How does mortar work?

[Quigs]

Just sitting here and contemplating the work done on my extension by the brickies today, and was just wondering how does mortar work?!

When it is slapped on a brick for the first time it just as easily falls off - why is it then the stuff sticks rigidly when it is dry and indeed is as tough as the brick itself - I just don't understand how it sticks as it dries?!!

Not massively important but it just started to bother me before the beer kicks in ;-)

^^^^^^^^^^^^^^^^^^^^^^^^^^^ Gary Quigley See my build at

[Jim T]

I'd tell ya, but the beer will have kicked in by now, so you wouldn't comprehend my explanation! ;-)

Jim T

[L Reid]

Oh, go on Jim. I'm on wine and this has me intreagued! I take it bricks are not as smooth as they appear to be?

[Mike Halmarack]

particles, when they get wet, sprout spiders leg-like hooks which lock on to adjacent particles. Soon after that he hit me on the thumb with a claw hammer. so his credibility immediately went down in my estimation. I wouldn't believe a word, on principal.

[Mike Halmarack]

A brickie I worked with used to wipe his backside with torn pieces of cement bag. I don't think he ever used a brick though, for the very reason you mention.

[Jim T]

I'd tell you , but you spelled "intrigued" wrong, so you don't qualify... ;-)

Jim T

[zaax]

In article , Quigs writes

By hydraulic reaction (i.e. with water) it forms a solid, cohesive mass.

[Glen]

'Cos, emm......er......cos IT JUST DOES!!! OK!!

;O)

Glen

[Jim T]

If I did that, I'd shit a brick! :)

Jim T

[Michael Mcneil]

If the brick is wet enough and the mortar is the right chemistry, consistency and the weather is just right it has the ability to act as an adhesive.

The dynamic action of the mortar hitting the brick and the brick hitting the mortar, allows the cement to separate from the mix at the point of contact and enter the pores in the brick and this cement can bond back to the rest of the mortar.

The sand is there to act as an inert filler which has the effect of slowing down the chemical reaction of the cement preventing it becoming too britle in the process. The job of mortar as well as a bonding agent is to keep the bricks apaert at a distance specified for the diagonal transmission of load.

How it differs in the bonding proces from water based glues and wood is that if wetting of the wood immediately prior to applying glue takes place, it will cause the join to fail. The adhesive in that case is prevented from entering the pores in the timber because the glue and the water do not mix sufficiently.

[Brian Sharrock]

The purpose of mortar is to _keep the bricks apart_.

[Pet]

Couldn't you just use big matchsticks then like when tiling?

[Brian Sharrock]

Ok! The purpose of mortar is to _keep the bricks apart_ for a long time.

[Michael Mcneil]

Yes but using big match sticks in sufficient quantity to serve as gap filling and draught and damp exlusion is time consuming.

And sand is so much cheaper.

[zaax]

So why not make it all with concrete?

[stuart noble]

A lot to do with suction. Slap a brick on to a bed of mortar and it immediately becomes difficult to move. If you succeed in moving it more than a little, you'll have broken the suction and there will probably be no bond when the mortar is dry.

[The Natural Philosopher]

Basically, once upon a time, there were lumps of stone, and people piled them up and filled the cracks with moss, cow dung and assorted animal hair.

Then there were hot clay baked bricks, which needed less stuffing, and people found that dry sand would work, except a rampaging bull could push the wall over, and the sand washed out in the rain.

So they added lime, and it sort of held the sand together and set into something crumbly, but quite weather proof.

Then they invented cement, which totally filled the voids between the sand grains, and set hard, and modern mortar was born.

It doesn't really stick to the bricks all that well actually, but over time and dry spots get wet, and the cement sort of fills the voids in the brick face - especially after the bricks are tapped into place.

Nonetheless, take sledge to a brick wall, and its the brick to mortar joint that goes first, usually.

[The Natural Philosopher]

why not indeed?

[Dave Stanton]

O

There is also a chemical reaction going on as well as loss of water.

Dave

[NikV]

The chemical reaction is a(n?) 'Hydration' it gains water from the environment and uses it in crystal growth, binding the whole into a cohesive mass with some adhesive properties same principle as concrete (often need to supply more water in hot weather by damping)

Nik