About 7 years ago I laid a flagstone patio in my backyard. I compacted the ground, laid a layer of about 3 inches of sand, then laid my stone. Between the stone I spread some red crushed gravel that was supposed to hold the stones in place. For the first year or so it looked great.

But the soil is clay and any sand or gravel spread out on it disappears into the soil after about 18 months. For the first two years I spread more gravel each spring as the ground between the stones seemed to shrink away - the stones seem to set about a half inch above the ground. For 3 years we tried planting moss between the stones but that never took hold.

I am wondering if grouting the areas between the stones would not hold them better in place and give a more level and even appearance. Any disadvanted to grouting at this late date? Any alternatives?

Thank you.

 

I do not know of anything "easy" you can apply on top at this point to make maintenance easier. Polymeric sand might offer some benefit but with your base and the previous joint materials I don't know if it has much chance of succeeding.

Building, road, retaining wall or patio it's success and longevity depends on the foundation. Unfortunately it's work that's not pretty and not seen in the finished product so it's often one of the corners cut in DIY projects. Without the proper base your patio is susceptible to heave and movement during freeze/thaw and dry/wet cycles. No grouting or surface treatment that I know of can compensate or prevent it. You can deal with the movement your seeing and dress the joints every season or bite the bullet and go for a more permenant solution.

 

I've never heard of sand or gravel disappearing when absorbed by underlying clay. As most clays are somewhat impervious, it's more likely that your sand/gravel are washing away during the heavy rains your property experiences in Oregon (if similar to the rains in my part of Oregon). Also, the sand layer you used for a base may also be contributing to the problem, as most sands don't compact well enough to form a stable base.

 

you're got patio stones that walk ? usually their weight keeps them in their place,,, if that doesn't work well, try scolding 'em in a loud voice we have the same trouble w/pine straw mulch in atl,,, about 2mos after we put it down, someone sneaks in & lifts it

if you're talking about the stone staying level, you'll need better drainage, base, & less expansive soil [ that suggests a complete tearout & re-build ] OR a frost-free climate,,, you post'd compaction THEN 3" sand,,, did you compact a new granular base OR existing topsoil ?

 

I think Staydry is correct. Also you said you laid sand then stone. That sounds backwards to me. Normally you lay stone as a base then sand as a leveling medium to keep the stone slabs in place.