Hi. I have read some previous threads about this topic. I am planning to build a raised patio with concrete pavers on top of a small retaining wall (approx 12-14 inches high). I have NOT done this before, but I have done some reading, and have many questions. I apologize to the poor soul who reads this all the way through.

1) The manufacturer of the pavers I will be using recommended to roto-till dry portland cement mix into the soil to provide a stable base (recommended for sandy soils, which I have). Someone at a rock yard said this is not a good idea. Any other opinions?

2) I will need to fill in the area inside the retaining wall. Someone told me I can just use sand. Yes or no? If not, what should I use? If sand, does it need to be vibrated or compacted in before I continue?

3) Many sources recommend a 4-6 inch layer of crushed rock or composite base material, then a 1 inch layer of sand. Again, someone told me that 4-6 inches is not needed. Opinions? Also, I have read various descriptions of what this base material should be like. A nearby supplier sells granite screening (southeastern US region). Is this the stuff? How about crushed gravel? Also, how many tons of this stuff do I need for a 10 ft x 10 ft area? The wall will be 12-14" high and border 2 of the 10ft sides of the square.

4) Many retaining wall stones I have found have a ridge to help align them correctly, and have a trapezoidal shape. How do you make a 90 degree corner with these trapezoidal blocks? If I use rectangular stones without the ridge along the back edge, do I offset each stone slightly? How much?

5) I think I need to do the wall first, then fill the inside area and screed and level, then lay down the pavers. Is this correct? Also, is it best to try to fit the pavers flush within the borders of the wall, or lay the pavers along the top edge of the wall and use adhesive to keep them in place?

6) Some reading material recommends a slight slope away from the house for water runnoff. How do I slope the patio slightly without screwing up the retaining wall? Everything says that keeping the wall level is essential.

7) I have heard of paver sand and polymeric sand and joining sand and setting sand. ??? Needed or not? How much? Where is it available?

8) I have looked at home centers for pavers. Are landscape suppliers likely to have a better selection and/or prices?

9) Do I really need to rent that plate compactor to get the job done right?

10) I just have dirt now, but I thought about getting a small amount of sod to border the retaining wall and help hold in the soil. Good idea or no?


That's all I have for now. I'm sure I will think of more questions. I have become obsessed with this project, and it hasn't really begun yet. Thanks to those who can answer some or all of these questions.

 

#3 sounds more like the way it's done here. (N.C.)
# 9 is a must in any installation.

 

The first thing I would do is re-think the idea of the pavers sitting on the retaining wall. I think installing the wall with a solid cap unit and setting the pavers inside would be better. Since it is a low wall, a railing is not necessary, but a warning by a solid wall cap (attached with silicone adhesive) unit slightly above the patio would be a great safety feature. Also, if there is any settlement of you fill for the pavers, you would have a problem where part of the patio was on the wall and the rest is on the fill. This concept also eliminates the conflict between building the wall level and sloping the pavers slightly.

Regarding your othe questions -

1. Most of the majot retaining wall systems do not recommend any concrete under the walls, especially for high walls. Since yours is low, you might get away with it. All of the common, major systems have great sites of ideas and installation methods for each particular unit. Check the Allan Block, Anchor Wall Systems, Keystone and Versalok sites.

2 & 3. The fill below your paver patio should be well compacted to eliminate any long term settlement. Sand does not compact, it just looks like it when it is damp. Makes sure you ahve at least a 6" to 8" layer of compacted road base (different names in different places), which is the same stuff they put under an asphalt drive way. This should be compacted and be parallel to the slope you have chosen for the patio drainage. Place a 1" layer of concrete sand (uncompacted) on the base and screed it off so it has a uniform thickness and is parallel to the finished patio surface.

4. All of the sites for the good wall systems have good details for the installation and construction of corners and curved walls. You may have to split a retaining wall unit with a hammer and chisel for some details. Most units have a raised section for alighnment and shear strength. In some systems the first layer of units are turned ovr.

5. The wall is built first and then the area is backfilled. Whether you fit the pavers to the wall configuration or choose to cut/split, will depend on the shape of the paver and the pattern you lay them in.

6. You should slope the pavers away from the the house very slightly to prevent an accumulation of water around your foundation. - Just as you slope your yard away.

7. You should use a concrete sand as your 1" setting bed. Do not compact until after all pavers are laid. You can use a fine concrete sand or a masons sand for vibrating into the surface. Both are usually available in bags for a small patio. Polymeric sand is usually not justified or required, even on heavy duty or high-end paving jobs.

8. You can buy good pavers at big boxes and also get bad pavers. On minor chain makes their own and gladly replace them when they fail. Try to find an interlocking paver that is made by a national manufacturer or one that makes pavers meeting the ASTM standards that are required for municipal applications.

9. You will need a plate compactor for both the fill and the paver installation. You can rent one at many big boxes, lanscape dealers or rental companies. Go to the Interlocking Concrete Paving Institute (ICPI) site at icp.org for installation information.

10. The installation instuctions for your retaining wall units will provide the suggestions on the depth into the ground for the first layer. Usually it is a 1/2 or a full unit deep.

Good luck!!

Dick

 

Thanks for all the info. When I fill in, should it be entirely road base, or use some dirt to fill in the empty area below the base layer?

 

"Dirt" is not really a descrptive term and could mean many different things to different people living in different place.

If it have organics in it (black dirt) or a lot of clay, it will settle and eventhing above will settle.

Whatever you put in should be compacted to eliminate settlement.

Dick