Should I add sand or more limestone crush to raise a patio with no gravel bedding?

Question

I need to regrade my patio and I had a quick look under the pavers to see how it was built. To my surprise I found the following layers:

• one thin layer off gravel -you would say it is about 1/4in thin
• weed barrier
• 4" crushed limestone
• precast brick pavers

I expected something more like 4" of gravel and 1" of sand + pavers on top (like it is described here : http://www.homedepot.ca/know-how/projects0/laying-out-and-digging-a-patio )

I think that the whole thing is too little permeable to water, and it drains more difficultly and that correlated with a slope toward the house is giving me a wet wall ... I need to raise the level of the patio with 1"-2" in order to make it drain away of the house

Now the question is: do I add sand over the existing limestone crush or I buy more limestone crush ?

From drainage perspective, is it normal to have mostly just this limestone crash layer and nothing else? Will this crushed limestone trap the water longer than it should?

Answer 1

I wouldn't call that a typical base, but if it was properly compacted, it should work. The typical base is pretty much what you described:

• topsoil dug down to undisturbed soil and/or topsoil dug out then soil machine compacted
• 2" layer of crushed rock, machine compacted
• 2" another layer of crushed rock, machine compacted
• repeat until you get to 4" or the desired height (if above 4")
• 1" sand, leveled
• pavers

Note that in this system, you're not designing for permeability or drainage at all. If you are using pavers, this is hardscaping, and is meant to shed water, not absorb it. To properly shed, it needs to be properly sloped. This is true for the base layer as well.

The purpose of the base layer is to create a solid, stable surface. Ability to drain is desirable (to avoid frost heave) but that's secondary to providing a proper surface to shed water.

In your case, it sounds like you already have 4" of compatible material. I'd do the following:

1. remove pavers
2. rent a compactor and compact existing base
3. add additional base material and compact to get the slope you want
4. add sand
5. put pavers back
6. add locking sand to joints

the big catch here is that this will ultimately raise your patio next to your house several inches. If that's tolerable, you're good to go. If not, then you have to do the reverse...instead of adding material closer to the house, you need to take material and remove it further away from the house. This will reduce your total base at the outside edges, though. That may be acceptable in your case.

Answer 2

OK, now this is what I would suggest you to do (and what has proven to be the best solution according to my experience): Of course first take everything out. Be careful when you remove bricks not to damage them, and where you put them. Remove everything up to last layer of gravel. Add more gravel so that total thickness of this layer is round 4 inches. When I say 4 inches I mean hardly compacted; that is also very important: you must compact this layer really good. My advice is to use specialized vibrating equipment. Now comes the part which you will most likely disagree but, once again, according to my experience it is the only long term solution: pour thin concrete slab (round 3 inches, maybe little more) and reinforce it with some thin mash. This creates rock solid layer for your bricks, and guarantees that it will stay flat, without any bumps or settling for a very long time. Next step would be to make fine sand bed. Its only purpose is to fill gaps between bricks and to make them stand vertical. Now you can put again your bricks and that's it. In case you want to fill in the gaps between bricks (fugues) you can fill them with extra fine sand, or with some mortar. I know this sounds complicated but for a rather small area like patio I would highly recommend that you do it this way. If you have any questions feel free to ask.