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Here's an interesting question I heard the other day. If you look at old unpainted corro iron roofs pre 1960's I think, you will frequently see sheets alternating between rusty and not(so rusty), ie one is rusty, the next less so, the next rusty, the next less so... etc. Why do you think that is (I know the answer BTW)?
If you know too, don't post the answer straight away:wink:
Cheers
Michael
it only rains on every 2nd sheet
good pick up
i want to see the end of this
glen
I know because I used to work for Lysaght/BHP but I wont tell but if you do a search i'm sure I am have posted the answer here before.
Unders and OversQuote:
Originally Posted by mic-d
as in the lap
I dont know so i will have a guess - if its right i'm sorry for spoiling others attempts.
How did i go? yep got it right so i deleted it for others to guess
Cheers
In other words .....Quote:
Originally Posted by Calm
Unders and Overs
as in the lap
I seem to remember something about an oil coating sprayed on one side , to stop the sheets sticking together .
But I could be wrong eh :U
That's one of two reasons covered
What's the other reason David?
Bob that was a guess - got no idea and i deleted mine so others can guessQuote:
Originally Posted by echnidna
Cheers
Reason for the alternating under sheets and over sheets , was so that the whole iron roof did not peel off in high winds .Quote:
Originally Posted by echnidna
You better post the definitive answer Bazza, just in case I'm wrong:wink::)Quote:
Originally Posted by Barry_White
Cheers
Michael
Well that's not really the reason for overs and unders. When corrugated roofing was first manufactured it was made on a barrel corrugator (see picture) and the maximum sheet length was 3.000m or 3.600m.That is why all the old roofs on long runs had sheets end lapped. When the sheets were put through the corrugator the sheets had a overlap or an underlap on both sides depending on which way the sheets were laid.Quote:
Originally Posted by Manuka Jock
Attachment 104809
The under sheet was always laid with laps turned up and then the next sheet was laid on top with the laps turned down. Hence the term overs and unders.
All corrugated roofing is now made on a rollformer (See Picture) and with sheets when they come out of the rollformer one side of the sheet has an upturn and the other side has a downturn which always goes on the top of the upturn so you can then start at one end of the roof and keep laying the next sheet on the top of the previous laid sheet.
Attachment 104810
As far as the wind is concerned you always lay the sheets away from the prevailing winds and if a roof is properly laid with the correct number and type of screws it is unlikely a roof would blow off anyway. In cyclone areas all roofs should be fixed with cyclone assemblys.
Interesting info and photos Barry , not overly relevant to the question.Quote:
Originally Posted by Barry_White
So how many roofs , in New Zealand , were screwed down , rather than nailed down , before 1960 ? :rolleyes:
And when did cyclone assemblies first get used in New Zealand ? :U
Note that the opening question refers to "old unpainted corro iron roofs pre 1960's"
And does not specify any particular place on earth.
cheers,
Jock
This is my take on it but as I think Calm said it was in the process of dipping the sheets in the galvanising one side of the sheet received a heavier coating of gal than the other.Quote:
Originally Posted by mic-d
With the process of galvanising the heavier the coat of gal there is a direct relation to the time that the gal sacrifices itself to protect the black streel.
With Zincalume coating the relationship of time to the deterioration of the coating is enhanced by up to eight times. So with gal lasting up to 80 to 90 years zincalume could last up to 700 to 800 years.
As I heard it and it fits with what's been written. The older corro was 9 corrugations wide, that is, ends with 2 upturns or 2 down turns, to get the correct overlap, adjacent sheets were laid 'flipped'. Because the sheets have two different faces, they will experience slightly different environments in the manufacture or handling process if those processes require a particular orientation of the sheet to feed through machinery etc. Manufacturing tolerances mean that one side may get less gal, or some property that makes it rust faster. Modern sheets are 11 1/2 corrugations wide so could be laid either face up, they might therefore rust randomly or not at all for 700-800 years:oo:
Is that true Barry? Is Zinc better than the old gal?
CHeers
Michael
Can't really tell you much about NZ Jock but I know they where still using nails here in OZ up until Cyclone Tracey in Darwin, (that really changed the paradigm) they were also using old round head wood screws with lead washers (don't know when that started). Self Drilling and Type 17 screws didn't get invented until about the early 70's.Quote:
Originally Posted by Manuka Jock
Don't know about cyclone assemblies in NZ either. Is NZ really in the cyclone belt.
Here is a picture of the various regions in OZ.
:D:brava:clap::woot::hpydans2::hpydans2::hpydans::omg::welldone::cheers2: :I'mright:
What a guess and it was right. - check out my profile page to get address for the award/present/money/cheque/whatever i get.
Cheers
MichaelQuote:
Originally Posted by mic-d
Not sure on the no of corrugations on the old corro but the current one is 10 1/2 corrugations and they make an eight corrugation sheet for tank makers.
Actually the term galvanizing is the process but it is done with pure Zinc. Zincalume is actually a combination of Zinc and Aluminium . When they first brought Zincalume out they said it would last four times as long as gal but they were then saying in areas inland would double that.
Interestingly they will only give you a maximum of 25 year warranty to perforation and that comes with quite a few strings attached to it.
All other comments I would have to agree to.
Calm
BTW you should read the heading for the Quiz Forum and the prize is the glory of answering and participating
Bazza , we get about one cyclone a year , generally up north .
Can't remember exactly when we started using self drillers mid 70s maybe ,
and type 17s , dunno , but battery drills have spread them around .
With the advent of roofing specialists , we chippies don't do a lot of it these days ,
thankfully , hauling longrun is not my cuppa tea anymore .
Now I'm not sure either, I counted nine on the old stuff, but if I couldn't count the new one to 10 1/2 then who knows?:doh:Quote:
Originally Posted by Barry_White
Cheers
Michael