Mortar Mix Ratio Converter

Mortar is a mixture of cement, lime, and sand used to bond bricks, blocks, and stone in masonry construction. Different mortar types have different strength and flexibility characteristics suited to different applications.

Standard mortar types and their mix ratios (by volume):

The sand columns are ranges rather than single numbers on purpose, and the next section explains where they come from. Charts that print one figure per type have picked a point inside these bands and thrown the band away.

When to use each type:

• Type M (Mason): Highest strength. Used for below-grade applications, foundations, retaining walls, and driveways. Best where the mortar contacts the ground.
• Type S (Strong): High strength with good bonding. Used for exterior walls at or below grade, patios, chimneys, and areas subject to wind pressure. The most versatile exterior mortar.
• Type N (Normal): Medium strength, most commonly used mortar. Ideal for above-grade exterior walls, interior walls, and general-purpose masonry. Offers the best balance of strength, workability, and durability.
• Type O (Office): Lowest strength, very flexible. Used for interior, non-load-bearing walls and for re-pointing historic buildings where soft mortar is needed to protect old bricks.

The rule of thumb for remembering types: The letters M, S, N, O come from the words “MaSoN wOrk” when you take every other letter.

The sand quantity is not a fixed number, it is a ratio to everything else. ASTM C270 sets the sand at 2.25 to 3 times the combined volume of cement and lime, which is why the sand column climbs as the lime does. Type N carries one part lime to one part cement, so two parts binder, so 4.5 to 6 parts sand. Type M carries a quarter part of lime, so 1.25 parts binder, so 2.8 to 3.75 parts sand. Get that relationship and you never need to memorise the table: work out the binder, multiply by about 2.75, and you have the sand.

Going below 2.25 makes a mix that is over-rich, expensive, and more likely to crack as it shrinks. Going above 3 leaves too little paste to coat the grains and the mortar goes harsh and crumbly on the trowel. The middle of the range is where masons actually work.

How lime affects mortar:

• More lime = softer, more flexible, easier to work with.
• Less lime = harder, stronger, but less forgiving.
• Lime improves water retention, which helps the mortar cure properly.
• Historic buildings used lime-only mortar (no Portland cement), which is much softer.

Mixing tips:

• Always measure by volume, not weight. One shovel of cement to the appropriate number of shovels of lime and sand.
• Mix dry ingredients first, then add water gradually until the mortar reaches a peanut-butter-like consistency.
• Mixed mortar stays workable for about 90 minutes. Do not add water to re-temper mortar after this time.
• Sand should be clean, well-graded masonry sand, not play sand or beach sand.

Why the batch never yields as much as you added. Add a cubic foot of cement, a cubic foot of lime and five and a half of sand and you do not get seven and a half cubic feet of mortar. The cement and lime paste disappears into the spaces between the sand grains, which are about a third of the sand’s bulk volume, so the finished yield comes out close to the sand volume alone. That is the working rule on site: order sand by the volume of mortar you need, and treat the cement and lime as things that fill the gaps rather than things that add bulk.

A note on bag sizes, because they differ by country and by product. A US bag of Portland cement is 94 lb and holds almost exactly one cubic foot, which is the whole reason the proportions are quoted the way they are: one bag is one part. A UK or European bag is 25 kg, roughly 0.6 cubic feet, so a “one bag” recipe does not carry across. Hydrated lime comes in 50 lb bags at about 40 lb per cubic foot, so a bag is roughly 1.25 cubic feet.

Masonry cement and mortar cement are a different route to the same place. Both are Portland already blended with lime and air-entraining agents, sold as Type N, S or M in the bag, and used one part cement to three parts sand with no separate lime. They are quicker and more consistent, and they are what most bricklayers actually buy. Mixing your own from Portland and lime gives more control and is usually cheaper by volume. The strengths in the table apply either way, because the type letter refers to the finished mortar rather than to how you got there.

Water is the one ingredient nobody should measure. Every other component is proportioned, but water is added by feel to a consistency, because sand carries a variable amount of moisture already and a damp pile needs less than a dry one. Aim for mortar that holds a ridge on the trowel without slumping. Roughly six to seven gallons per bag of cement is typical, but treat that as a sanity check on what you have poured in, never as a recipe.