Six INCHES? No, you don't need mortar or a base, or at least you wouldn't in my climate (zone 8). If you do use a base, heed the advice of Botann, above. Or you can use sand, but again, use sharp sand, not the one with rounded particles. The question that determines whether or not to do a base has to do with what happens if you get frost heave or any sinkage. How difficult will it be to repair the wall and do you want to be bothered with that? Me, on such a small wall, I'd far rather have to do some spot repairs from time to time than mess with gravel and mortar to build it. But definitely, there are some great books out there on building with stone. Is this wall going to be a retaining wall, or free standing? KarinL

Hey Ken. Same state, same question! Mine will be about 15" h x 15' long and will be using stacking stone. Mind if I ask if you recall how deep you dug your trench the first time and how many inches of crushed stone you used. Did you also backfill with stone and if so, how deep and tall? Thanks and good luck!

If you've never constructed a stone retaining wall before, whether mortared or dry set, it doesn't matter..., an 8' tall dry set wall is not something you want to start off with. Even changing the design to 2 smaller offset walls carries with it the need for a little real engineering in order to understand the zones of influence of one wall's foundation & load upon the other, the load above the higher wall, the horizontal distance between the 2 walls, ground and surface (rain) water locally, the characteristics of the existing soils upon which the wall(s) may be founded, and last but not least, local or regional codes that may pertain to wall construction of given heights. Certainly, there are an inexperienced many who go forward with projects like this and many are successfully completed, but usually by chance and not design. Old rules of thumb, by which many of us (older folks) still work, tell that the base of the wall should be founded upon and supported by a compacted layer of gravel or crushed stone at least 6" thick, all on top of native soils which have been previously compacted (with all organic soils removed). They tell us that the width of the wall's base should be about 40% of the height of the wall, and the base should be buried at least 12" below adjacent grade. They also tell us that the visible face of the wall should batter back at least 3 (horizontal) to 12 (vertical)...the back of the wall in that case being nearly vertical...and that the top of the wall (capstone) should be 12"-18" wide. Along the way, 'through-stones' should be installed at certain intervals both horizontally and vertically. (Through-stones being those whose ends can be seen at both the face and back of the wall, thereby 'tying' both faces together.) And,with regard to drainage of groundwater from behind the wall, they tell us to remember that the wall is dry set, without mortar, possessing a myriad of spaces that can carry water from front to back without the need for mechanical devices such as pipes (drain tile) or weeps. The important thing is placing free-draining material (like gravel or crushed stone) behind the wall 6"-12" thick to allow the water to migrate easily to the spaces in the wall. Now, all of this should be viewed in the context of the type of stone being used. Rules of thumb are just that, nothing more, and shouldn't be considered engineering advice. Flat stones of nearly regular size and shape are fairly easy to work with. 'Found fieldstone', if anything like the native fieldstone found here in New England, is extremely irregular, tending more to the 'rounded' than the 'flat', and can be very difficult and time consuming to work with. It's not at all impossible, but best done by someone with experience. At the very least, almost each and every stone placement needs to be carefully thought out, reviewed, and reviewed again. All of this being said, 'tis your project and your effort, so at the least, plan on it taking 4 times as long as you initially thought, making patience, care, and safety utmost in the course of events.

Don't know where you can get the foam, but I have some questions you might want to ask yourself. I am sure you have thought about most of them, but you may have missed a few: 1. Was that TV show in a place that freezes? What happens to the foam exposed to the elements? Would it be better to use a landscaping adhesive made for that application that would surely last? 2. Does it carry any toxic compounds for the soil or worse, for the pond? 3. Do I really want that foam displacing soil that plants could grow in? (I suspect for most gardeners, It wouldn't matter, but it would be disastrous for an alpine garden.) 4. If used in a wall: does it matter that foam would impede water flow through the wall? 5. Can I remove the foam if it gets on the face of rocks? It seems like such an easy fix, but I'm sure you can tell I am skeptical. Good Luck!