and patch up the blacking (especially at the waterline where there is rust rather than mill scale) but would it be better to treat the mill scale first - and how would this best be achieved?

[John Orentas]

Hi Breals.

 

That orange coloured stuff is rust which forms on the steel after you have knocked the mill scale off. A few patches of rust at the waterline can simply be painted over, can you move some heavy items around inside the boat or use the centre line to put a list on the boat while you do the job.

 

When the steel is new the mill scale is only a few thousands of an inch thick, very hard and very difficult to remove, even grit blasting struggles to shift it, when the boat is 5 years or so old the scale increases in thickness to 3mm or more and has softened to the point where it can be fairly easily removed.

[Breals]

Thanks John. Will have a go at getting the waterline repainted as you suggest. The other bare patches where the black has 'dropped off' are easily repainted, and anyway seem very stable smooth and shiny, so I'm not too worried about these - its just cosmetic.

Edited April 28, 2006 by Breals

[Maffi]

Thanks John. Will have a go at getting the waterline repainted as you suggest. The other bare patches where the black has 'dropped off' are easily repainted, and anyway seem very stable smooth and shiny, so I'm not too worried about these - its just cosmetic.

 

 

Might not help your situation but interesting nonetheless.

 

http://www.hamiltonform.com/faqs_mill_scale.html