Mortar Mixing – What is The Best Mix Ratio?

This page is part of our blog and is all about mortar mixes for home improvement and construction projects.

Whether you’re laying bricks, pointing, renewing chimney flaunching, laying screed or rendering, we have the best mix ratios for you.

Tradespeople and builders often use different terms to describe cement, concrete and mortar, so here’s a quick guide designed to avoid confusion:

Cement is a greyish coloured powder that is mixed with sand and/or other aggregates to create concrete or mortar.

Mortar is a mixture of fine sand particles, cement, water and sometimes lime. It’s typically used for brick laying and pointing. It is usually laid in thin layers as thicker layers may crack during the drying process.

Concrete is a mixture of aggregates such as crushed rock, gravel and sand that is mixed with cement and water. Concrete is usually laid in thick layers, the larger particles prevent cracking during the drying process.

Soft sand is also known as building sand and contains fine grains of sand and is used for bricklaying, pointing and where thin layers of mortar are required.

Sharp sand is more coarse than building/soft sand and is perfect for mixing with other sands to prevent cracking during the drying process. It’s often used in situations where a slightly thicker layer of mortar is required – chimney flaunching, bedding roof tiles and many garden projects will require sharp sand.

Plasterers sand is not as coarse as sharp sand but not as fine as soft sand. It’s washed to remove salts and clay residue that could cause efflorescence (salting).

Lime can be used as an alternative to cement in some mixes or used in conjunction with it. Lime allows materials such as bricks to breathe, it’s commonly used on older period buildings with soft, permeable bricks that would likely crack if cement was used.

Plasticiser is a liquid that is added to the mix to make the material easier to work with and it also slows down the curing process slightly. It makes a typical mortar mix sticky and easier to point over.

Waterproofer is different to plasticiser. Does what it says on the tin and is often used when rendering.

Frost proofers, accelerators and colour additives can be included in the mix as required.

What Happens if You Get the Mix Wrong?

The photo below shows a ridge tile that was bedded onto a very weak and totally unsuitable mortar mix.

The tile was not secured in place and the “mortar” could be crushed into small particles by simply squeezing it in my hand:

The photo below shows cracked mortar – typical issues that can occur if the mix is too strong:

Best Mortar Mixes

Below you’ll find our guide to mortar mixes:

Bricklaying

The best mix will depend on the type of brick and the location of the wall. For most domestic builds such as house building, use one of these mixes:

4 parts soft sand with 1 part cement, add water and plasticiser.

For soft older bricks, 5 parts sand, one part cement and one part lime.

For retaining walls or anywhere likely to be in regular contact with water, 3 parts soft sand and one part cement, 1 part lime is optional depending on the type of brick/block.

For Airtec blocks above DPC, 6 parts soft sand, 1 part cement and 1 part plasticiser or 5 parts soft sand and 1 part cement.

For blocks below DPC, 4.5 parts soft sand, 1 part cement and 1 part lime or 4 parts soft sand and 1 part cement

This page contains a price guide for wall repointing.

Chimneys

For chimney repointing the best mix will depend on how exposed the chimney is and it’s location. For chimneys in wind swept rainy parts of the country use a mix of 3 parts soft sand and 1 part cement. For softer, older or more permeable bricks, 4 parts sand, 1 part cement and 1 part lime can be used. Plasticiser is optional.

Chimney flaunching will receive a lot of rainfall so the mix should be strong, this prevents it washing out. Because flaunching is laid several inches thick, add sharp sand to the mix to avoid cracking during the drying process. 2 or 3 parts soft sand 1 part sharp sand, 1 cement and half-part lime is optional.

or

1 part soft sand, 2 parts sharp sand, 1 cement, half part lime is optional.

Chimney maintenance costs are published on this page.

Paving Mortar Mix

For bedding under the slabs use 5 parts sharp sand, 1 part soft sand and 1 cement.

For pointing use 4 parts soft sand and 1 part cement. For high traffic areas, a stronger mix of 3 parts soft sand and 1 part cement can be used.

This page contains a price guide for a new patio.

Render Mortar Mix

The first coat of render should ideally be slightly stronger than the second coat. While some tradespeople make the two mixes the same strength, the second coat should never be stronger than the first coat.

A pure soft sand mix shouldn’t be used when rendering. It’s preferable to use either sharp sand, plasterers sand or a mixture of two. Soft sand can be added to the mix but we feel it shouldn’t comprise more than 25% of the entire mix.

The first coat of render can be 2 parts plasterers sand and 2 parts sharp sand, 1 part cement and half part lime. Waterproofer can be applied to the first coat.

The second coat must be slightly weaker than the first, so 3 parts plasterers sand, 2 parts sharp sand, 1 part cement and half lime. Plasticiser can be used in the second coat.

For locations in the east and south of the country or any sheltered location that experiences less windswept rain, a slightly weaker mix can be used. For the first coat 4 parts sharp/plasterers and for the second coat 5 parts sharp/plasterers.

This page contains a guide to rendering prices in the UK.

Floor Screed Mix

4 parts sharp sand and 1 part cement. Although anything from 3-5 parts sharp sand to 1 part sand would be acceptable for most situations.

Best Mortar Mix For Roof Tiles

Because roof tiles are located in an exposed location that’s likely to experience rainfall, a strong mix should be used. Unfortunately, some profiled roof tiles require a very thick bedding of mortar, so to reduce the risk of cracking, sharp sand should be introduced to the mix for most tiles.

All tiles except Plain tiles – 2 parts soft sand, 1 part sharp sand and 1 part cement.

For tiles where only a thin bedding of mortar is required (i.e. Plain tiles) 3 parts soft sand*, 1 part cement and plasticiser.

*we recommend choosing a soft sand that is fairly coarse, avoid soft sands that are at the “silty” end of the spectrum.

Don’t forget; to meet new British Standards requirements for roof fixings, you cannot rely on mortar to secure the tiles in place. Ridges, valley tiles and verges should be secured with a nail or clip, either in addition to the mortar in replacement of it, this is called a dry fix method. This page contains information about the differences between a dry and wet fixing method.

Roof repair prices can be located on our main price list here.

Water Content – How Much is Too Much?

The firmness of the wet mortar can be altered by changing the type of sand, the sand/cement ratio and the amount of water added to the mix.

Most bricks and blocks are quite porous and as only a thin layer of mortar is required, a wet or “sloppy” mix is often preferable.

Some roof tiles require a bedding layer of mortar that’s several inches thick and a wet/sloppy mix wouldn’t be suitable, it would slump off the tile. For roofing projects, a firmer mixture is required.

Needless to say that mortar should never be so firm that it doesn’t have enough water content to create a chemical reaction. Neither should it be so sloppy that it’s impossible to work with.

Additives

Frost proofer should not be relied upon to protect mortar from freezing conditions. It can be used but its reliability is debatable.

Colourants can be used but only use as much as you need and avoid excessive amounts.

Accelerators speed up the drying time but often leave you with little time to work with the mortar before it starts to set. If you continue to work with a mortar that has set, you’ll reduce the strength of the finished mortar. Therefore, you should only use them when absolutely necessary and not as a matter of course.

Concrete and Ready Mix Prices

If you don’t want to mix the materials yourself, you can get it delivered by a ready mix supplier.

This is the perfect option for large projects.

See ready mix concrete prices here.

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