Mortar Mixes
Standard Mixes
Mix ratios are by volume, not weight.
3:1 sand:cement
Strongest cement & sand mix. Mixes with more cement microcrack on setting, giving lower strength.
4:1 - 7:1
Weaker mixes from 4:1 to 6:1 and sometimes 7:1 are used for walls, drives, bedding brick edging, etc
1:3:5 cement:sand:aggregate
Strong concrete mix
1:2:9 lime:cement:sand
A lime and cement mix that can sometimes fail prematurely. Not recommended.
1:1:6 lime:cement:sand
A lime & cement mix good for brickwork
3:1 sand:lime
Lime mortar for historic brickwork & stone walls. Avoids damage to soft brick & stone. Mixes used are often anything from 2:1 to 3:1.
Dry Mix
Mortar mixes are often used dry for bedding fence posts. Rain and water within the soil will gradually set the mix, and the aggregate content keeps the post stable whether its set or not. A dry mix is immediately mechanically stable, whereas a wet mix is more likely to allow the post to move until set.
More Mixes
There are many additives and alternatives that have been used in mortars.
Clay
Clay, sand & cement makes a cheaper lower energy mortar. Clay content makes for less ideal handling characteristics.
Silt
River silt has been used in place of sand. The result is a strong mortar with less consistent strength than graded sand based mortar.
Black Mortar
Coal ash with or without sand, plus lime makes black mortar. Long known for tendency to premature failure. Used to be popular in Northern industrial areas, where large quantities of coal ash needed disposal.
Fibre reinforced cement
Fibres added to sand & cement increase tensile strength and control cracking.
Many fibres can be used, the most popular is now alkali resistant glass fibre. Asbestos fibre used to be the most popular until the mid 80s.
Polystyrene
Sand, cement & finely shredded expanded polystyrene make a lightweight insulating mix.
Aerated cement
Sand, cement & aluminium powder make a lightweight insulating mix.
No fines concrete
Cement, water & stones makes a highly porous 'no fines' concrete.
- Used to be used for interior construction blocks.
- Occasionally used to facilitate floor drainage.
- Vulnerable to freeze-thaw cycle damage
HAC
High Alumina Cement
Stabilised Earth
Subsoil & cement.
Subsoil & lime has also been used, but is not as strong.
Topsoil & cement mix is used for gravel drives. The cement is simply sprinkled and raked in before the gravel is laid. This discourages weed growth and gravel sinking into the mud.
Sand, cement & pozzolan
Any of various Pozzolans may be used. Pozzolans reduce the amount of cement needed in the mix. Some pozzolans, such as PFA, make the concrete corrosive to copper pipe. Upto 30% of the cement can be replaced with a pozzolan. Use of pozzolans reduces pH of the set concrete, and modifies its performance properties in some respects.
Semi-dry mixes
Final strength depends on water content, with drier mixes yielding higher set strengths. Semi-dry mixes are widely used industrially, They require force to compact. Paving slabs for example are often made from hydraulically pressed semi-dry mixes.
Waste core
Stable non-hazardous waste can be incorporated into bulk concrete to reduce costs and dispose of the rubbish.
Rock fill
Where cost is critical and rocks plentiful, mixed rocks can be incorporated into the final product. This can reduce concrete use by 2/3 or more. Suited to large concrete constructions such as house foundations.
Hair
Animal hair incorporated into mortar can extend its life by crack control.
Straw
Straw has occasionally been incorporated into weak mortar mixes to delay its disintegration.
Shells
Shells have occasionally been seen in historic mortar. Why I don't know, perhaps from unsieved beach sand?
Granulated & Powdered Stone
These are incorporated into cement mortar to make reconstituted stone mixes, which make the mix look much more like stone.
Pigments
Pigments such as iron oxide & lamp black are sometimes incorporated to colour the mixture.
Glass Cullet
Can be incorporated.
Broken Glass
Broken glass is sometimes incorporated into concrete to make it ratproof - rats can gradually eat through concrete otherwise. This is primarily used for animal housing, where rats try to get to the food. It was also used for the hard bases of earth walls where rodents can otherwise do considerable damage to the earth walls above.
Gypsum
Gypsum is sometimes used to stabilise subsoil to make cast earth building blocks.
There's more to mortar than what you thought o'.