The terraces can move for different reasons, but mainly due to the freeze or thaw cycles. This is why it is recommended to bury the base at more than 4 or 5 feet. Thus, the gel will not affect the drumsticks. This step can be done by you rather easily. The best website for the same is there.
- Dig with a shovel or using a mechanical gas auger can be rented
- Place a cardboard sono-tube at the bottom of the hole
- Mix the concrete preferably with Portland GUL cement or with cement additions
Warning: Clay tends to expand and shrink depending on its moisture content. If you build on soil that has a high content, the terrace could be affected by heavy rain and long periods of drought.
If you come across a bed of bedrock, it’s a good thing. Beware: a large pebble is not necessarily a bed of substrate, although if you hit it and it seems really very solid, the bottom of it is probably below the frost line, in which case you can erect the terrace using it as a base.
The piles are screwed into the ground, still below the frost line, and serve as a structure. Effective for building a terrace, you just have to make sure they are level. They are available in any large-scale home improvement store and they normally have a hole that allows the use of a 2×4 as a lever.
Be careful, however: as they are not as wide as the sonotubes, the room for maneuver is more limited. If your soil is very rocky, it is best to call a professional, who will install it, under $ 200 of the pile, in most regions.
Deck blocks or elephant legs
Instead of being driven under the frost line, the structure here is floating, deposited directly on the ground. It is a simpler and less expensive way to build the terrace, but it can be more demanding to keep everything perfectly level, and it could require more maintenance over time, the risk of compaction being high.
For more durability, the blocks can be insulated against frost. Just put a rigid panel under the terrace and around the foundations and cover everything with crushed stones. For more durability, it is better to put sonotubes or piles screwed below the level of the gel.
Choose your wood
Treated wood is today less toxic than it has already been, but its environmental impact is still less benign than that of natural wood. Its treatment does not penetrate deep into the wood and the cut ends leave an unprotected surface. It is preferable to use products among the following, both for the environmental impact and for the lifetime.
Cedar and hemlock
Cedar is by far the most common untreated material. It usually comes in 1.25 “thick planks. It can be left raw, but light coloring will increase its durability while reducing its chances of turning gray under UV exposure.
Red cedar has natural anti-rotting characteristics, but its price is high. It is preferable to opt for planed white cedar, available in specialized sawmills. Cedar, on the other hand, is not ideal for structure. Hemlock is a better choice: it is a very strong and very durable wood when protected from moisture. This type of terrace, a mixture of cedar and hemlock, could last more than 20 years if it is well maintained.