Replacing an old cast iron manhole cover

[David Chapman]

Hi,

We have a very old rectangular cast iron manhole cover (approximately

650mm x 495mm) in our front drive which has just shattered and is now in urgent need of replacement.

The nearest size (in galvanised steel) that seems to be available from the local builders merchants is around 600mm x 450mm so it seems likely that the old frame will have to be replaced as well with one that is large enough to cover the hole plus overlap for fixing.

I'm posting this in the hope that someone in the NG with experience of these problems can suggest any better replacement solutions, or offer any hints or tips as to the best way to replace the old manhole frame/cover.

Any constructive comments will be much appreciated.

ATB - Dave

[Onetap]

Hack out old frame, seat new (probably plastic) frame in mortar, make good. I had to do a couple after the car wheel went through a paved over CI cover. Never done it before, I used the tray type with inset paving. I've since had a skip lorry parked on one with no ill effects, so it must have been adequate.

[NT]

Is it possible to drill CI to repair it?

NT

[Onetap]

Maybe, but not worth the effort. It's grey cast iron, it has slag inclusions in it and it is as brittle as glass. A good crack with a hammer will shatter it. CI drain covers are only suitable for pedestrian traffic. The drain covers used now in roads are ductile (spheroidal graphite) cast iron, that was invented in (I think) the late 40s. You can weld cast iron apparently; I tried once and after much preheating and welding concluded that I couldn't weld it.

[Andy Dingley]

Yes - if it's a simple break into two or three and the load capacity isn't required to be too great..

Easiest is to drill and bolt through with 1/4" mild steel plates either side, round head screws with heads uppermost and peen over the nuts underneath. Finish with cold galvanise zinc paint and bitumen paint.

Better is to weld it (electric arc), although this is tricky for CI, especially large CI.

If you want someone else to deal with it, there are Metaloc and others who do stitched repairs in CI. I'm not sure how they'd do something with bending forces on it like this though.

[A.Lee]

It is an easy job to replace the manhole and frame. Go to a better builders merchant, they will be able to get you a similar sized frame. They come in loads of sizes and weight ratings. Make sure you get the weight rating right, otherwise it could collapse again. To replace, get a big hammer and chisel, knock out all of the concrete around the frame, get out the old frame, then make a 2-3" gap all around the outside of the new sized frame. Concrete it in, leave a few days,and you can drive over it again. Alan.

[Matty F]

I made this smaller cover out of flat steel to replace a cast iron cover that was stolen. There's a leg welded under each corner to get the height correct.

[Stuart Noble]

In my case the new frame was a bit smaller, so I had to lay a course of bricks to support one side. If the hole had been deep, I'd have gone for the next size up

[Andrew Gabriel]

I've replaced one which was on a path. Finding one which matches the frame is going to be unlikely, particularly if old. As others said, buy a replacement frame and cover.

One thing I would suggest - get a proper cast iron one. I bought a pressed steel one (3 tonnes, IIRC), but it went poing-ping every time you stepped on it, so I swapped it for a cast iron one (7 or 10 tonnes, IIRC). Didn't cost much more, but make sure you go to a builders yard with a good stock, and not somewhere which just keeps one or two types at inflated prices.

[andrew]

They're expensive but rated to 12 tonnes and it may be worth the risk of buying a 600 x 600 one and cutting one side off.

AJH

[Michael Chare]

Make sure that you buy one that is strong enough to support a vehicle. Some covers are only suitable for pedestrian use.

[Andrew Mawson]

(approximately

available from

experience of

frame/cover.

vehicle. Some

Get a piece of 1/4" steel chequer plate cut to fit your hole and if the loading is great weld 2" angle irons across the underside

AWEM

[David Chapman]

Many thanks to all those who took the time to reply to my posting and offer constructive solutions. Your contributions were much appreciated.

ATB - Dave

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Andrew Mawson" saying something like:

Which is the most sensible solution. Iow, just what I'd do :)

[gsglazing65]

Size of cast manhole cover 565 x 350

[Andrew]

Modern ones seem to be about 25.5 inches by 18.25 inches which is about 648 by 464.