Penetrating Damp - scot22

Help I'm mentally overloaded with trying to figure this out. How does the surveyor know definitely that the cause is penetrating damp and not another reason ? e.g sprayed the wall with water !

Penetrating Damp - daveyjp
The surveyor should identify the problem, investigate the cause, provide a solution.

Just saying a wall is wet isn’t acceptable.

I decorated a bedroom and noticed the paint wasn’t adhering well to an area below a window and suspected damp. This area was also above the front door which has a small tiled roof above.

Looked at the area and noticed the mortar holding the flashing between the roof edge and house wall had deteriorated. Scraped it out, re sealed with mastic, wall dried out.
Penetrating Damp - RobJP

In answer to the question, he'll be looking at the construction of the wall, where in the wall the damp is happening, and the area that the dampness extends to.

For example, if the damp area is present at the base of the wall and extends upwards, and the wall is a stone or rubble wall, then it'll be rising damp.

If, on the other hand, the wall is modern cavity construction (insulated or not), and the damp is in a defined area that's remote from the floor or roof, then it'll be penetrating damp. Caused by a number of things, but most likely mortar 'snots' from the construction process sitting on the wall ties OR the cavity insulation conveying moisture across the cavity.

If the construction of the wall is good - pointing in good condition, render in good condition and painted properly - then you could pour buckets of water down the outside of the wall all day long and not suffer any meaningful damp penetration.

Penetrating Damp - scot22

Thanks for the helpful responses. I am wondering about the use of the meter. When they get a high damp reading how do they know the cause ? Sprayed inside wall with a water pistol or from the outside ?

Penetrating Damp - RobJP

So, the meter measures conductivity. The more moisture, the greater the conductivity.

By taking measurements across a wall, they'll see a pattern emerge. If, for example, it's just concentrated in one finite area in the middle of the wall, and measurements tail off as you move away from that spot in all directions, then it's highly likely be penetrating damp.

If, on the other hand, measurements are highest at the bottom of the wall, and reduce as you go up the wall, then it's most likely to be rising damp.

They aren't going to be looking as to whether someone has been spraying the inside of the wall with water. Because they aren't looking for the equivalent of sabotage or vandalism.

Penetrating Damp - scot22

Thank you for coming back. It is now clear to me - much appreciated because with practical things my knowledge is limited. Pity the school system never gave a full education.

Penetrating Damp - galileo

Thank you for coming back. It is now clear to me - much appreciated because with practical things my knowledge is limited. Pity the school system never gave a full education.

There are 'moisture meters' which are calibrated and intended for use on timber: these will almost always indicate that a wall is 'damp', which is why they are a favourite tool of some surveyors who then advise various kinds of costly remedy (e.g. the installation of ceramic tubes in the wall, though these have been proved ineffective years ago.).

So when the meters probes are pressed into wood, the meter will express a quantitative reading. In effect if 12% is displayed on the meter’s display, it’s right thereabouts. It’s 12% Wood Moisture Content.

However, stick the meter is anything else; plaster, brick, stone or mortar and the reading is only qualitative – if the meter says 12% – you can discount that completely; the true moisture content of the material may be higher or lower.

This is because the meter cannot be calibrated to account for the variable nature of masonry.

Exact moisture percentage can be measured by drilling the plaster, weighing the sample, drying it by heating and then re-weighing.

NB, your surveyor may have a meter which does measure accurately, if technology has advanced in recent years.

Penetrating Damp - scot22

Thank you for adding to my knowledge.

Penetrating Damp - concrete

If you approach the surveyor and ask for more details I am sure he would be glad to explain. What has been said already is correct. If it is a solid wall construction then penetrating damp can be cured by repointing/rendering. Sometimes a severe rain storm with wind can blow against the wall and make it quite damp for some time until it evaporates. Usually this means the pointing/brickwork is porous and needs attention.

If it is a cavity wall the surveyor may possess a boroscope. He can drill through the outer leaf in the damp area, insert the boroscope and should be able to see the problem. Usually wall ties conveying moisture across the cavity to the inner leaf. Then some brickwork can be removed, the problem rectified and the bricks cemented back into place. If done carefully you would hardly notice after a few weeks. This is most likely the cause if it is a plain flat wall with no penetrations, downpipes or water services concealed in it.

Cheers Concrete

Penetrating Damp - scot22

Thanks. Does it make much difference of it is cement or lime mortar used for pointing ?

Penetrating Damp - concrete

Thanks. Does it make much difference of it is cement or lime mortar used for pointing ?

Lime mortar would be an unusual choice for standard brick construction. It is mainly used on restoration projects where older buildings are more likely to suffer movement. I would not recommend it on an exterior brick leaf of fairly modern construction and it would probably be rejected by Building Control too. Standard pointing mortar is the ideal material. Very strong and weather resistant and can me mixed with water resisting additives to help repel water. Cheers Concrete

Penetrating Damp - RobJP

Thanks. Does it make much difference of it is cement or lime mortar used for pointing ?

Lime mortar would be an unusual choice for standard brick construction. It is mainly used on restoration projects where older buildings are more likely to suffer movement. I would not recommend it on an exterior brick leaf of fairly modern construction and it would probably be rejected by Building Control too. Standard pointing mortar is the ideal material. Very strong and weather resistant and can me mixed with water resisting additives to help repel water. Cheers Concrete

Alternatively, if it's an old building, then the stonework needs to be able to 'breathe',which lime mortar is ideal for. Modern cement mortars are very impervious in comparison.

Penetrating Damp - scot22

Sorry. Should have said it's Victorian stone building.

Penetrating Damp - RobJP

Sorry. Should have said it's Victorian stone building.

So, no cavity. Solid wall construction of some sort. The mortar could be of either type - lime or cement based.

But if the stonework and pointing looks good from the outside - say from a binoculars - then the damp is coming in through some other line. Bear in mind that if (for example) the lead flashing at roof level was not intact, and water was entering the fabric of the building at that point, then the water could 'track' through the fabric of the building until it reaches the internal surface some distance away and becomes visible.

Penetrating Damp - FP

"...the water could 'track' through the fabric of the building until it reaches the internal surface some distance away and becomes visible."

That last bit is important - the external point of water penetration could be a long way from where you're aware of it.

Penetrating Damp - Falkirk Bairn

A really serious damp problem.

www.telegraph.co.uk/news/2017/12/06/mackint***s-hill-house-enclosed-giant-cage-part-major-conservation/

People come from all over the world to see Hill House & it is danger of crumbling away - it's getting a tent to help dry it out.

Penetrating Damp - scot22

These posts are very valuable for me. It is a complicated situation outside what you would look for on a forum. Historical, legal and personal issues. I appreciate that posters have given me knowledge on this particular aspects. Many thanks all.

Penetrating Damp - galileo

We lived for years in a Victorian (built 1881) house which had lead-lined stone roof gutters: we had recurring damp problems, finally cured by having one-piece extruded aluminium liners installed in the gutters. (We had similar liners installed in our current 1960's house which was built with concrete roof. gutters).

Penetrating Damp - FP

"We had similar liners installed in our current 1960's house which was built with concrete roof gutters."

Oh, that reminds me of a house I once was involved with - a major renovation. Concrete gutters - the spawn of the devil. What a stupid (and thankfully short-lived) feature of fifties and sixties construction. Some of them were even partially supported by top-floor window frames, so replacing windows could run into serious problems.

There are specialist firms that remove them (expensive, involving scaffolding and reconstruction of the lower roof), but extruded liners (cheaper, but not cheap) are the best solution.

Edited by FP on 08/12/2017 at 14:35

Penetrating Damp - concrete

Victorian construction indicates that the walls would be soild brick construction. Probably at least 9" or 14" thick. Water driven at these walls by wind will eventually penetrate after a while, but that would be unusual in all but extreme conditions. The pointing and decent bricks(i.e dense witha good resistance to permeability) should do the job of keeping the rain out. The building will 'breathe' as a natural process when the air temperature and the dry wind will assist it to evaporate moisture from the brickwork. Water ingress from elsewhere, i.e. gutters, downcomers, spalled roof tiles/slates near the soffit and facia, will of course only be present after or during a rainstorm. Water can track and always takes the easiest line of resistance which can bring it to the surface of the interior side of the wall. This needs a thorough examination to determine the point of entry. Old buildings are fine and we enjoyed living in ours for over 35 years, but they do need regular maintainance and attention. Usually if a problem is identified and rectified with good modern materials and good workmanship the buildings will go on and on being nice to live in.

Cheers Concrete

Penetrating Damp - scot22

Thanks again, you're a star. Before long I might start to know what I'm talking about.

 

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