The Brew Cabin

Posted: **Fri Oct 05, 2007 4:22 pm**

I'm looking for a recessed manhole cover to put down on my 480mm x 830mm manhole on my driveway.

Those measurements are of the hole.

My question is what do the dimensions on the covers mean? Do they refer to the hole they will cover with some overlap for the cover to sit on the ground?

The hole seems quite long as the biggest as yet recessed cover I've seen was 600x450mm.
The old cover used the concrete block in the pictures to reduce the size of the opening (I've removed the top course of brickwork as it will be too high for the new driveway) to enable a smaller cover to be fitted. Am I ok in using this method again or do covers exist to suit my exact needs?

Been looking at http://www.clark-drain.com/resourc....-ssf-14 but I'm a bit confused as to exactly what size I need. Can anybody offer some advice?

Posted: **Fri Oct 05, 2007 4:51 pm**

quoted sizes of covers are for the clear opening e.g. a "Standard" 600x600 c/f means that when open the inside dimensions of the "Hole" are 600x600mm

for a hole of your size the closest stock size is a 600x900mm, for a recessed block paving cover this is likely to be the thick end of Â£100, go for a non standard size and you are talking megabucks, plus extortionate carriage charges. 600x900 is big for a single recessed tray, so this will probably be a two part cover.

you'll need a set of lifting keys too...

Posted: **Fri Oct 05, 2007 5:52 pm**

what we would normally do teddy is get a standard size cover then corbal over the last 2 or 3 course of brickwork to make it work
when corballing never overhang more than 25% of the bricks size at one time
so in practise this is 50 mm of the length or 25 mm of the width
hope this helps
LLL

Posted: **Fri Oct 05, 2007 7:27 pm**

Excellent. So if I dismantle the existing brickwork I can build it back up with each course slightly overhanging the one beneath. That idea sounds good to me.
I can get the width right with that. I've never heard of corbelling before. I've learnt something today!

I'll reuse the existing concrete block to reduce the length as it seems to have been ok with the previous cover. I suppose it's technically a bodge but it should be ok.

Posted: **Fri Oct 05, 2007 9:18 pm**

corbelling is no bodge teddy ,look here
its thousand of years old and i have seen loads in manholes
makes sure and cut a bit of ply in the bottom while you are working,dont want any hardcore in the drain run,do we?
cheers LLL

Posted: **Fri Oct 05, 2007 9:31 pm**

I wasn't referring to the corbelling as being a bodge, I was meaning using the block of concrete to reduce the overall length was a big of a bodge.
Using corbelling to slightly reduce the chamber width is a great method.

The Brew Cabin

Recessed manhole covers. how are they measured?