have we caused damp? how do we fix it?

[Frazzled11]

we laid a patio at the bottom of our downward sloping garden about a month ago. the patio ended up about a brick below where the ground was origionally and 3 bricks clear of the damp course. we built to the garage at the bottom with the sub-base and sharp sand and left about a cm of block paving sand to the wall before the slabs. it generally slopes towards this but in all fairness the front part slopes away (it looks ok to the eye and is only slightly off on the spirit level).

after a weekend of heavy rain and despite an ok day today, one brick layer above the patio is wet looking with some funky white lines. even the garage that has a good 15cm of gravel between the bricks and patio ( one area of patio is between two garages) is looking soggy.

do we need to pull it all up start again? slope it away? paint some protective stuff on it as still bellow the damp proof.

please help, it killed me doing this and can not afford really to get anyone in and really dissapointed seem to be having probs. View media item 35641

 

[PhillCO2]

I'm no expert on the subject, I would say it may have been advisable to put a french drain of orts on the house side of patio using gravel however if the highest point of the paving is below the DPM of the wall and the tide mark has not progressed higher than the DPM then generally you should be alright I would think, that's what the damp proof is there for.
The tide mark you are seing is likely because water is not draining as fast now due to the paving.

I've had my property for around a year and it has an absolutely hideous patio that I am currently demolishing in favour of decking. This was built well above the DPM but the builder had made a somewhat shoddy effort of putting extra DPM on the outside of the wall before filling in. The new DPM stopped below the level of the paving and I haven't noticed any issues with damp inside despite the property being vacant for over a year before I purchased it.

I'm sure someone here will be able to advise you from greater experience however.

 

[r896neo]

hi firstly, sorry to hear your woes.

Regardless of height of dpc etc all hard paving/patios etc must fall away from buildings (even if its only the first flag that does) and it's a pretty major oversight to get this wrong? of course in some scenarios a drainage channel along the wall is more suitable.

Also I am hesitant to tell you now as it's a bit late but flags like yours really need to be layed on more than just sand, how are the edges finished?

Lastly, you don't really want a channel of sand next to a wall as it holds water, better off changing this for gravel if possible.

 

[freddiemercurystwin]

Aye you may as well wait until the sand begins to gaive way and the slabs start going a bit wonky and re-do it falling it away from the wall and a french drain against the wall. Still if you're gonna use sand at least you chose the right sort.

 

[Frazzled11]

thanks for your advice....i have more questions and some answers and clarification if this is ok.

the first flag line against the garage is flat. should we change this? how much of a tilt away does it need?

do you need to line french drains or would replacing the sand under the slabs by the wall with gravel work? we have a lot of clay in the soil would a french drain not cause a soggy patch somewhere else?

i have seen a hex drain that has a snorkle type appearence of a cm to drain, are these any good? would it solve my issues? we do have a a drain right in the corner draining the guttering from the garage but fear connecting may be out of my experience abilities. is it difficult?

to respond to your questions, the wall in the border for one part, the rest is yet unfinished really. the base is 15cm wider than patio slabs and at moment just has gravel around, we intend to concrete edges in when we knew we were not going to have to make any adjustments, these edges currently are rock solid. we had also thought of using aco border guard. it is build on 50mm depth sharp sand with landscape fabric below it. All is on a base of 75mm of MOT Type 1 sub base. I'm only hopefully a bit of a muppet and tried my very best.

Plan B is shift the patio 30cm forward with a re-jig of back stones to the front if we extend the base, put in concreted in paving edging about 10-15cm from slab edges (or would it be better to go completely against)? and put soil back in the 15-20cm actually beside the garage (leaving MOT base but removing all the sharp sand) with gravel covering all the surface gaps. lots of effort but would this be the best thing to do? .... i can take it.

leaving it would scare me - its mainly not my garage that is affected!

final questions. this photo is my garage and is the slightly higher side. is this because of the sand against the wall as the base is the same here just with a further membrane on and decorative gravel? how big of a strip of sand do i need to replace with gravel?

again i really appreciate all of your time and thoughts. View media item 35674

 

[r896neo]

Hi you post is quite long and a little confusing so i'll just throw out some 'facts' (at least they are in my opinion) and if you have anymore queries just ask.

Free edges of paving that are not restrained by a kerb must be layed on mortar otherwise the slabs will gradually move around and spread.

Flags next to a wall of a building must fall away from said building, as long as it falls it doesn't matter how little.

Sand beside a building is a bad idea as it holds water a so a french drain is better but it is really not needed if flags are tight to the wall and fall away. A french drain is sometimes used to overcome problems with dpc heights but if your 150mm below dpc and the flags fall away that is perfect.