Mini retaining wall...am I overthinking the design?

[TechieTechie]

Okay, so if you recall, crazy Techie used her highly recommended Burke bar to pop up (well, with help) 20k lbs of sandstone for a new to me patio.

Now that the patio is in, I finally convinced my landscaper that we need to fill the low portion of my yard, and in order to do that, I need a mini retaining wall around the patio at least a foot high, probably closer to 16". I know, it might not be fair to call it a retaining wall, but I'm calling it a retaining wall.

Because of the age of the house, I think dry laid standstone would look great. I am zone 6 and clay soil, so it does need to be sturdy. The question is, how sturdy?

I've found the drystack stone association sites (e.g. DSC) ...and for retaining walls, they recommend a 2 layer method (see pic).

But, my question is, for such a low wall, is this really necessary?

I don't think my current landscaper does a crapton of hardscaping, so I'm asking for others POVs. I'm all for overbuilding, but I don't want to pay for 2x the wall if I don't actually need it.

Thanks

 

[CraigStu]

My thought would be as sturdy as you think and maybe a little more. I see so many walls leaning the wrong way, and I always think, well I bet it looked good for the first few years but now it needs to be replaced. Not fun.

 

[kwb]

I would be inclined to do a poured wall and veneer it to give the appearance you are going for.

My go-to for small walls like this is split face block, start at least 1 full block below grade dry stacked, drive vertical rebar into earth a couple feet below the bottom course and fill the cores of the block. This method has worked well because it is easy to work on in whatever pace you have time (or budget) for, don't have to teach myself how to do mortar and tooling of joints, and have held up well everywhere I have put them. Think the tallest I have anywhere exposes 3 courses (24").

The only failure I have had is with the capstones where the amazon guy backed over part of one at the end of the driveway.

 

[larry_g]

When I was faced with this problem I went with a poured retaining wall with a wide cap for sitting on, as you can see in the picture. The mason used colored concrete and then textured it. It has worked well for us with large parties it provides lots of sitting room. We have since bought cushions that make things a bit more comfortable.

lg
no neat sig line

 

[Fixr]

Okay, so if you recall, crazy Techie used her highly recommended Burke bar to pop up (well, with help) 20k lbs of sandstone for a new to me patio.

Now that the patio is in, I finally convinced my landscaper that we need to fill the low portion of my yard, and in order to do that, I need a mini retaining wall around the patio at least a foot high, probably closer to 16". I know, it might not be fair to call it a retaining wall, but I'm calling it a retaining wall.

Because of the age of the house, I think dry laid standstone would look great. I am zone 6 and clay soil, so it does need to be sturdy. The question is, how sturdy?

I've found the drystack stone association sites (e.g. DSC) ...and for retaining walls, they recommend a 2 layer method (see pic).

But, my question is, for such a low wall, is this really necessary?

I don't think my current landscaper does a crapton of hardscaping, so I'm asking for others POVs. I'm all for overbuilding, but I don't want to pay for 2x the wall if I don't actually need it.

Thanks

My father-in-law and I built a highly rustic dry-laid stone wall 3-4 feet tall holding back a considerable slope of clay soil above it. It worked great for about 12 years until my wife & I decided to excavate out more flat space and ripped it out. We used limestone rocks that were previously excavated on the property. The main construction details amounted to: Use the biggest flattish rocks we could lift for the bulk of the wall, using smaller rocks to fill gaps; and lean the wall seriously into the slope. I see way too many nearly vertical stone retaining walls that fail way sooner than a retaining wall should.

The ground will get wet and extremely heavy, clay will swell, and the soil will always migrate downhill because gravity never sleeps. Using big rocks helped the wall stay together against soil movement, and starting with the wall seriously laid back against the slope gave more time before the soil movement would push the whole thing over.

I've seen lots of big poured concrete retaining walls with massive footers leaning the wrong way because people WAY underestimate the forces involved, especially when there was inadequate drainage.

All that said, as long as the wall is leaky and leans into the bank somewhat, you'll probably be fine with a single layer. And if it gets damaged, just restack the rocks.

 

[Lynden]

You are correct, your 12" to 16" high wall is a garden wall not a retaining wall. There will never be enough hydrostatic pressure behind the wall to cause it to tip or move. Build it for looks. I also like dry-laid sandstone walls and live in an area with an abundant supply of sandstone and many talented stone masons.

garden wall vs retaining wall

santa barbara sandstone walls

 

[theoldwizard1]

You are correct, your 12" to 16" high wall is a garden wall not a retaining wall. There will never be enough hydrostatic pressure behind the wall to cause it to tip or move.

No, but the freeze/thaw cycle in the Midwest will make it move ! This why all "man made" (concrete) garden wall blocks have a lip on the bottom. Each row in inset from the lower row so the lip locks it in place.

Dry stack look good, but in OH you need something much stronger behind it !

 

[TechieTechie]

Thanks all. I've had a couple dry stack specialists come out. They are both of the opinion that as long as we follow the appropriate 'good building' techniques (a good gravel base, a thick and buried first course, stones placed 'long side in', staggered joints, backsloped courses and crushed stone backfill), that will be fine for such a low wall....and will withstand our freeze/thaw cycles just fine.

Thanks for giving me food for thought.

 

[jfleisher]

I did a low retaining wall on my house a few years ago, laid the blocks dry.

 

[theoldwizard1]

Thanks all. I've had a couple dry stack specialists come out. They are both of the opinion that as long as we follow the appropriate 'good building' techniques (a good gravel base, a thick and buried first course, stones placed 'long side in', staggered joints, backsloped courses and crushed stone backfill), that will be fine for such a low wall....and will withstand our freeze/thaw cycles just fine.

I would only add that you need to lay down land scape fabric against the uphill side and the base BEFORE adding crushed stone (3/4" crushed limestone is the best . Make sure the base is "deep enough" (?) and compacted.

Drainage of the base and the back fill is KEY !

 

[theoldwizard1]

I did a low retaining wall on my house a few years ago, laid the blocks dry.

Yes, but those blocks have a lip on the bottom that locks them into the course below.

 

[roc_on_the_rocks]

I did a low retaining wall on my house a few years ago, laid the blocks dry.

It looks great. I have a need to build a similarly sized 'retaining wall', starting at that height and tapering off to zero.

What do you mean by 'laid the blocks dry'?

Does such a short 'retaining wall' still need a base of gravel and/or sand?

I plan using the blocks with the lip on the bottom that locks them into the course below.

 

[TechieTechie]

Wizard is referring to manufactured stone 'lip on the bottom'.

I'm using actual stone...each piece weighs 10-100 lbs, depending upon the size. Whole other level of strength/structural integrity.

@roc_on_the_rocks, base really comes down to your soil and condition and if you are using manufactured or natural stone. My yard is heavy clay, boggy and even digging down 6-8 inches, I may not get to previously undisturbed earth (because I had to dig out an old wooden deck). And, I'm using natural stone. BTCV (British stone trust) and the old school methods (e.g. McRaven) for dry stack versus newer US based methods are split, 50/50 about gravel versus undisturbed compacted soil base. I don't need geogrid because I'm heavy clay, I don't have to worry much about silting.

If you are using manufactured stone absolutely gravel base, no doubt (because these walls are not nearly as strong/heavy as natural stone and need the additional drainage to ensure structural integrity). Doubly so for sandy soils.

Approach is very different for natural stone versus manufactured. And the term 'dry stack' was traditionally used in relation to natural stone laid w/o mortar. But now is also used to refer to manufactured stone install without mortar. Make sure you are getting the right advice for the job and materials YOU intend to use.

 

[roc_on_the_rocks]

Wizard is referring to manufactured stone 'lip on the bottom'.

I'm using actual stone...each piece weighs 10-100 lbs, depending upon the size. Whole other level of strength/structural integrity.

@roc_on_the_rocks, base really comes down to your soil and condition and if you are using manufactured or natural stone. My yard is heavy clay, boggy and even digging down 6-8 inches, I may not get to previously undisturbed earth (because I had to dig out an old wooden deck). And, I'm using natural stone. BTCV (British stone trust) and the old school methods (e.g. McRaven) for dry stack versus newer US based methods are split, 50/50 about gravel versus undisturbed compacted soil base. I don't need geogrid because I'm heavy clay, I don't have to worry much about silting.

If you are using manufactured stone absolutely gravel base, no doubt (because these walls are not nearly as strong/heavy as natural stone and need the additional drainage to ensure structural integrity). Doubly so for sandy soils.

Approach is very different for natural stone versus manufactured. And the term 'dry stack' was traditionally used in relation to natural stone laid w/o mortar. But now is also used to refer to manufactured stone install without mortar. Make sure you are getting the right advice for the job and materials YOU intend to use.

@TechieTechie, thank you so much for the great information.

My 'retaining wall' would be less then 30-foot long, with a height varying from zero to up to 3 courses of these manufactured blocks from Lowe's (they do have the 'lip' behind):

• Oldcastle 4-in H x 11.5-in L x 8-in D Tan Concrete Retaining Wall Block - Item #104157 • Model #110602211
• 4-in H x 11.5-in L x 8-in D Red/Charcoal Concrete Retaining Wall Block - Item #104158 • Model #110602335

Given how short my 'wall' is, should a 4-inch layer of paver base (like this) be sufficient? Solid clay soil here.

Lastly, would gluing blocks with LOCTITE PL 500 Landscape Block Off-white Solvent Exterior Construction Adhesive contribute to the wall strength/longevity?

Thanks a lot.

OP, sorry for hijacking the thread, hopefully these questions overlap with yours, or help others.

 

[andyvh1959]

Back in Sept 2022 I built a 50' long retaining wall along my driveway to add some width and to meet up with the front of my shop I built in 2021. Up here in Wisconsin have to consider frost heave and how it moves a retaining wall if not laid properly, like many do around here. Within two winters the hastily set up walls are pushed out of shape.

For mine I had dug a trench more than 12" wide, and at least six inches deeper than the base row of block. I planned the digging to allow at min six inches of gravel fill behind the block rows. I then filled in six inches of packed/screeded/leveled gravel for the base row of block. I used a string set level over the entire run, so I could use a reference stick to set the base level for the first row of block. Then I started laying the base row and next row about ten feet long, then went back and laid the next two rows, then back to the base for another ten feet of run. As I laid the third and fourth row I backfilled with gravel I packed down behind the block. I didn't want soil right against the back of the block, so the gravel allows water to drain down behind the block. Once I got near the top row I backfilled with soil and glued down the cap stones.

After I finished the wall I planted ground covers, small pine trees I transplanted and tulips. Come next May it looked like the pic shows. Been through two winter cycles now and all looks good. I did similar block walls around lamp posts out by the driveway back in 2004, still solid and level to this day. Neighbor guy laid two row of the same block around plantings in his front yard, set them on the dirt and backfilled with dirt. Within two winters they're all pushed out and toppled over. My now-ex at the time I laid the walls back in 2004 asked me why it took me so long to set simple block walls (like over a long weekend) when the naighbor did his in an afternoon. Hmmm?

 

[rayra]

It looks great. I have a need to build a similarly sized 'retaining wall', starting at that height and tapering off to zero.

What do you mean by 'laid the blocks dry'?

Does such a short 'retaining wall' still need a base of gravel and/or sand?

I plan using the blocks with the lip on the bottom that locks them into the course below.

Dry stacking usually means no mortar / grout or bonding adhesives.

 

[theoldwizard1]

@TechieTechie, thank you so much for the great information.

My 'retaining wall' would be less then 30-foot long, with a height varying from zero to up to 3 courses of these manufactured blocks from Lowe's (they do have the 'lip' behind):

• Oldcastle 4-in H x 11.5-in L x 8-in D Tan Concrete Retaining Wall Block - Item #104157 • Model #110602211
• 4-in H x 11.5-in L x 8-in D Red/Charcoal Concrete Retaining Wall Block - Item #104158 • Model #110602335

Given how short my 'wall' is, should a 4-inch layer of paver base (like this) be sufficient? Solid clay soil here.

The short answer is NO !

I had a 1 block high "wall" just to demark the flower bed from the lawn. It had a 4"-6" finely crushed base (we call it "slag" around here). It lasted a couple of years before it got moved up and down by frost.

I bit the bullet last year and I paid a guy to remove all the blocks, dig down deep enough to put 4" of new slag and set the first row of blocks even with the grass. Second block was just laid on top, so the whole thing came out the original height. Mostly clay, with a couple inches of top soil. No movement this past winter !