Driveway Block Paving

[Mahmud]

Hi,

I think we have made a big mistake listening to a builder. We are having a new driveway of block paving. The builder suggested to have concrete first and then sand and blocks on top for strength and for avoiding grass coming out of the blocks. But now we are extremely concerned about water being trapped in the sand between the concrete and the blocks. Any suggestions?

 

[JohnD]

what is the cause of this concern?

 

[MattChan]

Not sure if the information here: http://www.pavingexpert.com/blokbase.htm is any use to you?

 

[^woody^]

These ****** will tell you anything for more money

There is no need for a concrete sub-base on a domestic drive. None at all.
The idea of a concrete base is to deal with heavy and prolonged traffic loads, but yes water will be trapped between the blocks and concrete base if it cant drain.

Our city centre had significant block paved roads done in the 80's and it was hard-cored, concreted and then clay paved. Within months, there were ruts where all the busses stopped and ruts/ridges at bends and junctions where the blocks had moved sideways. All this was because of poor design/drainage. But the clerk of works was more concerned that all the cuts were good and everything looked nice from above

 

[Mahmud]

Yes, but the questionis what can we do now?

Do we dig out the new concrete floor (approx 12 X 8 meters) and convert this into hard core and then sand and blocks on top?

or

Dig out chanels to allow water to pass through? but then how many chanels

or any other suggestion?

 

[^woody^]

Drill 25mm holes in it or crack it.

I assume there is a hardcore base below the concrete to allow draining to the sub-soil? Also that there is a fall in the surface level?

Or if the blocks are laid in a bed such as mortar or a sand/cement screed, then it will set solid and would not move when wet. This may be your best option.

 

[Mahmud]

There is is no hard core under the concrete floor and I am thinking that if we crack the concrete then hope that this will act as hard core and simply lay sand and blocks on top?

The newly laid concrete floor has a slope towards the building where it meets newly laid water channel(s) directing the water into a single channel previously there in front of the garage which directs the water into the main guttering.

Alternatively if the blocks are cemented on top of the concrete floor then surely it would not be possible to compact the blocks to a smoother surface finish, would it? i.e. there is a danger of blocks being cemented unevenly.

 

[^woody^]

You would lay the blocks level, and they set level. Or add cement to the sand base, whack them down, and it dries solid

The problem with cracking the concrete is that there is the risk that rainwater concentrates at certain points below the concrete and then this softens, and the pieces of concrete tip or sink. Normally, hardcore is flexible and accommodates slight movement or settlement, but large pieces of concrete don't have this quality.

It may pay you to get someone to actually look at it and make an assessment on the best course of action.

 

[Mahmud]

Hi ^woody^

Thank you as I really appreciate your comments.

With your last suggestion if some cement is mixed with the sand does it mean actually add water and make it a proper mix and then lay blocks on top or add cement to sand while the mixture is still dry and simply lay blocks on top?

On the other hand if the blocks are laid with hardly any gaps in between then is there still a risk of water passing through?

Is there any grout which can be used to spread all over the finished floor which hopefully will seal the gaps between the blocks and prevent the water going through?

 

[r896neo]

You could lay them on semi dry as woody mentioned.
You dont compact them to to get them level with this method which is why you need a plasterer or skilled person to do it in order to get it level.

Laying such a large area of semi dry would be challanging and expensive, its normally used on small platforms or large steps etc rather than the usual sand method.

IMHO the best way will be to remove the concrete altogether and redo it the standard way as i reckon this will be cheaper to do than the semi dry method and you will find it difficult to get someone to take over mid job and rely on others work as a base.

 

[Mahmud]

I have already spent enormous amount of money on 6 skips to first remove the old concrete and also soil from the surrounding garden. And even then there is still some concrete to be disposed off. If I now dig out the new concrete then it means spending further money on at least 6 skips plus hard core and not to forget the labour.

Therefore, I am thinking that I should ask my builder to mix the sand and cement, compact it as the sand is normal compacted and simply lay blocks on top. Then hope that the water when tips through will dry up the sand and cement mix and eventually all passage for the water will be blocked. If this does not work then perhaps dig out the floor in years time which may be same as doing it now, hopefully I would have saved some money by then. I live in a nice area and therefore don't want to face embracement. What do you think?

 

[JohnD]

Perhaps I am stupid but i haven't seen you say why you are concerned. have you noticed the bricks floating away or something?

Or are you just worried that maybe one day they might?

 

[^woody^]

You've only got a couple of suggested solutions - either of which may work, or there may be better ideas. It would be a shame to waste some more money on it now, but you really need an idea of the best way to proceed

Post on the paving expert forum as linked above, and see if you get any more suggestions.

Or have you posted in the gardening forum - or send a PM to Thermo as he does a lot of groundwork, IIRC

 

[r896neo]

Yea i agree to PM thermo, I reckon from your replies that the best way forward would be to lay them on a semi dry base which is uncompacted but make sure you get someone who has done it before and has the skills to do it as it needs to be floated very flat and layed at the right time in relation to it setting.

100m2 is going to cost a fair bit for the cement though!

 

[Mahmud]

I am sorry to be very ordinary, can someone explain what is PM to Thermo please?