Below is the layout of my patio and the context

The patio settled and now moisture collects at the base of the wall causing efflorescence on it and small cracks in the cement coating at the base of the wall. These creack seem to be always wet ...

As you can see there is a raised deck on the patio and the main problem with this is that the excavation needed for a french drain will reach the base of the 4x4s that support the deck platform. The french drain will be installed under the patio like in the picture below and after that the pavers will be reset

enter image description here
At this point I have two choices:
1) dig along the wall and stop when I reach the first 4x4
2) dig 2 feet away from the wall and go all the way under deck to the garage

Which solution would you recommend?

The area between the deck and the garage has no water problems For a full size picture click here

enter image description here

  • Which end is your lowest grade, and how low does it get beyond the patio? The question is asked so the water will have an easy route to drain below grade. You do not want to simply put a French drain in and have no place to go...
    – Jack
    Oct 28, 2014 at 12:54
  • Highest point is the North West corner of the patio. I measured the level with this rona.ca/en/laser-level-set and a regular level that has inches/centimeters marks on the side. Let's number the patio corners starting for the corner that is close to the house & garage junction. That would be number 1 and we go clockwise #1 is the highest point #2 is below #1 #3 is below #2 and above #4 In other words the corner of the house that is at the bottom of the diagram is the lowest of all. The patio was designed to drain to #3 but no special drain or channel was built
    – MiniMe
    Oct 28, 2014 at 13:11
  • There is a very good site www.pavingexpert.com which I started to read more seriously during the last two days. After reading some of the pages of this site I am beginning to suspect that my problem could be actually fixed by resetting the pavers to the original position which should make #4 higher than #3 but lower than #1 and after reapplying the polymeric sand the water should find no way to the sub base and to the wall anymore
    – MiniMe
    Oct 28, 2014 at 13:18
  • The french drain might be an overkill for this. I still have to determine if the soil under the patio was graded correctly. How do I do that without turning the entire area upside down? I will have to reset the pavers for the entire 177x(208+40) area of the patio and to reapply polymeric sand on the entire patio (which means removing what I can and filling back with polymeric sand) I am afraid that digging a trench so close to the wall might actually aggravate the problem when the french drain or the patio fail again in 10 years or so
    – MiniMe
    Oct 28, 2014 at 13:23

2 Answers 2


If you're going to pull up pavers to install a french drain, you might as well just pull up all the pavers and get the slope correct instead.

A well laid patio should naturally shed water via its pitch. The ideal solution is to pull up the pavers, re-grade the base layer (should be sand directly under the pavers) and then lay it all back down...perhaps with a slightly exaggerated pitch this time.

If you insist on a drain, I wouldn't bother with a french drain and instead consider a surface drain:

enter image description here

It'd be a lot easier to install.


If water collects there because of a roof with out a gutter, it would be wise to add a French drain. If you did go that route, the saturation of water in that area would never make iot to the wall to the degree that you may think. The French drains that I built where graded to daylight, lined with a continuous piece of heavy gage plastic, so any water entering would not get to the wall, it could only go where the slope dictated it to go.

If you case it is only water migrating back to the wall from a backwards grade due to settling, and the grade of the patio is sloped enough to rid the area of enough water so none stands in any area for a time, then raising the sunk pavers is all you would need.

All that said, the biggest issue you will face is reinstallation. Cleaning the pavers will be crucial. If the pavers do not go in as tight as they did before, well, you will not like it. Making sure all goes in as tight as possible is important. Another precaution, IMO, and in my experience make the area you remove 2 ft. bigger than you need, it will help trying not to crowd the work space. Use plywood or wide 2X material at the edges to keep from dislodging the pavers you wish to keep in place.

If your 3D drawing is really accurate in detail and the pavers are laid as you have drawn, you would do well to start pulling the pavers up at corner 4, removing them diagonally so that you remove them back towards corner 1 and 3. If you added enough sand to raise corner 4 level with corner 1, essentially making a level line where the patio meets the house on the long wall. This depends of course if the grade beyond will support the pavers being raised at all. If it does, this will help insure that there is plenty of fall without changing everything. Also if the pavers don't quite run as tight as the original setting, it is just an adjustment of the edge. A simpler fix than cutting pavers.

Last note, I have only used special sand in the joints, not as the setting bed. I call it special sand because I have not used polymeric sand. I have used a bone dry mix of masonry cement and fine sand, broomed in and tamped over the faces of the pavers. Broomed in again and watered. The paver surfaces must be absolutely dry to make this work and only after all visible traces of the sand mix is gone, is it watered.

Polymeric sand is a simpler process, but this was done way before I knew about that stuff.

  • Thanks Jack! The water comes exclusively off the patio. The patio diagram does not show the slopes (I am going to add that soon) but it is accurate to a 1/4"! My biggest fear is that I will not be able to redo the patio to the way it looks right now, otherwise I would proceed to removing the pavers, the sand, the gravel, I would fix the subgrade slope if it needs that and put everything back. I am thinking of a non invasive method to check if the subgrade settled or the settling is just at gravel/sand level.
    – MiniMe
    Oct 29, 2014 at 10:40
  • I would first remove the pavers. After that I would take a thin metal rod and eventually using a hammer, I will stick that into the sub-layers down to the point when I feel that it reached the sub-grade soil. At that point I will put a mark on the rod so I can have a reference and after that I will move the rod and measure the depth in various points for the affected area. Then I am going to know if the sub-grade is affected. I am not sure 100% about the precision of this method, I have never seen a compacted layer of gravel to see if it is easy to get the rod through.
    – MiniMe
    Oct 29, 2014 at 10:53
  • Here is what the pavers look like: diy.stackexchange.com/questions/51757/… I am not sure how the joints were done.Looks like special sand was used between pavers and that was topped with polymeric sand like in this picture pavingexpert.com/images/mortar/geojoint.gif (see the 9mm gap case) I am saying that because if you use a scrapper to remove the rubber like stuff that is still between pavers at the top you are left with gaps like in my second picture in the above quoted question. So it might be special sand + polymeric sand.Tricky
    – MiniMe
    Oct 29, 2014 at 10:59
  • Not really too tricky, if what you are scraping is the sand and not just grime of a sort that builds up over the years. I know of polymeric sand, but have had no practical experience with it. What I do know that sanded joints will get a crud built on top of it that can be "different:, perhaps like you refer to. I picture polymeric sand acting crumbly when given a reason to, not rubbery at all, but that may just be my ignorance speaking on the matter. Is the pattern herringbone? the picture does not quite give enough brick to say for sure what style it is laid. It is not running bond for sure.
    – Jack
    Oct 29, 2014 at 22:04
  • No it is not running bond, it is not fishbone. I forgot what it is called but I think there one more name left. I think that I need to speak with someone who knows how to properly size a drain. I think that one size that fits all is not OK. All I could find on internet was 4" pipe and gravel around it with various sizes for the trench. The reality is that that patio does not collects lots of water but rather a modes amount but in the wrong place: next to the wall. A properly sized drain should fix this. On top of that I need to find details about where to put the drain
    – MiniMe
    Oct 30, 2014 at 4:02

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