Getting the Best Possible Mortar Match for Masonry Repair

Exposure to harsh deicing salts, unforgiving Winters and volatile Spring weather can cause Ottawa masonry, whether its brick, block or stone, to deteriorate. Many masonry systems require a basic maintenance repointing, or a few minor brick replacements up to complete rebuilds to bring integrity back to your brick or stone structures.

When performing brick or stone restoration and repair work, it's important that the mortar blends in with the existing masonry as close as possible. The expectation when matching mortar is that it may never be a perfect match. Unless the sand is quarried from the exact site as the original and the cement and lime fired in the exact same kiln, you are already starting out at a disadvantage. Below is described the best process for getting a close mortar match on most structures. If carrying out a huge heritage project, it is advised that mortar samples be sent off to a lab for analysis to get the proper composition required to replicate.

Getting the Recipe Right

Modern mortars vary based on their usage and history. The most common mortar recipes used are named by type. There is type M, S, N, O and K. Each of these types vary based on ratios of sand to lime and portland cement. Type M and S are richer in cement versus lime and so they have a higher compressive strength and durability. They are typically used below grade. Type N is a standard brick mortar with equal portions of lime to cement making it the middle ground for compressive strength, elasticity and durability. Type O and K are lime rich mortars that boast a higher elasticity and breathability.

When choosing a good mortar match, it is important to use the right prescribed ratios to get a good match as the cement to lime ratios can affect the final shade of colour with cement dominant mortars often curing to darker shades versus lime rich mortars.

Most modern brick homes are built using type N mortars while block work is done in a type S. Most historical and heritage work uses lime mortars similar to a type O or type K. Determining the right mortar for small projects is often at the discretion of the mason which is why it is always recommended to choose a reputable masonry contractor to repair brick and stone on your home. Choosing the wrong recipe for a mortar repair can cause moisture problems and irreversible damage to softer masonry units.

Dyes

Many mortars are dyed to add aesthetic appeal to blend or contrast the masonry. You don't have to look far to see coloured mortars used all over Ottawa like the black/charcoal mortars used to repoint Parliament Hill or the brick red dyes used on the beautiful historical homes of the Glebe.

Getting in touch with a local Masonry Supplier will provide you usually with colour swatches of all the common dyes used in the area. Bringing in a sample of your old mortar is the best way for them to help you find a good dye match for the job.

Mixing

Once you determine the right recipe and narrowed down your dye options. Prepare the mortar without the dye. Take a piece of the original mortar and wet it by dunking it in water. Take a trowel worth of dye and sprinkle a little bit of the dye into the mortar. You can always add more dye but you can't take it away so it's important to go slow and mix the mortar carefully. Keep your original sample from drying out and continue to add dye to the mortar until you achieve the depth of colour of the wet original sample. The theory is that when the new mortar dries/cure it will brighten to the shade of your dry original mortar sample. Multiple dyes may need to be mixed and matched with different trowels of mortar until you find the right portions to achieve the best match before mixing the dye into a full batch of mortar. 

Brick & Stone corner repair: Note the darkness of the fresh mortar versus the original. In 60 days it will brighten up and blend in.

Curing & Patience

Mortar typically takes roughly 28 days to reach its final compressive strength but can take over 60 days to fully carbonize. Lime rich mortars often take up to 90 days or longer to fully carbonize. During this curing time, the new mortar will continue to brighten up to match the existing mortar.

Some mortars may remain visibly distinct from the existing due to weathering and sunlight creating a patina on the existing original mortar that is unachievable using colouring. Sometimes all a mortar needs to blend in is time for the sun to recreate a natural patina.

Hire a Professional Local Mason

Mortar matching can be a tedious and messy process for the inexperienced which is why it is always recommended to hire a licenced reputable masonry contractor for brick repair, stone repointing and chimney repairs. Choosing a local small company with years of service in your area means you will be hiring a mason that has experience using the common dyes in your neighbourhood. If you are in the Ottawa area and looking to get your masonry restored, please reach out to us on the Request a Quote page or contact directly at 613-859-5090.