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What is Parging?
Parging is a Portland cement, lime and sand based sacrificial layer or “skin” coating the exposed foundation (and typically 2-4 inches below grade) of a home or building with a poured concrete or block foundation. The main purpose of parging is to serve as a decorative appearance, providing your foundation a smooth finished look with a nice sanded texture that is appealing to the eye. Parging also acts as a water resistant barrier keeping your foundation protected from the elements and deterioration as well as resisting moisture from entering your home.
On concrete block foundations, parging is applied below grade to provide a smooth finish for a proper waterproofing coating or membrane.
Life of Parging
It is important to understand that parging is sacrificial and will eventually fail over time. A properly parged wall done by a skilled mason in the right weather conditions can last a very long time. However, with our harsh Ottawa winters and extreme temperature fluctuations, a well parged foundation unfortunately will fail eventually where it is exposed to water, snow and the worst enemy of all- salt.
A parged wall that is not exposed to harsh weather or foundation movements in our cold climate can expect to last 20+ years before it begins to show signs of damage. However, a set of front steps or the piers of your front garage, where there is a lot of water and snow exposure or gets salted routinely in the winter may only last 3-5 years before it begins to crack or fail.
Our Procedure
At Kavanagh Masonry, our procedure is based on years of experience in the field and through the Red Seal Program to determine an installation process that works best for our weather conditions keeping your foundation protected and looking aesthetically pleasing.
Cleaning
First the wall must be prepped by cleaning off any impurities that will affect the parging bond. This is typically done by scrubbing the wall with a steel brush and removing debris with a small air blower. In extreme cases, a pressure washer may be needed to clean the foundation of dirt and debris caught in the wall’s pores. At this stage, any old loose parging is to be removed with pneumatic chippers or by hand with a cold chisel. If the wall surface is not made from a masonry product, diamond wire mesh is installed for the parge to adhere to.
2. Dampen Bonding Surface
The next step is to wet the wall down carefully. The wall needs to be thoroughly wet but not too wet that the pores in the wall are completely filled with water. Then the parging will have nothing to bond to. Keeping the wall wet will allow the parging once applied to bond properly and cure slowly. The slower the parging can cure, the stronger it will be.
3. Mix Parging
A parging mix is then prepared. A skilled mason will be able to determine the right consistency and ingredients (Portland Cement, hydrated mason’s lime and sand) used to ensure a mix that can be applied easily and give a consistent look to the wall. Once the mix is prepared, the mortar is trowelled on to the wall with good pressure to ensure the mortar is bonding into all the pores and craters that may be on your wall.
3. Scratch Coat
The parging is done typically in a two coat application. Sometimes one coat is sufficient, however in most cases, the first coat acts as the leveling surface. All the pockets or craters in the foundation will be covered and leveled to a flat plane. These areas where the mortar was applied thick will cure slower than thinner parts on the wall. This uneven curing can cause the wall to look blotchy and oftentimes is the culprit for hairline cracks to form. This first coat is known as the scratch coat and is applied anywhere from 1\8’’ to 3\8” in thickness.
4. Final Coat
After the scratch coat has cured sufficiently, it is time to apply the second and typically final coat of parging. This coating is applied in a thin layer and is meticulously applied as evenly as possible to ensure the finished look will be flat and corners will be square and vertically true.
5. Float Finish
Once the final coating has dried to a proper hardness determined by the mason, the surface of the parging will be floated with a wet sponge float evening out the parging and providing a smooth, often circular texture to the wall that is consistent and pleasing to the eye.
6. Damp Cure
The last final stage is to damp cure the wall. As stated earlier, the slower the mortar cures, the stronger it will be. If parging mortar sets too fast, it can result in cracking and the parging will fail. After the final float, the wall is misted several times with water. The wall is kept damp and shaded from the sun using moistened burlap and sheets of plastic that will cover the wall for at least 3 days while the parging cures. Slowing the evaporation of moisture will make the final wall strong and beautiful. Parging takes 60-90 days to fully chemically cure and the wall may appear blotchy until it has fully finished curing.
For parging to last and look good, it needs more than a quick DIY repair. Do you need your foundation parging repaired? To have your parging done the right way by a Red Seal Certified Mason, get the quoting process started today on our Request a Quote Page.