drystone retaining wall versus mortared
tjem
| Posted in Construction Techniques on
I am building a patio with retaining wall here in south west Connecticut. The exposed side of the wall is going to be no more than 28 inches high and there is a good long hill rising up on the other side of it. I have excavated to 17 inches below grade for both the retaining wall and patio. My base material is tamped processed rock. I would like to avoid concrete and do a drystone wall with a bluestone cap mortared on top. Is this going to work or is a concrete footing and semi-mortared wall the best way to resist frost heave problems in the winter?
thanks for any advise.
TJEM
Replies
Yes frost heave will ruin the bluestone cap! Either dry stack it completely or cement it with footings going below frost line.
I'd dig deeper (below the frost line) but unless you have
a wet spot to deal with 28" is not that big of a deal.
A footer is always better of course, but a well laid wall should
last a very long time.
Not sure what Frenchy is worried about but the cap will be fine IMHO.
Henley,
Frost heaves do not lift all areas of a wall the same amount.. if the wall is dry stacked and the bluestone cemented to loose stone.. it will remian fine untill the frost heaves shove the wall up.
If it's properly dry stacked the wall will remain solid for a very long time but the cap stone will break loose. Now if you can safely dry stack the blue stone cap on top the wall should be fine..
Ah, I missed "the mortared on top" part. yup, if your gonna let it move, let it move.
Dry stack wall should be just fine. Just make sure there is lots of free draining rock behind the wall so that water does not stay behind or below the wall. Is your existing soil under and around the wall a free draining sandy soil or is it heavy clay? If you have very free draining soil you will likely see little frost action. As far as the bluestone cap, yes it is quite possible/probable that the mortared cap would come loose in places with frost action. You could always try to stick it back on using the flexible adhesive used for attaching the cap stones on precast walls. It is not the ideal scenario .... by combining a mortared cap onto a "flexible" dry stack wall you are combining something that is intended to be fixed with something intended to have some give, so it may require ongoing attention. If you still plan on trying this method at least try to get large cap stones so that the mass of the stone itself atop a nicely built top course of stone creates stability of it's own, and does not rely on the mortar so much.
Building a mortared wall will require even more attention to ensuring that water drains freely away from around the wall.
Ditto what the others have said- drainage being key. In setting the bluestone caps, I always butter the back with straight portland and water,then set on your mud. Seems to cut out the stones popping loose down the road. Also when working on a flexible base(stone vs crete) I usually just butt the caps instead of pointing.
Steve