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Posted: Thu Sep 11, 2008 3:17 pm
by ineverdidit
I have a front driveway 80m² which is about to be block paved. The sub base is mostly clay and I have obtained three estimates from companies on the Marshalls and Interlay Registers. This is where I need advice.
1 Estimate;
Clear a depth to 200 mm lay weed membrane sheeting, 100 mm of MOT Type 1, which is the base for block paviours.
2 Estimate
Minimum excavation depth 250mm, minimum sub-bas 150mm MOT type 1.
3 Estimate
Excavation depth 200mm, lay terram sheet followed by 4¨ lean mix concrete and consolidate...
As price is not an issue, (they are competitive) which one should I choose?
Thanks in anticipation of any replies.
Posted: Thu Sep 11, 2008 5:57 pm
by Pablo
Estimate 1 not enough depth of type 1
Estimate 2 Sounds fine
Estimate 3 WTF is he talking about. Prize idiot. Are you sure he was a registered contractor.
Posted: Thu Sep 11, 2008 6:21 pm
by Tony McC
The one you feel most able to talk to on a human level. Unless you are relaxed and able to get on with your contractor, any little changes or modifications you require will be that bit more difficult.
Posted: Thu Sep 11, 2008 6:54 pm
by GB_Groundworks
Pablo wrote:Estimate 3 WTF is he talking about. Prize idiot. Are you sure he was a registered contractor.
playing the devils advocate i would assume he is talking about cbm
LEAN CONCRETE / CEMENT BOUND MATERIAL (CBM)
However the ROADBASE (base) can also be, and quite frequently is, LEAN CONCRETE.
But I am afraid lean concrete is no longer called lean concrete, it is called CEMENT-BOUND MATERIAL.
CEMENT BOUND MATERIAL CATEGORY 3, i.e. CBM3
or
CEMENT-BOUND MATERIAL CATEGORY 4, CBM4, being the materials usually used as roadbase.
CBM4 being stronger than CBM3.
used in road/motorway construction and often laid by paving machines forms a good sub base.
Posted: Fri Sep 12, 2008 4:51 am
by lutonlagerlout
that's correct, but standard block drives are flexible ,roads are not.
i know of 2 firms that use lean mix as a sub base rather than type 1 and TBH the results look fine
however block paving on the whole should be on a flexible base
whats the weed control fabric for? they will have a job getting through 200mm of paving?
i would say guy 2 as he advocates a proper dig but ask him to use terram,which is a geo textile,not a weed control fabric :;):
LLL
the best way is to look at 3 of their recent jobs 
physically i mean
Posted: Fri Sep 12, 2008 12:04 pm
by Tony McC
CBM or lean mix as a sub-base for residential driveways is, in theory, acceptable but I have two concerns regarding its use:
1 - it is usually installed by contractors who are incapable of installing a proper flexible sub-base. They have had problems in the past with their installations and fail to recognise the fact that the little 20kg plate compactor they bought off EBay is not capable of compacting sub-base material. So, rather than invest in a decent plate or a roller, and/or get educated as to how to construct a suitable sub-base, they opt for a concrete base as a cover for their lack of genuine skills.
2 - there is rarely any consideration given to drainage of the laying course. Many concrete bases will be impermeable; when water gets into the laying course, there is no route to ground, so the sand becomes saturated, it fluidises and the blocks begin to pump.
There are instances were a concrete base is warranted, but they are the exception rather than the rule. However, as long as some provision for laying course drainage is included, there's not strictly anything wrong with them.
Posted: Mon Sep 22, 2008 6:43 pm
by Slabba.
Estimate 2 is the only choice for me.