Diagnosing dampness faults

Case Study

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Check damp symptoms for yourself - look for these clues in the photographs

1. Can you see the original damp proof course?

Yes = it looks like a dark line and if I scrape it looks like slate or bitumen/felt. (It is most likely to be just under the air brick, if you have a timber floor, as part of the original protection of the floor joists)

No = there may not be one, or, more likely it has been covered over with soil, steps, pathways, roadways or other building alterations. This is called 'bridging' the damp proof course and will give you all the symptoms of rising damp.

Wet Walls showing green surface growth

Wet Walls showing green surface growth - Verdigris.

2. Is the damp proof course line that you can see about 6" (150mm) or more above the outside ground?

Yes = good, that is correct. This drop from the DPC to the ground is to protect against splash-up by falling rain. Check that the gutters and downpipes are in good condition and go outside in pouring rain to check that they can cope in a downpour.

No = bad. You will either need to lower the ground level or insert a new DPC at the correct height and 'tank' the walls below that new level.

Surface salting also visible - white marks

Surface salting also visible

3. Can you see fluffy white 'salts' on the wall inside, maybe pushing off the paint or wallpaper?

Yes = you have rainwater splash up or gutters overflowing. Or, under a window frame, you may not have a clean 'drip' slot. Check the exterior walls for defects, check gutters and downpipes, check the pointing in the joints, treat with Ultra Proof waterproofer.

No = your dampness may be due to 'hygroscopic salts' deposited in the wall from chimney deposits (after burning coal or wood), or from a previous use of the building (e.g. coal shed, animal food store, butchers shop). Treat with Salt Neutraliser and replaster to our 'tanking' specification using BondAcryl. In severe cases it is best to use the Mesh Membrane wall lining system, rather than 'tank' or replaster - chimney salts can burn back through even the best render backing coats sometimes.

Salting in brickwork above the DPC

Green 'verdigris' caused by rain water splash up.

Salting in brickwork above the DPC.

4. Do you have a cavity wall or a solid wall?

Yes = because you see only bricks laid along their length - no brick ends visible at any level. This type of wall should resist water penetration, because of the air gap. If it is showing damp symptoms on the inside the cavity may be blocked or the wall ties may be dirty.

No = this wall is of solid construction. You can see rows of brick 'stretchers' and then mixed rows of 'headers' and 'stretchers'. Penetrating damp or splash up rainwater can go straight through.

5. Have you got a timber floor?

Yes = look for the air bricks. Even if they are present the floor itself may have rotted and been replaced in concrete, 'bridging' the DPC and often causing rot in the skirting boards.

No = no air bricks, all concreted. Check you do not have partial solid floors, with sections of timber flooring cut off from an air supply - they will rot.

Internal view - wet skirting boards

Internal view - wet skirting boards

Can you see a water source - on the outside walls

A. Green stuff on the wall - look up - are the gutters and downpipes OK in a really heavy downpour?

B. White stuff on the wall - it indicates dampness - check window cill 'drips', roof tiles and slates, flashings and abutting structures (even stored goods against the wall).

C. Neighbours garden, road, path or garden higher than yours - water flows downhill!

D. Water leak from underground - is an area of garden or path strangely green at the height of a Summer drought?

5. Have you still got a timber floor?

Yes = find the air bricks. Even if they are present the floor itself may have rotted due to blockage or shortage of air flow. Fit new bricks to the current standard.

No = the old air bricks are still there on the outside but it is filled with concrete inside. Take them out and make good with bricks and mortar, unless they are acting as cavity wall vents or provide ventilation, via a pipe, to a remote timbered area.

Want to become Qualified in Dampness and Timber Decay?

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FURTHER READING - click to see:

Damp Proof Courses - what are they?

Damp Proofing Methods - different types.

Damp Proofing Efficacy - does it work?

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Site written by: David Moore

David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author


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