Simulating iron roofing

[mattog]

What humbrol colours/blends would one use to simulate corrugated iron roofing, fences etc? Any links to any 'how to' pages would also be appreciated.

[RBE]

It really depends on whether you want it reasonably new or rusted to hell derelict. The material itself is galvanised steel (sometime asbestos though which is a different animal) so is a kind of mottled silver when new, this flattens as it weathers. So a base coat of silver (possible finely stippled with gunmetal or an humbrol metalcoat if you really want to play, don't do big blotches though or it will look a mess), this then needs a coat of matt varnish to kill the shine. After that it really depends on what your after really. The grooves tend to catch dirt and rain on roofs which then promotes growth of mosses and algae. General airborne dust and dirt land on there too, any ventilation or extracts tend to deposit darker dirt and grime plus the odd run or too where any expelled vapours condense outside. Deep scratches which go through to the steel below the zinc coating will rust so that is something that you can add too but think about where this is likely to happen, on roofs its more likely where people may be working or accessing. Fencing is more likely to be knocked and thus rusting more common than on a roof. As for colours, natural browns and greens for the dirt and mosses, something for texture is nice (fine flock added to paint can give a good moss effect) For industrial dirt you might want some various shades of grey. I tend to mix and match my colours as I go, looking at pictures of something like I'm trying to acheive. Its all brushwork really so I generally do a little pallet like an artist would use and mix em around a bit. Acrylic dries incredibly fast though so watch out for that. If you are using enamels then its not quite so bad. However, I do feel that for scenics, acrylic does come into its own!

 

Cheers

Cav

[Shamouti Ben Yafo]

Deep scratches which go through to the steel below the zinc coating will rust...

 

This is known as Galvanic corrosion - this happens whenever dissimilar metals are in contact in a hostile environment, like - oh, let's say - steel and zinc! One scratch and rust does indeed set in, so rusty panels need not be that old. An excuse to get artistic with fresh yellow streaks and older red-brown.

I (and, I'm sure, plenty of others) have always regarded Zinc plating as protection in storage rather than use, so why not mix some matt black and chocolate brown so you can slap on the good old (simulated) bituminous paint?

[big_daddy_ray]

may I just say that both those replies are very helpful and I will be experimenting with both

[Chinahand]

Have you thought of just covering whatever it is you're modelling, with a texture sheet. It saves the hassle of painting something like this.

 

CG Textures have some good examples of corrugated iron in various stages of disrepair. CG Textures

 

At the very least they could give you a guide to colurs etc.

[RBE]

This is known as Galvanic corrosion - this happens whenever dissimilar metals are in contact in a hostile environment, like - oh, let's say - steel and zinc! One scratch and rust does indeed set in, so rusty panels need not be that old. An excuse to get artistic with fresh yellow streaks and older red-brown.

I (and, I'm sure, plenty of others) have always regarded Zinc plating as protection in storage rather than use, so why not mix some matt black and chocolate brown so you can slap on the good old (simulated) bituminous paint?

 

Hmm kinda, in fact the galvanising is there to stop the corrosion and does so remarkably well. The zinc coating is a lot more reactive to oxygen than the steel so therefore corrodes to zinc oxide rather than the steel to ferrous oxide or rust as it is better known. The zinc is whats called a sacrificial annode and during the reaction of the steel with oxygen instead of producing iron oxide the zinc gives the steel (or more accurately the iron in the steel) an electron thus opening a valency in the zinc for the oxygen to combine with. This actually creates an electrical current between the two which is cool but no relavance here. Of course though a big enough scrape right into the core of the steel and you do run the risk of rust. However galvanising is far from being the protection in storage talked about above, its actually a fundamental defence against corrosion without which all of todays metal structures could not exist. In fact there are marine applications where simply bolting a large lump of zinc to a steel structure stops corrosion using the sacrificial annode principle alone. Normal galvanising tends to break down when enough of the zinc has reacted so that sacrificial properties no longer benefit (takes a long long time though) and the oxide surface is scratched. The paint referred to in the attached quote is actually what is used if the steelwork is to be internal and there are cost incentives involved. It is no where near as good at preventing corrosion and is almost always avoided externally! I have had two careers, the first as a material development engineer and the second as a designer in construction both of which have featured galvanising heavily. I'm not a smarty pants naturally!!

 

Cheers

Cav

[Shamouti Ben Yafo]

Quite - I am aware of the electrochemistry. It works well enough until it doesn't, then it's time to watch your fence panels rot almost before your very eyes. This is why everyone I've ever known who has used this stuff for fencing or any other application where the panels are vulnerable to damage gets out the brush. Not rebuilding your fence is indeed a cost incentive!

 

I'm not a smarty pants naturally either; I also had to work at it.

[mattog]

Thanks for the response. I don't have a Humbrol silver as I was of the opinion that it was a little bright for 00 scale and was favouring more of a matt grey. But I guess the Dull-Cote would knock it back a bit. My intention is to create a base coat of galvanised steel, seal it with Dull-Cote, then add a layer of hairspray then paint and once dry flake away the paint with a stiff wet brush. Rust spots would then be picked out with a fine brush. It's a method popular with military hobbyists and one I've used before for paint flaking off wood and rusting water cranes etc.

[DLT]

What humbrol colours/blends would one use to simulate corrugated iron roofing, fences etc? Any links to any 'how to' pages would also be appreciated.

 

Have you got the current (February) edition of Railway Modeller? I have an article in there describing my building techniques, including corrugated iron.

 

Good luck, CI is great stuff for modelling.

 

Cheers,

Dave.

[RBE]

Quite - I am aware of the electrochemistry. It works well enough until it doesn't, then it's time to watch your fence panels rot almost before your very eyes. This is why everyone I've ever known who has used this stuff for fencing or any other application where the panels are vulnerable to damage gets out the brush. Not rebuilding your fence is indeed a cost incentive!

 

I'm not a smarty pants naturally either; I also had to work at it.

 

You may be aware of the electrochemistry Shamouti, however you misquoted the galavanic corrosion, citing it as the reason why galvanised steel corrodes which is in fact the complete opposite. The galvanic corrosion between zinc and steel is what causes the zinc to be sacrificed in favour of maintaining the steel, this is one of the main reasons for galvanising as well as providing a thin coat of zinc-oxide which prevents oxigen reaching the steel below (while ever there is no freshly exposed steel of course due to damage). Galvanised corrugated sheet is pretty low tech though, being very thin and mass produced meaning that most people when installing cut and drill it all they like, and it does rust after a while especially where it's been cut and drilled and heavily dented bad enough to cause cracks in the zinc coating (which I believe I said previously when offering weathering advice). Galvanic corrosion is a major problem in architectual systems though where galvanised steel and aluminium are required in close proximity, however PVC tape between componants and the use of stainless steel fixings prevent this.

 

I didn't actually notice your bitumen paint quote before, I assumed you were talking about a coat in either red oxide primer or Galvafroid zinc rich primer, both of which aid the anticorrosion in the same way that galvanising does, only not as effectively as a paint can never hope to have the same level of bond with the substrate as galvanising. Bitumen sealing paint is used where a water seal is required, usually on concrete roofs and slabs, not generally over visual steelwork as protection, it is incredible messy even when dry and goes on really thick if to be effective in doing what your trying to do, create a water seal. Also repaints in something else is then prevented as you can't successfuly paint over it (to look good) either unless its with another thick unsightly coat of bitumen. I wouldn't want a metal fence painted in that, one around a scrap yard maybe where it doesn't really matter. A nice primer coat of the fore mentioned anti-oxidising paint followed by a top colour would look much better.B)

 

The cost incentives I was talking about relate to structural steel really not corrugated steel sheets (not iron these days, of course in the old days it was rought iron and suffered riduculously with corrosion) which in order to meet safety legislation must be corrosion protected (you missed the point really as in fencing you have no option but to buy the sheets galvanised). Galavanisation is the recommended method for any structural steelwork, however when costs are tight (galvanising isn't cheap) then as a second choice galvafroid or red oxide primer is acceptable if the steel is to be internal and not coming into contact with moisture or other harsh environments. Marine applications really must be galvanised as the salt in the sea water aids the oxidisation process and thus increases the waters ability to corrode. To say galvanisation is only really a coating to protect in storage is utter rubbish and as I've stated is required by law on exposed structural steel. To even imagine that a coat of paint is better beggars belief . Theres nothing to stop the paint being scratched in exactly the same way as the zinc coating except that the zinc coating is molecularly bonded into the surface of the steel by the process not just stuck over the surface like paint so is much harder to break through, it certainly won't chip or flake. Add to that the sacrificial nature of the zinc using its galvanic corrosion to help keep the oxygen from reacting with the steel and you can see its more then a storage packaging! You seem to forget that all corrugated steel is galvanised even the stuff you have painted over, its belt and bracers but granted worthwhile for low tech fencing panels where any number of things can break the surface, you need to repair the coating if this happens and painting with something is the only way really. Just imagine what it would be like if it weren't galvanised though, it would be rusty before it even left the production line in the factory. Rust on bare metal forms incredibly quickly.

 

Another rust which forms in these situations is white rust, actually its the zinc-oxide (or on aluminium as aluminium-oxide (alumina) which is also white so that may be added occasionally too) which is the corrosion thats formed instead of our usual orange ferrous-oxide. In weathering terms we can also add this. Anywhere that water runs and then dries, such as overflows or badly designed areas that may trap water can benefit from an application of dusty white. don't go wild though or else it will look like a china clay works!! Simple runs around drains and overflows or dusty patches where water might sit and evaporate will be enough. Add rusty rust as well around fixings and places where the sheets have been cut, these will be the araes attacked first. Look at photo's too this is the best way to get a feel for it. Now you will know what's happening in those pictures too!

 

All this isn't a poke at Shimouti by the way so please don't take it as such, I'm just providing info, I find this stuff very relevant to modelling and broadening the knowledge we have and seeing how nature does its thing helps us to make better models through our understanding. Science, art and weathering are a bit of a passion for me (unusual combo granted), weathering being one of the more artistic parts of modelling though I feel. It's one area where we can be more free with our expression.

Cheers

Cav

[Shamouti Ben Yafo]

Me too; having assisted numerous people in the past putting up such fences, I can testify that they survive the Welsh climate better with the tarry stuff - perhaps it also provided some protection from scratching. Nowadays everyone wants that ruddy useless larch lap stuff - I do wish my neighbour had asked before replacing my existing fence with that; it blows down every winter without fail.

 

As a Chemistry undergrad, I was taught that once sufficiently damaged this aforementioned corrosion sets in on zinc sheeting (colloquial term for galvanised iron in S Wales).

 

It's just dawned on me - you're a pukka engineer! Most people using this stuff weren't. For me the bituminous goo goes on! - But I model South Wales.

[RBE]

Yeah I kinda fell into the chemistry when I got into a career in materials science and engineering requiring me to do a 5 year degree course, I worked as that for about 12 years, now I design buildings which pays the bills a bit better. I have always preferred physics though, in fact I have an A level in astronomy which is quite random.

 

Anyway I digress, lap larch is the modern solution to fencing suppliers financial shortfalls! Whoever designed them ought to be shot. The windloading on those compared to strength is ridiculous, its inevitable that they are gonna come down!! Cha ching!

 

 

[corax67]

If you are looking at derelict/rusted you may like to look at this pic for inspiration (an old North Wales tin chapel)

 

http://farm3.static.flickr.com/2664/3743443566_1430850a9f_o.jpg

 

and for a really useful guide on how to weather then

 

http://www.scale-models.co.uk/content/weathering-8/

 

 

There also used to be a fantastic step-by-step article on the old On30 Conspiracy links page but I cannot remember what the layout/site was and the On30 Conspiracy site has vanished without trace. If I can find it then I will post it too.

[Shamouti Ben Yafo]

...lap larch is the modern solution to fencing suppliers financial shortfalls! Whoever designed them ought to be shot. The windloading on those compared to strength is ridiculous, its inevitable that they are gonna come down!! Cha ching!

 

Solution in the modern sense, clearly. I first saw this in the late 60s, I'm sure - it looked modern and stylish then, but in my defense I was only about 8 at the time.

 

As for shooting - let me reach for a bullet mould and bottle of phenolphthaline!

 

My own career in science sort of bombed out, and finding something I liked took a total of six establishments (four colleges, two universities) and a bunch of seemingly random qualifications. One of them is an honours degree.

 

Caution - as someone who knows well how things should be built (no, not me! Not even in my brief career in building...) don't be tempted to rectify matters in your chosen area - railway modelling is, apart from the actual moving parts, about how things were done. Sometimes historical accuracy is about bad science.