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Posted: Wed Nov 21, 2007 9:51 pm
by montyron
Waterlogged patio: Can anyone help. We have a yorkstone patio that was laid flat, not on the fall, because a fall would have interfered with the line of our wall-length patio doors. We took advice from an architect on how to do this. He recommended the following method:
Remove panning by breaking up the existing compacted ground
• Lower existing gully to this level
• Lay no-fines gravel (gabion stone?) as a drainage layer
• Cover with a geotextile mat to prevent sand filling the voids in the gravel
• Bed York stone on a weak lime:sand mix
• Joint the stones with a similar weak lime:sand mix
The contractor did the above with the following changes/omissions:
Did not lower existing gully
Did not use a geotextile mat
Added small amount of concrete to the lime:sand pointing mix
As a result there is next to no drainage on our patio – water is sitting inches deep on the surface. The contractor says it is the architect’s method that has caused the problem and that his changes/omissions make no difference to the drainage. The architect says it is the contractors’ changes/omissions that have caused the problem. Are there any paving experts out there who can tell me which one is right? Thank-you.
Posted: Wed Nov 21, 2007 10:41 pm
by lutonlagerlout
Did not use a geotextile mat
if the arch specified it then he must use it
the whole thing sounds doomed to me especially in north london clay
why couldnt a proper drain have been put in?
regards LLL
also a picture would be handy 
Posted: Thu Nov 22, 2007 12:14 am
by matt h
why no linear drain? both appear to be at fault, as the builder should have followed architect spec, and architect should have created adequate provision for drainage
Posted: Thu Nov 22, 2007 7:37 am
by montyron
Thank-you Matt H and Lutonlagerlout. I will try to send a photo later. Re: linear drain. The architect argues that, had the gully been lowered to the level of the gravel as suggested, that would have enabled the water to drain away at that level. As a layperson I can't see how the water would have got to the gully as it is in an out of the way corner of the garden. Both architect and contractor agree that, at any rate, that couldn't happen as the water isn't penetrating the pointing, possibly because the drainage layers are already completely sodden. The water is gathering in a dip in the centre of the patio with the gully the highest point! The architect is suggesting lowering the gully and lifting specific slabs to create a slight fall towards it. The contractor says that's a really big job he doesn't want to take on. Does anyone have an opinion on whether it would work, and is it a really big job? Thanks again.
Posted: Thu Nov 22, 2007 9:24 am
by eazybarra man
As matt & LLL say, both would appear to be at fault.
Drainage should have been catered for.
It is difficult to say whether existing gully being lowered would have catered for drainage without seeing photo.
A new gully or linear drainage connected to existing gully would have been the answer I think.
Even if concerned about the "finished look" of linear drainage " shiny metal grating" there are new types of channel on the market which have a narrow slot on the surface attached to the channel below ground. Looks more pleasing on the eye. Hauraton certainly manufacture this type and others will probably too.
Also the geotextile, as your architect rightly says adds stability and prevents sand moving/filling the voids.The geotextile allows water to penetrate and therefore should not effect the drainage. Hope this helps
Posted: Thu Nov 22, 2007 11:22 am
by Rich H
While the contractor should have followed the spec., I wouldn't have taken the job with that spec! If you pave a surface flat with non-permeable paving, it won't drain. According to the architect's design, the entire area would have to be under water to drain at all!
I would suggest getting a third party surveyor involved to give recommendations. If possible, get the faulty party(ies)' agreement to cover the cost in the event they are found wanting.
I have a bias: architects and designers piss me off royally!
Posted: Thu Nov 22, 2007 5:15 pm
by lutonlagerlout
i was under the impression that permeable paving had permeable pointing
lime and sand is weak pointing but not permeable
i would have thought grit was more appropriate in this instance
whole thing sounds like people trying to be too clever by half and coming instuck
drainage is the first thing you think about with a terrace in this wet country
LLL
Posted: Thu Nov 22, 2007 5:40 pm
by eazybarra man
LLL, Your spot on, unfortunatly a lot of people either dont think about it or dont know anything about drains.
The amount of times I have seen jobs where drainage channels or gullies are installed but not connected is scary.
Posted: Thu Nov 22, 2007 5:47 pm
by dig dug dan
would it not be possible to remove the slabs in the lowest point of the patio where the water now sits, and dig a big soakaway underneath for the water to go into. Use the stormwater cells, cover with geo fabric and infill with gravel,and then install a simple gully recessed into the patio that the water can flow into.
got to be cheaper than ripping up the whole patio and starting again inmho.
Posted: Thu Nov 22, 2007 7:47 pm
by dig dug dan
nice job LLL. and youve used the terram all round. Many poeple don't bother with that!
Have you tried the stormwater storage cells? brilliant in my opinion, and the ground doesn't carry on sinking forever and a day after you have infilled!
you are right about the clay. Similar problem i had in oxhey about two years ago. both soakways filled right up.
Sump pump is the only answer
Posted: Thu Nov 22, 2007 11:57 pm
by lutonlagerlout
Well a 10M by 4.5 M sheet costs about £25 and you get 2 soakaways out of that so its madness not to use it
i have used the cells but they are extortionate and our local bcos do not ask for them yet
cheers LLL
Posted: Fri Nov 23, 2007 10:02 pm
by montyron
Thank-you everyone for all your help. I will show all these posts to the landscaper and see what he thinks of the suggestions. If you don't mind, I will let you all know what he suggests so I can hear your responses. Thanks. Elaine
Posted: Fri Nov 23, 2007 10:11 pm
by James.Q
the ones i did in hatfield had to have something like a dropshaft so could carry out tests
Posted: Sat Nov 24, 2007 4:54 pm
by Ted
My opinion is that the contractor should be competent and should have realised that the arch's design would not work.
This should have been identified at the tendering/pricing stage, but as it wasn't it should have been pointed out by the contractor during construction... the contractor should have pinted this out in writing to you and the arch... the contractor has a duty to point out how the arch's design is not feasible...
So my approach would be to go for the contractor first and then the arch if no progress with the contractor...
A contractor is obliged to build with the reasonable care and skill expected of a competent contractor and that includes building a patio that drains... the contractor was contracted to build the patio so it is his liability...
Arch's often come up with daft designs but my experience (like Rich H says) is that as a contractor you should not build a daft design...
That said you may also have a claim against the arch... you employed the arch to design the patio... a competent arch should be able to design a patio that drains so you should also have a claim against the arch for the money you have paid him...
An arch legally has to have PI insurance and this should hopefully pay out for the fee reimbursement and also if the contractor goes belly up and is unable to pay for the necessary remedial work, particularly if the arch was overseeing the work and administered the tender process....
soakaway
multitrack