Losing sand between my pavers

[dragoncar]

I've got a paver patio over a retaining wall and I keep losing the sand!  Here's the situation:

At some point, there was movement, as there are now fairly large gaps between some pavers.  However, the gravity block retaining wall shows no obvious signs of failure (it's only a few feet high)

I keep adding sand, and it seems like it's draining right out the bottom after a few weeks.  This appears to be accelerating!  I've tried lifting pavers and it seems they rest on a bed of compacted sand, so I don't know where it's going.  It's only in select locations... the vast majority of the patio looks brand new.

So what's happening?  I know pavers are typically on a sand course over a gravel course.  Is the sand sinking into the gravel because it wasn't properly compacted to begin with?  If I keep adding sand will it eventually fill the cracks?  I know I can use polymeric sand, but I feel like that will just hide the issue of losing sand out the bottom.

So... any tips?  Should I re-lay all the pavers to remove the gaps?  Should I rent a compactor and then use polymeric sand?  Sand isn't super expensive in bulk, but I feel like everytime I'm at home depot I pick up a $3 bag.

[deborah]

Do you have ants?

[dragoncar]

Do you have ants?

Not that I know of.  I saw a hole in the dirt next to the pavers a little while ago and thought maybe it was voles... but I don't have anything voles like to eat around the pavers.  The hole was maybe an inch across with no mound.  I ended up assuming whatever was sucking out my sand did the same thing at that hole (it was after a small earthquake so I figured ground settling was more expected at that time)

[deborah]

So you could have a crack in the ground where the earthquake was, rather than a poorly compacted base.

I suspect that the base was properly compacted because you have not said your pavers are not level.

[Beef Rindly]

Are you getting any subsidence/settling with the pavers?  I don't know how much rain you get, but if you have the grade too steep, rain will run more quickly off of the pagers than otherwise, which can contribute to erosion.  Polymeric sand is pretty nice I think - I didn't use it but my friends did.  Their pavers don't have grass growing in the cracks like mine do.  When the time comes for me to resand the joints - which is common - I will switch to polymeric sand. 

Good luck!

[dragoncar]

The pavers do seem to be pretty much level -- no subsidence or tilting.  Just the sand is disappearing.  It's not rain -- I'm in CA and we don't get any during the summer.  I doubt it's wind because it's only in certain areas, and pretty deep (up to like 1.5 inch trench of missing sand). 

I agree it could be an earthquake but those don't really cause "cracks in the ground".  We do have very clay soil around here, so when it gets dry in the summer the clay contracts and creates gaps (exaggerated example below).  Maybe that's the cause!



Maybe I'll get a real picture tomorrow.

[deborah]

Yes! It will be cracks in the clay. I hear it's been extremely dry in California. Don't worry, it will be wet soon enough - we are about to have an el nino, so we will have a drought later this year and you will have our rain. And this el nino is shaping up to be a big one. Unfortunately, by then your sand will all be amalgamated into the clay, so you still need to put some more sand between your pavers.

[Rezdent]

Yes! It will be cracks in the clay. I hear it's been extremely dry in California. Don't worry, it will be wet soon enough - we are about to have an el nino, so we will have a drought later this year and you will have our rain. And this el nino is shaping up to be a big one. Unfortunately, by then your sand will all be amalgamated into the clay, so you still need to put some more sand between your pavers.

Will adding sand now cause problems with heaving pavers once the clay starts expanding again?

[dragoncar]

Yes! It will be cracks in the clay. I hear it's been extremely dry in California. Don't worry, it will be wet soon enough - we are about to have an el nino, so we will have a drought later this year and you will have our rain. And this el nino is shaping up to be a big one. Unfortunately, by then your sand will all be amalgamated into the clay, so you still need to put some more sand between your pavers.

Will adding sand now cause problems with heaving pavers once the clay starts expanding again?

Seems like a possibility, but I'm not sure what else to do unless I lay landscaping fabric underneath the pavers to retain the sand!.... although as I mentioned this patio is next to a retaining wall so I suspect there must be some fill soil that might not be clay.

[sisto]

I think you have either ants or possibly termites, the ground kind. More likely ants though and yes they can wreak havoc. I like your idea of weed block under the pavers. You might not have to do that if you get the ants controlled though.

[dragoncar]

I think you have either ants or possibly termites, the ground kind. More likely ants though and yes they can wreak havoc. I like your idea of weed block under the pavers. You might not have to do that if you get the ants controlled though.

Interesting theory... I've never seen an ant and we had a teine inspection when we bought the place 9 mo ago.  How can i confirm?  Start pulling up more pavers?  Just spray an insecticide?

[deborah]

Get some of that sticky ant poison, put a bit on a paver, and see if the ants eat it (go back later and see if there is a ring of ants around it). I would suggest a teaspoon of honey or a similar amount of sugar water, but you may come back too late to see what has eaten it.

[Slam]

Municipal Civil Engineer here.  Look into sandlock joint sand.  It's like a glue that you mix with the sand.  You mix it together when it's dry and sweep it into the joints like normal, then spray it with water.  It does a pretty good job.  We have a lot of brick pavers in the downtown area and always use the stuff.  Saves us a pretty good amount on maintenance.

Edit for fine print: I am not registered in the state of California, I know nothing about your soil types or earthquakes.  If your subgrade was not originally well compacted, then yeah you need to fix that or you will have problems forever.

[James]

Are you sure the pavers are no longer moving? If the distance between the blocks is expanding then the sand will drop to the bottom. I assume not since that would be obvious after a while, but you did say there was movement at one point.

[dragoncar]

Are you sure the pavers are no longer moving? If the distance between the blocks is expanding then the sand will drop to the bottom. I assume not since that would be obvious after a while, but you did say there was movement at one point.

No, I'm not sure.  I seems like if they keep moving a few more inches, the retaining wall will collapse and I'll have bigger worries!  Don't know how much play there can really be with a gravity block retaining wall.

A family member just repacked all the cracks, using water and a tamper, and it looks much better than my "sweep sand into the cracks" approach so I guess we will see how long this lasts.  I did notice that a few blocks now seem raised -- maybe some of them were just shifting such that sand moved from the sides underneath the blocks.  But it's only a few blocks.  I also saw one ant!  Anyways, if (when) the sand disappears again, I'll post some photos and try some of the other suggestions here.

Also of note, there's a patio drain in the vicinity where the sand is disappearing.  Not sure how it's constructed, but I tend to imagine some sand might be washing into a perforated pipe and down the drain when I water nearby plants (but we really don't have any excess water in the summer here in CA)

[stachethis]

Assuming there were no issues with the construction of the patio, you probably want to look into polymeric sand.

I am dealing with a similar issue at my house. We moved into a new house last year with a relatively large paver patio. We had a ton of weeds sprout up this spring/summer due to copious rainfall. Removing the weeds removed a large amount of the sand in between the pavers and rather than replacing with regular sand, I decided to go polymeric route.

Polymeric sand is basically sand mixed with concrete. You apply like regular sand, wet (to activate the concrete) and wait to harden (usually in a day or so). The sand then locks in between the pavers.

Removing existing sand is a bitch - best way is using a pressure washer. Warning, this is a dirty, dirty job (both to yourself and surrounding area) but is easily doable. After pressure washing, let dry, then follow installation instructions for polymeric sand. I completed one portion of my patio and am really happy with results. You can get the stuff and bix box stores or landscaping company in different shades. Good luck.

[dragoncar]

My issue with polymeric sand is 1) it supposedly leaves a haze unless you are really meticulous at installing it and 2) it will keep the sand from sinking but that just hides whatever issue is underneath the sinking sand-- I don't want a giant sinkhole opening up in a couple years

[Slam]

My issue with polymeric sand is 1) it supposedly leaves a haze unless you are really meticulous at installing it and 2) it will keep the sand from sinking but that just hides whatever issue is underneath the sinking sand-- I don't want a giant sinkhole opening up in a couple years

I can assure you that polymeric sand is not strong enough to bridge over a giant sinkhole.

[Slam]

But then again, this might happen to you: https://www.youtube.com/watch?v=v5y4n-qsbpY