Building a garden against a brick wall can have some benefits as it saves space and also utilizes the beauty provided by the backdrop of the brick wall.
Protecting a brick wall from moisture can be done by placing a barrier to prevent moisture from ingression into the wall’s foundation as it is one of the main concerns with having soil close to a wall. Additionally, topsoil can be prevented from splashing onto brick walls by the use of mulches and fabric ground cover.
The main issue soil poses to a brick wall is moisture which has to be addressed to prevent damage to the house’s foundation.
If you are going to do gardening against a brick wall you should go for it, but there are some things you should know before you venture further to prevent moisture and other issues which may be caused by having soil next to a brick wall.
Protecting a Brick Wall from Soil
In many cases, the brick veneer can start a couple of feet above the ground where the foundation layer stops.
This is why in some buildings you will see a concrete layer before you see the brick. In other cases, the veneer layer can be constructed so that it reaches all the way down into the soil layer to completely cover the concrete foundation.
In older houses, veneers can extend down to the soil. However, this does not mean that the weep holes are blocked. The wall is constructed such that the weep holes are still present above the foundation layer.
You can place dirt against a brick wall only if there is protection against moisture in place so that the dirt does not affect the wall that it’s pressing against.
Moisture is the biggest cause of foundation failure, which is why it is imperative to ensure that any garden constructed close to a house is done such that water can drain away from the home.
There are many ways to protect a wall from moisture but I have found this Polyurethane Sheet from amazon to be the most cost-effective and durable in moisture prevention. You can find it by clicking here.
What Product Should You Use to Protect the Brick?
There are many different products out there that provide good benefits when it comes to preventing moisture from ingressing into concrete which can have devastating effects on a house’s foundation.
Materials Used to Prevent Moisture Ingress into the Foundation –
Polyurethane coating –
This coating is a synthetic coating and is usually two to three times thicker than normal coatings.
The purpose of the coating is to prevent moisture ingression from the outer walls into the inner parts where it can cause stresses and cracks over time.
The coating should be applied on a properly dried surface cleaned of any debris or dirt which can cause it to flake off afterward.
Concrete Penetrant –
Penetrating sealers work by increasing surface tension on the concrete.
These products will create hydrophobic water-shedding, meaning water will quickly be repelled from the sealed concrete surface instead of soaking in.
It reduces a substrate’s ability to absorb water or stains at the molecular level.
This coating should also be applied to a clean and dry surface.
Fiber Cement Board –
Fiber cement board is one of the better choices of building materials that work on home exteriors to prevent moisture from ingressing into the house’s foundation.
The pores in the concrete fiber are too small for water molecules to ingress and cause a problem.
The edges must be sealed to prevent moisture from passing as well because if it is not sealed it will nullify the effects of having the barrier there in the first place
Epoxy for Walls –
Epoxy acts as a protective and decorative paint to prevent moisture ingress on cement-based substrates, such as concrete, plaster, cement mortar, and cement boards.
The surface to be treated must be dry and stable, as well as be free from any materials that would hinder bonding, such as dust, loose particles, grease, etc.
Pool Liner –
Using a pool liner before the addition of soil and other substrates on a garden bed can help prevent water from going in the wrong direction.
The plastic pool liner should be placed on the wall surface closest to the house where the garden is to be located. The garden is then constructed on this liner moving outwards from the walls of the house.
Bitumen Paint –
Bitumen paint acts in a similar manner to epoxy, which coats and protects the wall’s surface against the negative effects the bare dirt can have on a wall.
It is very cheap, readily available, and can be easily applied using a paintbrush.
Tree Root Barrier –
A tree root barrier will not directly protect the wall from soil.
What it actually does is prevent roots from trees and plants from venturing close to your home by posing a hard barrier to prevent growth in unwanted directions.
Roots can cause cracks in the concrete structures and house foundations by absorbing moisture causing the soil to subside beneath the foundation. A void is created which removes the support from under the foundation causing stress and unwanted cracks.
Additionally, the roots themselves can place additional pressure on the foundation and walls as they grow bigger which also causes stress and cracks.
To find out more about roots and their effects on the concrete foundation you can see our detailed article here.
To Prevent Splashing of Soil onto the Walls –
Black Felt Soil Cover–
It will prevent moisture and will have a minimal cost to you.
Black felt is used to cover the topsoil which will prevent weeds and allow moisture to flow through the fabric into the soil.
It is a long-term solution to mulching that doesn’t require yearly replacement. It is applied on top of the soil and its amendments, after it is added to your garden bed.
The required holes are cut out where the plants are to be placed.
Use Mulch on the Soil –
Applying inorganic or non-soil mulches on top of soil can help prevent the soil from splashing onto the wall whenever the plants are watered or when rain falls.
Types of much to use
- Cedar bark mulch
- Stone Mulch
- Rubber Mulch
The Effects of Water on Concrete
Water can wreak havoc on this concrete material. Brick is extremely porous and as a result, it can absorb water like a sponge. Over time, water absorption can cause crumbling and cracking.
Additionally, moisture within the concrete structure can cause it to crack as it freezes during the winter months.
Water molecules expand when frozen and place tremendous stress on the pore structure of bricks and concrete causing it to easily crack under the strain over time.
Annual freezing and thawing weaken the concrete structure which will eventually lead to failure.
Rusting affects the concrete structure in the same way as water when it expands.
Concrete has high compressive strength but low tensile strength; therefore, reinforcing steel is often embedded in the concrete to provide additional tensile strength and ductility.
The iron from rebar material will rust as the iron reacts with water forming iron oxide.
The expansion of the iron rebar when it rusts also places a lot of stress on the concrete structure.
Understanding the Building Code and Weep Holes
Placing soil against a brick wall can produce some violations against the building code in the United States.
This violation comes when the weep holes from the brick are blocked by the soil you are going to use in the garden.
Codes require a minimum distance from the top of the soil to the bottom of the course brick to be at least 4″.
Weep holes allow air into the wall cavity, between the brick wall veneer and the inner wall framing, and also allow water out.
The weep holes are required in masonry walls at the top of the foundation wall, below all window and door sills, at the top of all windows, doors, and any other wall opening and are typically installed between 18 and 24 inches apart.
If the drain plane/ air space were not functional, water would not be able to drain downward and come out onto interior surfaces to create a water stain.
Therefore by having the weep holes clear you can protect interior walls and other surfaces from the effects of the build-up of moisture within the air cavity.
You can read more about weep holes with respect to building codes here.
The Effects of Concrete on Soil
Apart from water affecting the concrete structure, the concrete can also affect the soil by the chemicals it can release into the soil.
Plants can be affected by cement and concrete because the limestone (calcium carbonate) it contains can directly affect the pH of the soil by increasing its pH to high alkaline levels.
This increase in pH reduces the solubility of minerals within the soil making it less available for plants to absorb.
If you would like to know how concrete affects soil acidity and plant growth you can see our detailed article here.
Recommendations for Gardening Close to your home
- Air spacing around the house
Having a clear 4 feet distance around the home will allow for water to evaporate as air is allowed to flow.
- Don’t plant trees or vegetable gardens too close to home
Trees and vegetable gardens when planted close to the home can pose additional problems such as termites and root growth.
- Construct skirting around the home such that it slopes downwards away from the home
For water movement away from the foundation of the house a skirting should be constructed such that it slopes away from the house.
This causes water to run off away from the walls and foundation elimination the effects of water buildup close to the home.
- Answers from various forums suggest that the garden should not be constructed above the grade of the house to prevent water from getting into the house.
The dirt around the house should be removed in a grade and then new soil added for the garden to be planted.