Complete Guide to Mortar Mix Ratios For Common Projects

Written by Daniel Woodley. Fact checked by Paul Farley. Published to Hard Landscaping & Building on the 5th November 2023.

Our editors publish helpful guides and insights learnt from years of experience. They also test, review and suggest garden products. If you buy something via links, we may earn a commission, but we never accept products or incentives from manufacturers. Learn about our process.

I’ve worked in several building trades over the years, including roofing, building and landscaping.

In this guide, I’ll disclose the mortar mix ratios I use for various projects.

There aren’t any blanket industry-wide standards as every project is different; the type, composition and strength of the structure, brick or surface you are mortaring onto must be taken into account as must the expected weathering from wind-driven rain.

Understanding The Lingo

I’ve found that different tradespeople use different language to describe stuff so here’s a quick explanation so we are all on the same page:

Cement: A grey powder which is combined with sand and possibly other materials to form concrete or mortar. Portland cement is popular while other brands may include additives such as a plasticizer. On this page, I will only suggest portland cement.

Mortar: Consists of a blend of cement, very fine sand, water, and sometimes hydrated lime (in period buildings, hydraulic lime is used instead of cement). It is primarily used in masonry and the filling of joints. This compound is applied in thin layers since thicker applications are prone to cracking as they dry.

Concrete: Similar to mortar but includes larger aggregates (stones) to prevent cracking when the mix dries and to provide rigidity.

Building Sand: Also known as soft sand, it possesses a finer texture and is employed for tasks like masonry, filling gaps, and cases where slim mortar layers are necessary.

Sharp Sand: This has a grittier texture than building or soft sand and is ideal for use with other sands to enhance the mix and avert cracking while drying. It is typically utilized in scenarios requiring a marginally thicker mortar layer—for instance; I always use this mix when securing chimney pots, setting roof tiles, and various landscaping tasks where the layer required is thicker.

Plasterer’s Sand: Neither as gritty as sharp sand nor as fine as soft sand, but undergoes a washing process to eliminate any salts and clay remnants that could lead to efflorescence, which is the crystalline deposit of salts that can form when water is present.

Hydraulic Lime: Not to be mistaken with the fruit, it is a building material with a history stretching back to Roman times and is still employed today as a stand-alone binder in mortar mixes used on traditional buildings made of softer, more porous bricks. It’s also breathable, unlike cement-based mixes.

Hydrated Lime: An additive that makes mortar easier to work with. It’s often used instead of plasticizer.

Plasticiser: This is a fluid incorporated into mortar to enhance its workability and extend its setting time slightly, producing a stickier mixture that’s easier to spread and shape with a trowel. If you’re new to working with mortar, I suggest adding this to the mix as it will it easier to work with.

Waterproofers: Helps to waterproof the mix.

Depending on the specific requirements, additions like frostproofers, accelerators, and colourants may also be integrated into the mixture.

Update: Rapid Set Cement is a cement which sets very quickly (15 minutes). While it does have its uses, I’ve found that it can cause issues, especially for novices who aren’t used to working with cement that goes hard so fast. I’ve met quite a few labourers who have stuck their trowel in a bucket of cement!

What Happens if the Wrong Mortar Mix is Used?

I took this photo many years ago, you can clearly see the mortar has crumbled to dust:

Crumbly mortar

All of the roof ridge tiles on that property were at risk of blowing off in the wind. The reason? Incorrect mortar mix ratios – it should have been 3 x sand to 1 x cement but it was closer to 10:1 ratio, by my estimate.

I also took the photo below, which shows what can happen when a thick layer of mortar is laid and that mortar doesn’t contain sharp sand:

Cracked mortar

(Sharp sand stops the mix from cracking like this)

Bricklaying Mortar Mixes

I have always followed the classic advice which is never to create mortar that is stronger than the bricks.

If something is to fail, it should be the mortar, as this can be repointed/repaired in the future.

Damaged bricks are far more difficult to replace.

With that rule in mind, I generally use these ratios:

Hard bricks: 4 building sand to 1 cement with plasticizer.

Soft bricks: 5 building sand to 1 cement with plasticizer.

Very soft bricks: 6 building sand to 1 cement with plasticizer.

Period bricks: Replace the cement with hydraulic lime. The exact ratio will depend on the type of bricks and the texture of the sand.

When working with mortar, I always considered the hardness of the bricks and how much driving rain the wall would be subjected to.

For example, when repairing a chimney in an exposed location, I would increase the amount of cement as a weak mix is more likely to wash out after years of heavy rain.

I would also consider what the purpose of the wall is. For example, a load-bearing wall under a DPC (where it will get wet) could be as strong as 3:1.

There’s no set blanket rule as the type of bricks, purpose of the wall and exposure to the elements must be taken into account.

Best Mortar Mix For Repointing Walls

I have always used between 4 parts building sand and 1 cement and 6 parts building sand to 1 cement for general wall repointing. The exact ratio will depend on the softness/hardness of the bricks and any wind-driven rain. 4:1 would be my standard mix for repointing (plus plasticizer as required).

On chimneys and walls in very exposed areas, I would go down to 3½ parts building sand to 1 cement, assuming the bricks were hard.

On period brick, I would use hydraulic lime and building sand at a ratio between 3:1 and 5:1 depending on the strength of the lime, the brick and the circumstances.

Ratio For Patio Slabs and Patio Repointing

For bedding patios, any mix between 4:1 and 6:1 will suffice.

To prevent cracking, I have always added sharp sand to the building sand.

A typical mix I have often used is 3 parts sharp sand, 2 parts building sand and 1 part cement.

For repointing, I would always go slightly stronger at 4 parts building sand and 1 part cement. I would only include sharp sand if the joint was very thick.

(I would generally add plasticizer as required)

Roofing Mortar Mixes

Two things must be considered when using a mortar mix on a roof:

  • The area is subject to more rain than most other locations.
  • The mix is often laid much thicker, so it must contain sharp sand to stop cracking.

Thick layer of chimney flaunching: I’ve often used 2 parts sharp sand, 1 part building sand and 1 part cement.

Ridge, valley and verge tiles: 2 parts building sand, 1 part sharp sand and 1 cement.

I would consider a weaker mix if working with period tiles that are very soft.

(I would also add plasticizer as required)

Mortar-bedding a roof ridge

Bedding ridge tiles onto a 3:1 mortar mix

Wall Rendering

There is a golden rule I have always used when mixing render:

The mix must never be stronger than the material you are rendering onto.

I have used two mixes in the past.

The “classic” mix:

3 parts rendering sand and 1 part building sand with 1 part cement for the first coat (called a 4:1 scratch coat).

The second coat (called a float) is usually 5 parts rendering sand to 1 part cement with plasticizer (this is a 5:1 float coat).

In recent years, I’ve met tradespeople who are using a 6:1:1 mix:

5 parts rendering sand, 1 part building sand, 1 part hydrated lime, 1 part cement for the first scratch coat.

6 parts rendering sand, 1 part hydrated lime and 1 part cement for the second float coat.

I’ve never seen an issue with the render cracking when these mixes were used but all the buildings I’ve worked on were modern.

Cement-based renders should not be used to replace lime-based renders on period buildings as this may trap moisture in the wall. If you are working on a period building, consult with a specialist who can inspect the original materials and suggest a ratio that will include hydraulic lime.

Floor Screeding Mix

A 3:1 sharp sand/cement ratio would create a high-strength floor but I’ve only ever worked with teams that have used 4 parts sharp sand to 1 part cement and this is perfect for domestic projects.

5:1 is also acceptable for light foot traffic areas (i.e domestic).

(Adding plasticizer to the above mixes is fine)

For period buildings, cement should not be used as a like-for-like replacement for lime-based floors as it may push moisture toward the edges of the floor where it may rise into the wall. A good starting point for period floor screeding is 2½ aggregate to 1 part hydraulic lime but one should consult a period building specialist first.

Author: Daniel Woodley

Daniel has over 18 years of experience in the construction, home improvement, and landscape garden industries.

He previously worked as a project manager and has experience in managing teams of tradespeople and landscape gardeners on both small and medium sized projects.

Daniel is also a keen gardener and enjoys growing unusual plants and tending to his lawn.

More About Daniel Woodley.

Daniel Woodley

Why Trust Us? Our Experience

At DIY Gardening, we follow a detailed, rigorous process to create content that is helpful, factually correct and meets the highest standard of integrity.

Our 5-step process is:

1) We select a topic that we feel will help our readers.

2) The author creates the content based on their knowledge and experience of the subject or product.

3) We ask an expert with qualifications in the relevant area to fact-check and review the content, which we update accordingly, if applicable.

4) The content is checked by the site owners and published.

5) We review the content yearly to ensure it’s still correct and relevant.

Daniel Woodley wrote this guide to mortar mix ratios. Daniel is a qualified landscape gardener and has many years of experience in this field and also in construction, where he worked initially as a roofing contractor and then as a project manager.

As accuracy is important, we asked Paul Farley to review and fact-check this guide.

Explore: Paul Farley’s profile and qualifications.

Find out more about the team behind DIY Gardening

About Us

Hannah Miller
Danny Woodley