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Posted: Wed Nov 17, 2010 3:36 pm
by Praesepe
Hi guys
hope you can help.
My son offered to extend the block paving shared with my neighbour in 2 areas, one for each household. The total area for both is 18 square metres.
My neighbour's side has gone well and he has extended the herringbone up to the new haunching. He will complete the darts and slips this weekend. Lovely job.
On our side there are 2 softspots in the scalping layer are compaction 3 times. One area, close to the haunching, I am not worried about since it will never be driven on. Hover, the other spot is just over a metre diameter still moves when I walk on it ( 19 stones, if that's important)
We are on heavy clay in this area but the scalpings are probably more than specified as the lad got carried away with the excavator. ( 1 extra 4 yard skip and then 2 extra tonnes of type 1 to backfill)
Can anyone suggest our options? Suggestions on weight reduction will fall on stoney ground.
Posted: Wed Nov 17, 2010 5:12 pm
by dig dug dan
firstly, when you say scalpings, your not talking about road planings are you?
secondly, you say there is a good layer of them, but has it been compacted in a layer at a time, or was it all put down and then compacted?
it sounds like you might need to dig the soft spot out and add more hardcore.
I dare say that had terram been used, this problem could have been avoided
He will complete the darts and slips this weekend.
Not little slithers i hope?? ???
Posted: Wed Nov 17, 2010 6:08 pm
by lutonlagerlout
the main thing with any excavation for block paving or patio is to asses the sub grade i.e. the mud
if it is soft it must come out
if the ground is generally clay (as it is here in luton) we always use terram to stabilise the subbase
what kind of compaction are you using?
also darts and slips are a big no no
see this page for
info
i just did a load of cutting in today will get a picture tomorrow weather permitting
LLL
Posted: Thu Nov 18, 2010 10:30 am
by Tony McC
If a sub-base is moving when *anyone* walks over it, regardless of their weight, it's WRONG!
Excavate, put in a stabilisation membrane then re-construct the sub-base, in layers, as described here
Posted: Thu Nov 18, 2010 4:32 pm
by Praesepe
Thanks guys
first I am not an expert so forgive me if I use the wrong term.
Clarifing some of the points made
I bought Type 1 scalpings according to the invoice from SEHMI
We did noy use a membrane which is often shown as optional.
The clay did not move when we finished excavating.
The scalpings when down in 3 layers compacting after each load.
We used a medium weight plate compactor.
We seemed to draw up the water during the compaction process.
When I said darts & slips only 2 are smaller than half a brick. This is unavoidable due to this is an extension to existing paving and the lie of the land.
The existing block paving has been down 22 years and did not have a membrane. It did have scalpings & sharp sand in the correct proportions but there are minor dips in a few areas.
Thanks for all the advice.
Posted: Thu Nov 18, 2010 11:33 pm
by Big Phil
without sounding pedantic, scalpings in quarrying terms is the material removed from blasted rock that is deemed of poor quality and can contain shite and clay. the term is also used in other crushing operations to remove the unvalued material. You'd have a scalping screen in before processing. anyone selling 'scalpings' i would guess would be poorer quality material and not really a proper type 1 unless it has been tested to prove it's compliance.
Posted: Fri Nov 19, 2010 12:17 am
by GB_Groundworks
im with big phil on this, scalping are the cheap crap left over, and type 1 scalpings is a bit of oxy moron.
Posted: Fri Nov 19, 2010 10:44 am
by Tony McC
But it comes back to something I mentioned a few days ago: terminology. Look at how many people talk about 'cobbles' when they are actually referring to setts.
In some parts of England, notably that London and beyond, the term 'scalpings' is used to refer to almost any crushed stone. Given that Praesepe was sold "Type 1 Scalpings" I'd guess that it is genuine DTp1, otherwise why use the term "Type 1", but the BM has put scalpings rather than simply "stone". There is no such thing as Type scalpings - there is scalpings, and there is Type 1, but the two are sort of mutually exclusive.
The methodology outlines is OK except for one point - the use of a "medium weight plate compactor". I know this is something else I've rattled on about previously, but according the the BS, the *minimum* plate mass for compaction of sub-base material on a category IV pavement (a driveway or patio) is 80kg. The vast majority of contractors, and nearly all DIYers end up using a plate of maybe half that mass, which is why we see so much settlement on completed driveways.
Whenever possible, a vibrating roller should be used to compact the sub-base. If you're lucky enough to own or have access to an 80kg plate, all well and good, but even one of the most popular plates, the Wacker WP 1235A has a mass of only 60kg. These lighter plates may be suitable for compacting laying course (all of 40mm deep) and doing the final consolidation/jointing of the blocks, but for sub-base compaction, they are way too light.
Incidentally, for Category I and II pavements (public highways) a plate of not less than 200kg mass is required.
Posted: Fri Nov 19, 2010 12:33 pm
by Bob_A
Praesepe wrote:.........I bought Type 1 scalpings according to the invoice from SEHMI
Here's their website http://www.sehmis.co.uk/our-branches
Seems a reptuable company to me
Posted: Fri Nov 19, 2010 8:35 pm
by lutonlagerlout
around these parts everyone calls type 1 *MOT*
nothing else
and grit sand is never called that,its always "screeding sand or riverwash*
LLL
Posted: Fri Nov 19, 2010 9:48 pm
by digerjones
grit sand round here is called sharp sand or concreting sand, well thats what i call it. mot is mot or 40mm down
Posted: Sat Nov 20, 2010 10:26 am
by Tony McC
lutonlagerlout wrote:around these parts everyone calls type 1 *MOT*
...well, it's only 31 years since the MoT became the DTp, and we all know how badly the building trade copes with sudden change!
Posted: Sat Nov 20, 2010 1:19 pm
by ilovesettsonmondays
im scared to ask for sand down south .a northerner trying to buy sand down south can become very complicated. 
Posted: Sun Nov 21, 2010 11:23 am
by Tony McC
ilovesettsonmondays wrote:im scared to ask for sand down south .a northerner trying to buy sand down south can become very complicated.
...it's like asking for gravy with yer chips.
They know what you mean but can't understand the need! 
Posted: Sun Nov 21, 2010 1:48 pm
by ilovesettsonmondays
aah tony your right not much call for gravy and chips.they are still learning how to cook chips down here.totally diff to the north .too white down south .