Life in an old Japanese house Vol.12: Japanese homes and stone walls

Japan is a country of hills and mountains where various methods have always been employed to utilize land such as making flat land for homes by building into the mountainside and raising the land near sea level to prevent flooding. When land is utilized in this way, a stone retaining wall constructed by piling up stones is often built. Although nowadays concrete retaining walls are the norm and newly built stone walls are uncommon, there are still plenty of places you’ll still find old stone walls. Many living in old homes find themselves having to perform upkeep and maintenance on their stone walls.

Just as times and culture have changed, many people are unaware of proper stonewall maintenance causing more and more stonewalls to be at risk of collapse. With climate change causing more frequent occurrences of heavy rainfall in recent years, quick action needs to be taken to maintain them.

Regardless of whether homes are in potential landslide zones or not, when homes are built upon stone walls or have stone walls behind them there is a risk of walls collapsing causing stones or earth to pour out onto homes.

Though there is plenty of information on home DIY nowadays, there is a severe shortage of information on stone wall maintenance.

A stone wall is composed of large stones stacked in front with pebbles packed behind them and finally natural earth behind them.  Each of the stones in the wall is pivotal to its construction so even the small stones wedged in between larger ones can not ever be removed. With a stone removed, the wall begins to hollow out which can allow pebbles or sand to start to come out which in turn weakens the whole wall.

It has long been said that a stone wall with weeds growing in it is a weak wall. If weeds are growing then either there is a build-up of dirt in the gaps or there are not enough pebbles in the back. If a tree is living in the edges or gaps of a wall then you should be careful that the root does not begin to push against the wall since that will also cause it to break.

雑草の生えた石垣

When dealing with weeds in your wall, you should resist the urge to pull out the whole weed since that will also cause hollowing out of your wall. Instead, just trim the exposed part of the weed. I’ve heard that walls have even collapsed after using herbicide on them. Once sprayed and the weed and root had wilted, this caused earth from within the wall to pour out. Should you decide to pull out the root of the weed or spray your wall then you should plug the wall with cement mortar immediately afterward.

A wall that is said to be swollen or bulging will surely break at some point, so it should be reinforced with mortar from within or the wall itself needs to be reset. In this case, it is common to call in a specialist or contractor to handle the job. The most common method of repair employed by professionals nowadays is to insert a mixture of mortar and adhesive between the gaps.

If the wall still doesn’t have many gaps or hollow spots, then you can hire someone to cover the wall with cement which would help stop pebbles and sand from coming out.

In reality, though, hiring a professional can cost thousands or tens of thousands of dollars in repair so it is not that easy to do. Some local governments may provide subsidies to assist with the repair but when it isn’t available many turn to doing it themselves. For walls that are in a progressed state of hollowing out, it will be hard to repair entirely on your own so you should consult a professional before trying DIY. If the wall is still in not so bad a state, then you should be able to cover the wall with mortar yourself by purchasing a squeezable bag to pour in the mortar (think of the kind used for putting on icing). That said, with no place for water to escape a fully covered wall is also not safe so it is necessary to have drains placed throughout the wall. When rainwater builds up inside the wall, pressure also builds and without sufficient drains, the wall could burst. If you consider installing the drains yourself, they must be properly installed so you should also consult a professional for advice while doing this.

Stone walls can break not just from heavy rains or earthquakes, but also from leaks in water or drain water pipes.  Also, vibrations from nearby roads or railroad tracks are known to cause stone walls from within to hollow out. Therefore it is crucial to maintain not just the stone wall but everything in the vicinity of your home.

A water drain was found in a concrete block retaining wall. 
Cleaning the debris in the pipes is also important maintenance.

A stone wall was repaired by covering it with mortar and water drains.

Drainage holes are made of bamboo instead of pipes.

A stone wall was repaired by covering it with mortar without a water drain.

This is a stone wall of Kochi Castle built with a method called Nozura-zumi.Although it looks like a messy pile with lots of gaps. Nozura-zumi is often used in areas where there is a lot of rainfall, where it drains water well and is less likely to collapse, and Nozura-zumi stone walls often do not need drainage holes or mortar to fill the joints.

One final issue with stone wall maintenance is the issue of whose responsibility it is. If stone walls fall clearly within someone's property lines it would be no issue, but in fact, it is common for it to be unknown who the property owner is or where the property lines are. In this case, it is possible to consult the legal affairs bureau and find out the boundary of the property or the name it is registered to, but since they can not release their contact information, some homeowners are stuck not being able to get consent to have the wall repaired. If you find yourself stuck living next to a neighbor's wall at risk of breaking and find yourself unable to contact the owner then first you should contact your local government. At the same time, you should also keep in mind to maintain your walls so you cause no damage to homes below you.