Right I am assuming you know zilch about mortar so sorry if I am telling you how to suck eggs. Mortar is the “glue” THAT STICKS ONE BRICK OR STONE TO ANOTHER.
So you are thinking this will be a short blog because there is not a lot more you can have up your sleeve on this topic.
Sorry again, there is a Linked in drama on this!
There are two types of mortar and it is REALLY important you use the right one for the right job.
Here comes the history lesson. For 4000 years the best way to stick bricks (dried clay rectangles) together was using a mixture of lime(crushed old seashells), aggregate (sand and small stones) and water. It was so good that nobody thought to improve on it in the next 3900 years.
Post WWII there was a rush to literally rebuild Europe. This must have disrupted the seashell economy or something but an alternative was found - concrete. It had nothing to do with seashell economies actually - it was all to do with time. Lime mortar needs time to go off, and so this slows down the speed and height that can be laid in a day. Concrete mortar is easier to use, quick setting and has a higher compressive strength. In fact concrete started to turn up everywhere because those clay rectangles (bricks) stopped being made of clay and started to be made of concrete with a bit of colour added to make them look like the old ones. These new bricks didn’t need drying or cooking in a kiln so they could be made lots faster and time is money.
So everything became a bit mix and match during the 1940’s to present day. Except people in the know started to realise that mixing and matching is not a good idea at all. Bricks and stone started to flake and crumble. Damp became a problem and buildings started to fall apart. So why was this starting to happen, and especially in repaired, altered or extended older properties?
Concrete is not porous (it doesn’t allow the passage of water) Which is good - yes? Well yes but if you use it with other products that are porous they trap water. Tada...perfect conditions for damp and mould. Everything is fine when it is all porous as in the old buildings with lime mortar and clay bricks the water wicks to the surface and dries out. All is fine if you use all concrete non-porous materials as they shed the moisture. You start repointing, rendering and mixing lime mortar and concrete mortar and the problems start.
So if you are using old reclaimed bricks - use lime mortar. If you are unsure...
We are pretty good at solving brick problems, so are reputable Stonemasons, Conservation Accredited Building Surveyors, builders experienced in renovations, lime mortar manufacturers. A bit of homework and asking around and you will have the job half done before you even lift the trowel.