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Posted: Wed Apr 18, 2012 8:47 pm
by bankrupted
Hi,
Going to lay my first blocked paved drive!!
I have had the excavation done and a 100mm MOT1 base laid on top of some broken hardcore. I paid for this work.
The base has undulations not significant, but when pushing the wacker plate you can feel the up and downs. My estimate is that maybe there is a 30mm difference between a peak and a trough.
Is this significant?
Or put in another way how accurately "pond like" flat does the base have to be?
Also is there any problem with not paving for a week or too and exposing the base to the rain?
Thanks
Chris
Posted: Wed Apr 18, 2012 9:11 pm
by GB_Groundworks
when you screed and whack the grit sand it will sort these out but if you want you can rake them and re whacker them till your whacker is bouncing and making a different noice a higher pitched rattle than the low down rumble as its compacting
Posted: Wed Apr 18, 2012 9:36 pm
by bankrupted
Thanks for the reply.
I am going to spade a bit of MOT 1 into the dips and re-wack to reduce the dips, but it's good to know that the sand layer can can take some of these dips out.
Thanks
Chris.
Posted: Wed Apr 18, 2012 10:46 pm
by digerjones
if it was me, you want to get the stone base as good as you can, 30mm is not bad but could be better. if you have your kerbs in, string a line across and dip it. [measure down] you can buy granite dust to trim the stone more exact. you need the stone as good as you can get it so the laying sand is the same depth all over, so it settles at same rate.
Posted: Thu Apr 19, 2012 6:44 am
by local patios and driveway
Also, dont worry about leaving it out in the weather, infact i would argue a good rain on top of your base would only help to further improve the base
Posted: Thu Apr 19, 2012 2:05 pm
by bankrupted
Great all good news do far.... But...
I am just finishing off wacking and spreading a little MOT1 left over to fill in any dips. What I am finding is that is some places the MOT1 has compacted well, but in others it seems to be less so.
On this picture here...
http://www.pavingexpert.com/images/blocks/step-by-step_exc02.jpg
The water pooling was similar to mine as after excavation we have had crap weather this week. The hard core (about 1 bricks thinkness was spread out evenly an then rolled over with the minidigger. Basically this just pushed it down into the mud. MOT1 then on top. But we only had about 6~8 tons of hardcore to cover the 100m2 drive. (the hardcore was the old drive paving)
Now as it's still raining on and off, I am getting pooling of water in places on the base and as I wack it I get the feeling that I am basically pushing the whole lot (hardcore and MOT) further into the mud.
The base seems reasonably good but I don't feel I am going to be able to wack it 8 or so times until complete compaction as it's pushing it into the mud
Maybe I worry too much!!!
Has my contractor done anything wrong? Excavate 200mm, some hardcore and then 100mm of MOT 1. No geotextile or examanination of the ground (which was soft) after the 200mm excavation.
Should I stop wacking and wait until we have a few dry days?
Cheers
Chris
Posted: Thu Apr 19, 2012 7:02 pm
by Dave_L
If the ground was soft then it really should have been dug out to a greater depth to a point where the ground conditions improved.
What sort of 'hardcore' was put down?
Posted: Thu Apr 19, 2012 7:33 pm
by bankrupted
Smashed paving slabs/ crazy paving broken up to quite small pieces, with a mixture of concrete that was also broken up.
Posted: Thu Apr 19, 2012 9:44 pm
by seanandruby
your hardcore should be crushed, your mot should be +/- 5 to 10ml, otherwise your going to have 70ml sand in places, 70 ml is to deep, you'll get differential settlement. You should also have dug, (as dave suggested ) deeper to take out the spongy sub soil. Preperation, preperation, preperation, it's never to late to do again, if you want peace of mind and a good job and cheap :;):
Posted: Fri Apr 20, 2012 8:19 am
by bankrupted
I measured some of the dips and they were in fact about 20mm, which I have been filling with more type 1 and compacting. So I am confident to get it down to 10mm or less.
Compacting has been done to completion in most places. It is just that my soil must be mainly clay. When it rains very heavily the water sits on the grass, until it disperses.
I am looking for perfection, and I think I am overly concerned, I queried simply because in some areas compacting the type 1 was just pushing water up from below, not necessarily pushing the hardcore and type 1 into the mud (I hope)
And since it rained really heavily yesterday I had lots of standing water on the base, (took about 1 hour to disperse after rain stopped). So I imagine if I went straight out and started compacting I would see water start to surface as it's squeezed up. This is basically what was happening before in the more softer area, hence my concern.
I am pretty sure that had I had the base put down after a few days of completely dry weather and it remained dry over the construction and compacting this issue would never have been raised.
I was just hoping to gain more info and really understand if I have a problem from the professionals here.
(Have to add again that I paid a ground works contractor for this work, just that I was around to help out so I saw what was going on and kept the wacker for a few days afterwards to really get it compacted as he wasn't going to go over it 8 times in both directions!!)
