Whenever a masonry structure is built, there comes a time when repointing needs to be done due to mortar deterioration. To replace eroded mortar, not all mortar types are used.
You’ll need to choose the right type for the job. The “right type” of mortar implies that there are several.
Here, we’ll be discussing extensively the types of mortar and which is best for a repointing job.
If you wish to carry out some repointing job immediately or seek to do so shortly, you should find this article very informative.
About Masonry Mortar
Mortar is binding material for masonry construction. It’s a workable paste consisting of fine sands, cement, and lime used for binding bricks, stone blocks, and other units of masonry.
Although the binding achieved by mortar lasts for an appreciable period of time, it eventually begins to disintegrate due to weather action.
So, why does old mortar disintegrate? One of the primary reasons for such is due to weather action. Weather action refers to a situation where water or moisture is absorbed into the brick structure.
Now, the continued freeze-thaw cycles that occur eventually weaken old mortar causing it to disintegrate.
Without repointing, the structure is sure to crumble. Repointing simply seeks to strengthen the structure to prevent further deterioration. Now, you want to make sure that the best mortar is used for repointing.
Doing otherwise would only amount to a waste of effort as the job done won’t last for long.
In determining which mortar type is best for repointing jobs, you’ll need to look at the different properties. These properties include the strength and extent of the bond.
These features determine how effective repointing jobs will be.
It’s important to also note that mortar needs to cure or bond both at the mechanical and chemical levels. How slow or fast does the best mortar cure?
A mortar’s compressive strength is also a factor that counts in determining whether it’s a good or a repointing job or not.
Mortar blends are also known as the types of mortar.
These include finishing mortar, stone laying mortar, lime mortar, cement mortar, gauged mortar, gypsum mortar, aerated cement mortar, Surkhi mortar, heavy mortar, mud mortar, and lightweight mortar.
Other types include type M mortar, type N mortar, type O mortar, and type S mortar. You also have packing mortar, fire-resistant mortar, x-ray shielding mortar, sound-absorbing mortar, and chemical-resistant mortar.
As expected, each mortar type mentioned has its particular uses.
However, we won’t be getting into such details but will narrow down to some of the most common types used for masonry projects such as repointing jobs.
Mortar Mix For Repointing
Repointing jobs are only performed when the structural integrity of the wall is intact. In other words, only a wall deemed to be structurally sound is considered for repointing.
Outside of that, the whole aim is defeated. So, which mortar type is considered the most suitable for a repointing job? You’ll need to read on to find out.
Type O Mortar to the Rescue
When it comes to the best mortar for repointing jobs, type O mortar easily beats the competition. It’s important to note that this only applies to repointing jobs. Type O mortar has a low compressive strength of 350 psi.
Although this type of mortar has a low structural capacity, its ease of application and consistency makes it the ideal mortar for repointing walls or existing structures.
There are several reasons why type O mortar is preferred for repointing jobs.
These include its elastic capacity, high hydrated lime content, and autogenous healing capacity. All of these features are crucial for perfect repointing jobs.
So, to further understand what they stand for, we’ll take a look at each of them.
Compressive strength is a common indicator for measuring mortar types. Mortars having high compressive strengths are known to be brittle.
The opposite applies to those with low compressive strength. These (mortars with low compressive strength) are less brittle, thus allowing for more elasticity.
During repointing, the bricks involved are older. This requires softer mortar with allowance for contraction and expansion. There’s no better mortar than type O when it comes to elasticity.
With temperature changes or stress, bricks can contract and expand without cracking mortar joints.
High Hydrated Lime Content
When you need a mortar that’s softer, yet having waterproofing capabilities, then type O mortar perfectly fits the bill. This characteristic is due to the high hydrated lime content within such mortars.
Also, less portland cement is contained within such mortar making them ideal for repointing jobs.
With high lime content, type O mortars serve to provide a better bond with older bricks. What more? The aim of repointing isn’t to support the compressive weight of brickwork.
Rather, it’s to ensure that the brickwork is held in place or bonded. Here, mortars with high hydrated lime content such as type O are perfect for repointing.
Autogenous Healing Capacity
Another attribute of high lime mortars is the autogenous healing capacity they give to type O mortar. Simply put, type O mortars have the capacity to heal.
This is an impressive feature that ensures that cracks do not develop.
So how does autogenous healing unfold? There has to be a crack for this to happen. Here, atmospheric carbon dioxide reacts with rainwater resulting in dissolved hydrated lime.
This is re-carbonated, thus sealing or healing the crack.
This interesting chemical action happens each time a crack appears, thus making type O mortars the best for repointing jobs.
A Repointing Job Needs to be done properly Too
It’s never enough to have the best mortar without performing a thorough repointing job. Here, we’re referring to having the necessary masonry skills. If you don’t, you should leave such to the experts.
Only consider reputable masonry contractors for your repointing job. Remember, repointing saves your structure from further deterioration. As such, it must be properly executed.
The best mortar for repointing has been mentioned and discussed. We’ve seen that there are different types of mortar each serving a specific purpose. Now, you’re not in doubt about what mortar type to use.
All you have to do is proceed to fix your receding mortar joints.