Rising Damp is Capillary Action

[bobasd]

Rising Damp is Capillary Action by another name.

Penetrating Damp is often Capillary Action by another name.

Moisture is absorbed by Capillary Action into sponges, and paper towels, and bricks and mortar.

Where it affects masonry we usually call it Rising Damp.

To deny Rising Damp is to deny Capillary Action.

 

[JohnD]

but clean brickwork, with cement mortar, it will often only climb a couple of courses. I understand this is due to the different pore size in the brick and in the mortar which block the capillarity from climbing further. I expect you've seen photos of laboratory experiments and old bridges where well-built brick piers stand in tanks of water. The water quickly soaks into the first brick, but is obstructed by the mortar joint.

Plaster, render, soil, salts impregnation and random rubble can help it climb further. In a well-ventilated UK floor void, it will seldom reach the DPC because it soon reaches the height where evaporation (drying out) matches the rate at which new water is absorbed.

The water has to come from somewhere, and in an ordinary UK house it is very often a leaking pipe or a broken drain. Which has to be found and repaired.

 

[^woody^]

OMG. It was a nice quiet relaxing Sunday night, and then BAM! you hit us with this revelation?

And in monolithic sentences to boot.

Well, I am shocked. Shocked I tell you.

Where is Softus when you need him? Softusjuice, Softusjuice, Softusjuice.

 

[bobasd]

as the name diynot implies, there are diy'ers on this site. diy'ers who dont know the simple realities, and often
believe the myths such as the foolish, but well publicised, "rising damp doesn't exist" remarks by the president of the RICS some years ago.

there are also long time contributors & rising damp deniers such as foxhole - see his
post # 15 on thread "Advice on stripping back to brick with damp walls" last friday.

foxhole claimed the OP "doesn't have rising damp, no one does."

 

[JohnD]

What do you say this is?

 

[Leofric]

What do you say this is?

God knows, has somebody painted the bottom course of bricks dark red

 

[JohnD]

no, the bottom course is darker because it is wet because it is in contact with water in the tray.

The upper courses aren't, and aren't, and aren't.

Is that picture one you have not seen before?

 

[Leofric]

no, the bottom course is darker because it is wet because it is in contact with water in the tray.

Did you think I was being serious , but seriously are you suggesting that is conclusive proof that dpc's are not necessary as a precaution against rising damp

 

[JohnD]

no

but I am suggesting that good clean brickwork with cement mortar is not very absorbent.

Often the fault is due to something else, that needs correcting.

 

[Leofric]

but I am suggesting that good clean brickwork with cement mortar is not very absorbent.

Obviously depends on the type of brickwork , but I would stick with the use of dpc's.

Often the fault is due to something else, that needs correcting.

There obviously may be other causes of damp if pipes or the roof are leaking but I don't believe you can rely on rising damp stopping at one course of brick as the photo suggests.

 

[^woody^]

but I am suggesting that good clean brickwork with cement mortar is not very absorbent.

Then why do we have things like engineering bricks, or bricks made from specific clays, or fired for specific times, so as to increase their water resistance?

 

[JohnD]

because they're even better? But many houses without them are not damp. I do approve of building techniques to prevent damp, of course.

but what I have in mind is that "rising damp" in an old building very often has a cause that is a defect, such as a leak or DPC bridging, or blocked airbricks, and addressing this cause is both necessary and helpful in curing the damp. The former chief of RICS, if I recall, says he used his "Rising Damp Does Not Exist" statement as a headline to his talk or paper in which he went on to talk about more likely causes, and particularly, the fact that chemical injections do not repair building faults that may be the true cause.

The pictures of experiments with brick piers standing in water are very striking.

 

[bernardgreen]

The evidence is flawed

A good read HERE with references to Jeff Howell

He spoke to the BRE (generally considered to be the authority on this sort of thing) and they advised they had had similar problems with their brick peers and they hadn't had any success until they used a more absorbent brick and a chalk based mortar mix (the sort that we never use in construction). Only in these circumstances would water draw up through the brickwork.

So we now have the very strange situation where the test for rising damp is actually different to the reality, or maybe it isn't a strange situation!

 

[JP_]

And in a wall with nothing but bricks and no leaks from above, why does it get damp?

I am no expert, but have read the whole rising damp debate thing, and came to the conclusion that not all walls are the same.

The height of rise of water in a capillary (h) is governed by the following equation:

Where γ = surface tension, θ = contact angle, r = capillary radius, ρ = liquid density and g = gravity.

The equation describes the relationship between pore size and height of rise. In the case of water, it has been found that when the pore size is 0.1 mm then the rise is 14 cm but when the size is 0.01 mm the rise can be 1.4 m. The pore size in bricks and mortar can be as small as 0.001 mm so there significant potential for rising damp [4]. Water rises in the structure of porous building materials through the process of capillarity. Further considerations are the rate of transport, which is influenced by the pore structure and viscous forces (see for example [5]), and subsequent removal by evaporation.

Evaporation is an important factor in rising damp. The surface of an affected wall contains moisture that has risen from the ground and this moisture is then subject to evaporation.

Source: https://www.safeguardeurope.com/papers-articles/rising-damp-in-masonry-walls
​

In the picture above of the bricks in water, it's probably a combination of larger pores reducing the rate the water can "climb"., new bricks not holding any salts, and ventilation drying them out. In a wall covered in render and plaster, the air flow does not exist (unless there's a cavity that isn't stuffed with insulation) so again, bricks will drier faster than capillary action occurs.

Salts play a big role in rising damp too, which is why it gets worse over time rather than just all appearing after the first wet weather:

In addition, the rising water can dissolve and redistribute the salts in the bricks and mortar allowing high concentrations of salt to build up. The consequences of the salt build-up are that;

(a) The salts can block the pores and capillaries through which the water evaporates and thereby push the rising damp front higher as also demonstrated in the above equation [9].

(b) Moisture content is increased in the mortar from the hygroscopic nature of the salts with the possibility of attracting further moisture into the wall. This contribution would be relatively small in comparison with capillary moisture.
(same source)​

I guess if you're building a new wall you can either examine all the materials under a microscope to check that they are optimally manufactured to resist rising damp, or just chuck in a damp course.

 

[JohnD]

And in a wall with nothing but bricks and no leaks from above, why does it get damp?

It rises in a plain brick wall, but its rise is limited. The mortar joints in the bricks impede the rise.

Render and plaster aid capillarity.

I'm all in favour of DPCs.