Leak that is driving me crazy

Aluminium flashing into gal gutter and your gutter will be rusted out in short time by electrolysis so no go.

Two issues to fix:

1. Leaking gutter - So long as the gutter is cleaned according to instructions silicone sealants for gal should last 20-30 years. But this is probably best repaired using a full two-part waterproofing membrane system - talk to Bunnings. There are a number of product that will do the job.

2. Overflow - this can be fixed by effectively extending the gutter higher up the rafters on each side using ponding boards or sheets. These are lengths of galvanised flat iron bent to have a lip that sits down into the box gutter 30-50 mm and sit on the rafters under the tiles or sheeting - on top of battens usually.

They are pop riveted to the existing gutter, but if access is an issue can even just sit in place with silicon sealant liberally applied underneath to seal between the gutter and the back of the ponding sheet. If tiled roof then lift tiles and take the sheet say 300 mm up the rafters - a big increase in the holding capacity of the box gutter. If colourbond or similar roofing then simply undo the screws sufficiently to slide the ponding sheet up and under.

The other issue is the size of the outlet - it won't matter how big the box gutter is or is extended by ponding boards to be if the outlet is a 90 mm or 100 mm downpipe into a 100 mm storm water drain. So many houses have overflowing gutters because they have several downpipes (and/or a box gutter) all of which flow into a single 100 mm stormwater connection.

As others have said you need to enlarge the outlet at the end of the box gutter to the max and also have at least one overflow grate/ sump at ground level so that in downpours there is somewhere to ease the restriction of flow. And as was also said - check there are no blockages in the stormwater system.

One other thing - one fundamental bit or work that almost no-one does is to work out what carrying capacity the gutter and stormwater system as a whole needs to have.

To do this is simple enough - work out the surface area of the roof sections that will have rain flow into the gutter then visit the BOMS website http://www.bom.gov.au/hydro/has/FAQ.shtml and other parts of that site and look up the local rainfall history to find out the 15-year, 25-year 50-year and 100-year maximum rainfall events, work out the volume landing on each square metre and multiply by the surface area of your roof so you can then determine the maximum volume of water that has to get away down your gutters and drains. 1 mm of rain on 1 square metre of roof is 1 litre - so for example if a single 15-year event drops 30mm in an hour and you have 50 square metres of roof flowing into the box gutter then the system needs to handle 1500 litres in that hour - ie: the smallest outlet has to manage a good proportion that volume or your gutter will fill up and then overflow.

Residential guttering are usually built for 15-year events, occasionally for 25. This means that if you happen to have a more severe event then you have to make sure that the overflow goes to the outside of the house and stormwater system so it does not cause any damage. These estimates of the occurrence of these events are based on historical data which often goes back just 60 years or less and the risk of the events are based on good science, but are on averages over a long time. So it is quite possible to have two 15-year events within a year (or even within a couple of weeks).

As above, once you have done what is reasonably possible (given access, time, technology and money) to secure the gutter as to size and being fully waterproof, the key is to make sure that any overflow goes where it will do the least damage ie: onto the ground.

Sorry if that is all a bit repetitive.

Bloss

Are you sure aluminium causes gal gutters to rust. I have aluminium flashing going into gal gutters for years and have had no problems.

Aluminium swages are also used on gal wire so I can't see how there could possibly be a problem.

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Originally Posted by mat

Bloss

Are you sure aluminium causes gal gutters to rust. I have aluminium flashing going into gal gutters for years and have had no problems.

Aluminium swages are also used on gal wire so I can't see how there could possibly be a problem.

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Mat,
you sure your gutters aren't zincalume? Zincalume is compatible with aluminium, while I'm pretty sure gal isn't. I also suspect that modern fencing wire isn't "galvanised" but more likely zinc or zincalume coated.

Mick

Another product you could try is sikaflex.
I fabricate aluminium windows and this is used around windows to seal between the frame and brickwork.
it is flexible so it wont crack and if needed can be painted over.
It is also a variation of the same stuff used to hold in car windscreens.
it is by bostitch and sold in 10-12 inch sasuage.

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Originally Posted by commoo

Another product you could try is sikaflex..................
it is by bostitch and sold in 10-12 inch sasuage.

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Actually "Sikaflex" is made by Sika Industries. Bostik make Seal and Flex, Ultra and Matrix amongst others. Bostitch makes nail and staple guns. I've used all of them (plus own a few Bostitch tools:wink: ) and still reckon that no sealant will last 3 years in this application.

Mick

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I'm pretty sure gal isn't

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I don't really understand the chemistry behind it all but galvanising is done by hot-dipping steel in molten zinc. The zinc prevents the steel from oxidising but it does not prevent electrolysis occurring between different metals, such as aluminium, in the presence of water.

As far as I know, the only difference between Zincalume and normal gal is that the coating also contains aluminium. Why that aluminium doesn't react with the steel underneath in the same way, I don't know, but I imagine it is to do with the way it has been bonded to it during the galvanising process.

So, pure zinc-coatings used in galvanising can still allow electrolysis to occur between the steel and aluminium (or other metals). Zincalume to zinc-coated (galvanised) steel can also cause problems (eg. Zincalume roof into a galvanised iron tank). Galvanised steel lintels in contact with aluminium window frames are also bad.

However, Zincalume and aluminium are OK together. I'm sure Bazza would be able to explain why. All galvanised wire is coated with zinc, but it may also have aluminium in the mix, which is why fencing wire and aluminium swages would be OK. I guess.

Unless you know the gutter and downpipes are Zincalume, or unless they are Colorbond, I'd stay away from aluminium.

See the link I posted here:

http://www.woodworkforums.ubeaut.com...ad.php?t=48057

Zinc is sacrificial to both steel and aluminium.

Most downpipes are woefully inadequate to the demand flow. After you get a decent slope, bust out the end, and extend it to provide free-fall beyond your foundation. Can drop into a dry well and/or a French drain.

Joe

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Originally Posted by joe greiner

...............a French drain..........

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Quest Que Ce?

Mick

I think it what we call a "spoon drain"?

"Spoon drain" should work, too. Seems to be varying definition of "French drain." I had in mind a perforated, (usually) corrugated ABS pipe inside a gravel envelope, inside a wrap of filter cloth, all buried, except for gravel inlet basin and exposed outlet. Wikipedia has some discussion.

Joe

Mat

Yep - Depends on whether you have a gal box gutter or Zincalume. Since you said the house was built in 1964 it is highly unlikely to be zincalume (that was only created in 1972). I assumed it was the original gutter so would be galvanised iron. most probably with soldered joints (pop rivets were not all that common in 1964 either and there was no silicon sealer on the commercial market in Oz). Even using silicone sealer you must use the correct one - which are differently formulated for gal and zincalume!

So for a gal gutter keep aluminium flashings clear - lead or zinc is the go. Likewise you should not use zincalume in contact with gal either - as the galvanic reactions (electrolsysis) can cause problems too. Not fast and much slower in dry climates, but will significantly reduce the life of the product with the sacrificed coating.

There are v.good technical data sheets and FAQ on this subject at the BHP BlueScope Steel website:

http://www.bluescopesteel.com.au/go/...hnical-library


Often aluminium flashing has coatings that prevent or reduce contact - older types used tar-based finishes and then plastic. This can be used, but exposed metal at edges or where cut or damaged can still cause problems.

But as I said a 2-part waterproofing compound is probably the best if you can get good access and can clean and prepare before application. Or replace the gutter altogether - but if you do you need to account for the roofing material and follow the tech notes for the product you plan to use.

Re-read my earlier post and from others too - you have a series of issues to fix or minimise your problem - only one of which is the leaky box gutter: a) leaky gutter needs to be waterproofed or replaced; b) capacity of gutter needs to be sufficient; c) capacity of downpipes & stormwater drains needs to be sufficient; and d) you need to have a suitable overflow system to direct water away from the gutters and house in extreme rain or rain/hail events.

A number of posts have suggested how to deal with each.

A bit or work to do - but worth it to save damage to the house.

Bloss

Sorry on the delay. Thanks to everyone for their advice. It is a gal gutter and I have opened the end. The downpipe is 6in by 4in with a spitter. Also I have just laid all new storm water with one line designated just to the box gutter. There are two problems. The first in big storms the gutter cannot cope even though I have opened it up at the end. The other problem is it leaks several months after I seal it. I think I will investigate a two part waterproofer.

http://www.guttsa.com.au/ have a look at this link as they make a liner that goes in box gutters. think there in adelaide. nearly used it once to repair a box gutter but the boss said a $60 tin of bitumous paint was cheaper. gutter still leaks.

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Originally Posted by Woodbear

. . . . There are two problems. The first in big storms the gutter cannot cope even though I have opened it up at the end. The other problem is it leaks several months after I seal it. I think I will investigate a two part waterproofer.

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See my earlier post - use ponding boards/ sheets to increase the effective size of the gutter (if you can't simply replace it with a larger one which is likely to be problematic) THEN do the two-part waterproofing. Good luck - what you have done so far seems the right direction in any case.

Bloss