[Closed] Help me identify porch roof stain please.

Weird. Worth trying a bit of oxalic acid on it?

I say it's not rust as that was my initial feeling from the look of the cover and the intensity of the stain. Also you'd expect other areas to be affected in some way but everywhere else is fine .
I haven't been up to inspect but if it were tin coated perhaps water from the thatch may contain abrasive particles which have worn through the coating .. I don't know ..just a stab in the dark. It's the colour that's odd .

Assuming its metal and not fibreglass, he porch roof looks like lead to me due to the curves (zinc, aluminium or terne coated stainless steel tends to have far crisper edges).

I see similar stains caused by tannin leaching out of timberwork dropping onto lead, its possible that the thatch has a tannin content which is leaching out.  You also see similar stains when the iron content of certain types of stonework leaches over time.  In both cases the damage seems to be aesthetic rather than causing a problem with the lead.

Make a strong brew of tea and paint it over the whole porch roof. It won't get rid of it but it will look like it's supposed to be there.
I once had a large area of discoloured lead flashing that I wanted to tidy up. Everything you read about lead is that no paint will adhere to it. So while I decided what to do I painted it with some dark grey Dulux Weathershield undercoat that I was using on the adjacent woodwork. 10 years later that undercoat is still looking OK.

Richieb ... Funny .. I did think about tannins as he had an internal water leak a few year ago and the ceilings needed repainting . The water stains were a nightmare to cover even with numerous coats of zinnsers products.
I remember at the time talk about the area having water with high tanin content or something similar . Don't know if that makes sense.
So it may be lead .. mmm .. something told me not but you're probably right.

Well ..presuming it is lead perhaps a good clean , remove the stain by careful sanding ( facemask) wet paper. Then how about plenty of patination oil rubbed in ? Would that likely stop the stain coming back ...or should I try painting .. I know most paints don't do well on lead . Other suggestions welcome and thanks to all .

I remember at the time talk about the area having water with high tanin content or something similar . Don’t know if that makes sense.

Unless you live in a particularly interestingly polluted part of the world, tannin is usually something that water picks up by running over or through something rather than having when it falls out of the sky.  I’ve perhaps worked on two jobs in the last twenty years involving thatch so I don’t know a lot about how it decays over time but that would be my guess (or something similarly organic coming off it).

Thinking about it I have seen a couple of late nineteenth and early twentieth century porch roofs which were pre-fabricated by pressing so I wouldn’t completely rule that out although from the photo it looks more like something that has been formed in its current position rather than delivered.

If its not rust I am going with tannins too, we get this with new wood installations also.

Is it lead dioxide from the lime in the mortar? Doesn't it have to be treaed with an oil after fitting othrwise it oxidises firstly to lead oxide (white) then lead dioxide (reddish brown)? it might abrade away with wire wool.

Tanin s from the thatched roof

Some peeing out of the window every night ?

Is it a traditional thatched roof or has he got chicken wire over the top of the thatch to keep birds/squirrels out? could be rusty water from that dripping down.

Or possibly something leeching through from the underside? Wooden frame, cheap fixings?

Will report back after visiting on Friday . Wire wool may be an idea rather than sanding but he did that and it came back so trying to fix . I guess oil or suitable paint would stop any future discolouration if it is coming from above which my money is on. Too red for rust to my eyes . Lead dioxide ? Interesting but why not all over?
Thanks all... appreciate it.Bill

I also thought tannins.
When our {white} boat is on the sea for more than a couple of weeks. The hull gets a pale brown stain along the waterline from the tannins in the seawater.
I remove it in just a few seconds by wiping the hull down with oxalic acid - which is why I suggested it up there 👆

(It will also get rid of rust stains)

Not sure if use wire wool as it can break up and the individual wires will rust if left out.

Good points with the wire wool and oxalic acid .. I do actually have some in the garage .
Despite all the bickering and ego clashes on this forum it is a great source of knowledge from helpful people and has saved me a fair bit of time and money over the years.I have time but little money !
Cheers

it kinda looks like galvanised steel rusting

You could mix the OA with s bit of wallpaper paste to get it to stick to the slipping roof a bit longer than it would otherwise.

it kinda looks like galvanised steel rusting

It does a bit but the shape of the porch looks a bi to 'soft' a material to the steel. On galvanised stuff the zinc is a sort of sacrificial material - its not impervious to weathering it just weathers away much more slowly than the steel would - if theres a drip line from the thatch the zinc would eventually give up along that line. In which case the steel would be rot away pretty quickly there too - its not going to be a stain to be removed it would be the structural metal showing through

But if its lead or zinc and its just a stain then I think its actually quite nice - bit of patina - natural materials doing what they do.  If thats the case I suspect whatever you do to change it - time other than change the architecture,  the nature of the respective materials and the weather will change it all back again. So I'd leave it as is if it was my house.  Or maybe just replace it all with uPVC. 🙂

I would say tannins too ... but there's something odd about the pattern. Is the doorstep marked underneath where it drips over the top, too? You'd get that from wood tannins.
Why does it only extend so far to the right and left but not all the way to the edge of the roof?
I'd be tempted to pour some water off the thatch and see where it goes to determine if that's the source.

It does a bit but the shape of the porch looks a bi to ‘soft’ a material to the steel

These types of porches were mass produced in galvanised steel, I have not seen that exact shape but there is an street near us with pressed steel porch roofs made to look like lead.