Depth of bedding layer

[Neber]

This should be simple to answer:

I am replacing a gravel drive with block paving (50mm). The problem being the sub-base is already there 8" but only leaves me 20-25mm for the bedding sand. Is it essential to have 40-50mm for bedding sand and why?

I really don’t want to have to remove more sub-base as it is already compacted, needs removal etc.

Any advice would be much appreciated.

Thanks

[Tony McC]

We use laying courses just 25mm deep on commercial high-traffic schemes, where channelisation might be a problem, but the accuracy of the sub-base or base course has to be spot-on, otherwise it becomes nearly impossible to create a workable screed.

For driveways and low-traffic projects, 35-50mm provides more of a 'cushion', and allows for minor inaccuracies in the sub-base to be accommodated. 50mm is the max depth of sand that should ever be used; 40mm is nearer to what is actually used on sites.

On your project, I would possibly elevate the levels by 6-10mm so that I could get a reasonable laying course in place, or scrape off 10mm or so of the sub-base and use it as coarse aggregate for any concrete that will be needed.

[Neber]

Wow thanks for the quick reply

The level shouldn’t be so bad as its only 4m² but I'll trust your judgement that it may be more trouble than its worth.

The site can't be elevated as I'm joining to previous edging.

Looks like I may have to remove some sub-base. You say I can use it for concrete, if so, it is scalpings should I directly replace with the required gravel or use less sand in the mix as well.

Fantastic site by the way

[Tony McC]

Just use the salvaged sub-base material as a replacement for gravel in your concrete.

[Neber]

Right, I edged a large patio and the driveway at the weekend and thankfully I recycled some sub-base.

I just have one question before I lay the blocks and finish:

I am a bit nervous about the height of the haunch (10mm) on the edging the car will constantly roll over (from block to gravel). The concrete was laid 24hrs ago, will it be OK to add a higher haunch to the old one, or is it a bit late?

Much appreciated

[Tony McC]

Add extra concrete as and when you need. Using a wet mix, or adding a bonding agent, will help it 'stick' to the older stuff.