Rosie on the House TOP FAQ- What is the correct Mortar Mix ratio for Masonry?

Clem Hellmann of Quality Block and I agree that with pre-mix bags available, unless you are on a major jobsite with at least a dozen masons it's just not worth mixing yourself. However, if you are inclined to do so our friends at Superlite Block have provided the industry standard directions below.

There are a variety of mortar mixes that the mason contractor can mix up, depending on the type of material that is being installed:

* Type M (2500 psi)
* Type S (1800 psi)
* Type N (750 psi)

The different types are achieved by varying the ratio of Portland Cement, Lime and Sand. Type S mortar is the most common for the Arizona market so we will use this as the basis for our comparisons.

There are three primary ways to make mortar:

1. Portland Cement, Hydrated Lime and Masonry Sand
2. Masonry Cement and Masonry Sand
3. Pre-mixed Mortar

The Portland Cement, Hydrated Lime, Masonry Cement and Pre-mixed Mortar are available in bags, the Masonry Sand is generally available in “bulk quantities” that are delivered by a truck or can sometimes be purchased in big “super sacks” from the big box retailers.

Portland Cement
94# bags
Lime
50# bags
Masonry Cement
70# or 78# bags
Pre-mixed Mortar
60#, 80# or 94# bags
Masonry Sand Usually a pile of sand is delivered to the jobsite by a dump truck. The sand is measured into the mixer by means of a standard square point shovel that is “mounded full”. This is referred to as a “shovel of sand”

Portland Cement, Lime and Sand

This is the “old school” method, the standard for the industry that all other methods are compared to. In order to make a Type S masonry mortar one would proportion the materials into the mixer in this manner;

1 bag
94# of Portland Cement
½ bag 50# Hydrated Type S Lime
28 “Shovels” Masonry Sand
7 to 8 Gallons Clean Water

Mixing Procedure:

* Put 2/3 to 3/4 of the water into the mixer
* Add the Portland Cement and Hydrated Lime to the batch
* Add the sand into the mixer, adding water as necessary to achieve the desired consistency
* Mix for 5 minutes in a mechanical paddle type mixer

Amount of water required to make good mortar will vary depending on the desired consistency of the mortar. For stiff mortar use less water, for wet mortar use more water. If you do not add enough water the mortar is so stiff that it is unworkable and very difficult to use, if you add too much water the mortar turns to “soup” and you will be unable to use it.

Masonry Cement

Masonry Cement is simply a product that has Portland Cement and Hydrated Lime already blended together in the proper proportions. In order to make a Type S mortar with Masonry Cement one would proportion the materials into the mixer in this manner:

1 bag 70# or 78# Masonry Cement
18 to 20 “Shovels” Masonry Sand
5 Gallons Clean Water

Mixing Procedure:

* Put 2/3 to 3/4 of the water into the mixer
* Add the Masonry Cement to the batch
* Add the sand into the mixer, adding water as necessary to achieve the desired consistency
* Mix for 5 minutes in a mechanical paddle type mixer

Add water to achieve desired consistency of mortar, less water for stiff mortar, more water for wet mortar.

Pre-mixed Mortar

This is the easiest mortar of all to make. Pre-mixed mortar is a combination of Portland Cement, Hydrated Lime, and Masonry Sand already blended together in the proper proportions to make a Type S mortar. All that is needed is to add sufficient water to achieve the desired consistency, usually about 5 to 6 quarts for an 80# bag. Pre-mixed mortars are a little unique in that they require a slightly modified mixing procedure.

Mixing Procedure

* Put 2/3 to 3/4 of the water into the mixer
* Add the Pre-mixed mortar into the mixer, adding water as necessary to achieve the desired consistency
* Mix for 3 to5 minutes, turn off the mixer and allow mortar to “slake” for 2 to 3 minutes, re-start the mixer and mix for an additional 2 to 3 minutes adding water as necessary to achieve desired consistency.

Pre-mixed mortars use a kiln dried sand that has a higher water demand. It takes a few minutes for all of the water to be absorbed into the dry sand, hence the need for a prolonged mixing time. If you do not allow the mortar to set and “slake”, it will feel gritty on the trowel and will be difficult to work with.

All of these mortar may be mixed by hand in a wheelbarrow or “mud tub” for those of us who do not own a mixer. A mortar hoe is a great tool when mixing by hand, as well as the obligatory square point shovel. I have found from past experience that a standard construction grade wheelbarrow is too small to mix a full bag of Portland Cement, ½ bag of Hydrated Lime and 28 shovels of sand. It will just barely fit 1 bag of Masonry Cement and 18 to 20 shovels of sand. A standard wheelbarrow very comfortable fits 3 of the 60# bags of Pre-mixed Mortar, or 2 of the 80# or 94# bags of Pre-mix Mortar. Follow the same mixing procedures as when using a mechanical paddle mixer.