Repair of cracked cast iron guttering

[benmc]

All

We have a problem where the guttering is leaking and dripping onto one of the brick buttresses and making the inside wall damp.

I have just been up on the roof and have found a 30cm crack about 4 mm wide running along the cast iron guttering.

Next year I hope to remove all the guttering and renovate/paint etc but in the mean time I need to repair this crack.

What's the best was to tackle it? Silicone?

Please Help

Ben

 

[Hatster]

No idea on repairs, but someone (I think it was Jon Maine) recommended a very good value source of cast iron pipes to me if you want to replace that one straight away - Europipe is the name, and they have a website.

 

[Feltwell]

For a temporary fix, roof and gutter seal will be better than silicone - like this:-

http://www.screwfix.com/prods/67521...?cm_re=SEARCHPROMO-_-ROOF GUTTER SEAL-_-67521

That is quite a wide crack so you may want to stick something like Denso tape (available from any builders merchant or Ebay) underneath, then fill the crack above with the roof and gutter seal.

This is a temporary bodge - the only permanent repair is to replace the cracked piece. Do it well though and it will last until next year without too many problems.

 

[still_adrianth]

JB Weld is very good stuff, too. Not well known in this country, but miles better than products with similar claims that I've tried. I've used it a few times on car engines, and it actually works (high adhesion, strong but no brittle, machinable, etc.). Has saved me a lot of money. Only place I've seen it on sale in this country is Halfords. Feltwell's trick with tape underneath until it sets, and it might last even longer.

Any metalurgists on here? I've just been googling on crack propagation in cast iron, and it's interesting. Is there any chance of an easy solution stopping a crack once it's started?
Even if stresses are reduced by adding more support after the above bodge, will thermal expansion/contraction always make the crack carry on getting longer?

Just curious - my main gutter problems are joints between plastic and original because previous owners didn't have the benefit of PPUK forum...

Adrian.

 

[Pford75]

For a very temporary repair, I would use bitumin backed foil roofing tape. this can then be gently warmed with a blow torch as it is applied to improve it's adhesive tendancies. The sealant type solutions will be prone to dropping through the crack.

If you can get to the gutter easily and you dont mind the cosmetic impact, I would apply the tape to the underside of the gutter first....then use roof seal in the crack and then apply tape to the inside of the gutter

 

[Moo]

Is there any chance of an easy solution stopping a crack once it's started?

My grandad's solution was to drill a hole at the end of the crack.

 

[Feltwell]

My grandad's solution was to drill a hole at the end of the crack.

And your grandad was spot on! The theory I believe is that cracks propagate, i.e. extend, because a force is being applied to a very small surface area - the end of the existing crack. If you make that area larger by drilling a hole, the force is trying to apply itself across a larger area of material and so is less likely to continue to break.

I've seen this technique used with plastic welding on motorbike fairing repairs and it does work. I also heard that this technique is used on light aircraft - a hole is drilled at the end of a crack before a repair is made.

I'm no materials scientist though so if anyone has a more expert knowledge I'd love to hear it.

 

[benmc]

I had to use Silicone in the end. I will get up on the ladder again this evening and check it is watertight.

Thanks

Ben

 

[still_adrianth]

I'm no materials scientist though so if anyone has a more expert knowledge I'd love to hear it.

Good to hear that the hole-drilling trick works: that rings a bell. With a knowledge based entirely on the first few google hits, the structure of cast iron is v. interesting and still being investigated.

The paper, "Gray cast iron primary structure detachment crack propagation resistance," 2008, starts off with:

When gray cast iron crystallizes, a structure is formed similar to that in a fibrous composite: a strong dendritic framework which as it were reinforces the less strong
eutectic matrix. On the other hand, gray cast iron as a constructional material resists only compressive stresses quite well, but has poor resistance to tensile ones. The failure resistance of cast iron under tensile stresses can be raised if the primary structure resembles that in an artificial composite and is capable of deflecting the path of a detachment crack from normal by including additional volumes in the work of failure. [dodgy translation?]

Wikipedia said: "Cast iron usually refers to grey cast iron... Grey cast iron is named after its grey fractured surface, which occurs because the graphitic flakes deflect a passing crack and initiate countless new cracks as the material breaks" (but the graphite gives many nice properties).

I haven't a clue how the graphitic flakes relate to the strong dendritic framework. Call for "Iron-mad" Wilkinson!

Be this as it may, wacking a bit of silicone on for now sounds like a good call!

A.

 

[benmc]

Just to let you all know.

I siliconed the crack from both the top and bottom with Dow Coring clear Silicone on Sunday morning. I got back up on the ladder last night and tested. Looks like it is watertight. I hope it holds for 12 months.

Ben

 

[Feltwell]

Just keep an eye on it. If it does fail I'd use the roof & gutter seal rather than more silicone - it's a sticker substance, seems to be tar based, that never really sets fully. Silicone does set, I think it will degrade more quickly and the seal with the gutter is more likely to fail.

 

[Schoolmarm]

I agree, the silicone will be there in a perfect strip but not stuck to the gutter.

 

[benmc]

Thanks - I will keep a close eye on it

 

[Schoolmarm]

Sorry I meant to say it will be stuck now but will part company after lots of sun and rain.