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Hardcore base or concrete pad?

When specifying paving, is it common practice to spec with a concrete pad foundation, instead of just consolidated hard core base?

I am getting mixed advice - some landscapers say just hardcore is fine, some say always use concrete as won't move!

What is the general consensus? What should I put in my spec? Or should it be site specific?

 

Many thanks, Amy

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  • It all depends on the paving your laying, pressed slabs you can get away with laying straight onto the soil, not most professional way but saves money for the customer if needs be, I always lay on compacted hardcore then on dots and dabs, but when laying the like of sand stone I lay it on a bed as you see where the cement is underneath due its being porous. laying straight onto a bed only works if the ground below is stable its will sink and crack

    I always started with a compacted base and never just on sand
  • A good point of reference is pavingexpert.com  They have all the answers!

    As a rule, concrete over type1 or similar if it is expensive paving (granite, sandstone) and/or the substrate is likely to move.

     

    Good prep saves having to come back!

  • 99% of the time i lay paving on a full bed of mortar on appropriately 100mm of compacted type1and never get any problems for domestic paving

    When laying paving on areas of  ground that is heavy clay it is advisable to lay on a reinforced concrete pad as clay moves around when it expands and contracts with its water contents

    Cost is always an issue, and a concrete pad cost more but if you want a  100% guaranteed for it not to move laying on a reinforced concrete is the way forward

    Other options if the ground is soft or sandy is to put a heavy grade geotextile membrane under the stone (not a planting membrane) .you can also increase the depth of stone and the size using a 75mm crusher run as a base and going over the  top of that with a 38mm type1 . Also compact with roller instead of compacter plates makes a big difference.

    There are lots of variables with ground conditions how heavy the traffic is going to be before you start laying paving

  • Many thanks for all this information, really helps.

    Reassuring to realise that my spec was ok, and that could go with a belt and braces options with a concrete pad - where required and for certain site specific situations if needed. Thanks!

     

     

  • Concrete base, approx 100mm depth, slabs bedded on mortar.  Dots not a good idea, especially with the thin Indian sand stone, which is only around 25mm thick.  

  • I've never put paving down over concrete in my life and never had any problems. Ground that heaves can also move a concrete slab!

    We put down a porous membrane at formation level followed by 100-mm of hardcore.  Paving should always be laid on a FULL mortar bed. Spot bedding will eventually fail for a variety of reasons.

    Dave

    www.the-gardenmakers.co.uk

  • Dont think I'll be changing after 35 years Dave, we are a London clay area and have always felt safer with a solid base, reinforced if necessary!  

    Dave Sewell said:

    I've never put paving down over concrete in my life and never had any problems. Ground that heaves can also move a concrete slab!

    We put down a porous membrane at formation level followed by 100-mm of hardcore.  Paving should always be laid on a FULL mortar bed. Spot bedding will eventually fail for a variety of reasons.

    Dave

    www.the-gardenmakers.co.uk

  • Colin,

    Warwickshire clay here - the farmers call is 'mans land'. Don't think i'll be changing after 25 years either!

    Dave

  • i always put down a 100mm bed of compacted scalpings, a weed suppressing membrane on the scalpings,and the the slabs will then be laid on a solid bed of wet mix sharp sand & sand mix concrete, never lay slabs on dot & dab as they will always move, and in my opinion if you lay a patio on dots & dabs and then it starts moving you will never get another for that person

  • Just out of interest why the weed membrane Phil?

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