tiny round damp spots

Postby ajdunny » Wed Oct 10, 2007 8:52 am

We moved into our 1904 house 8 weeks ago. The survey flagged up some highish readings at ground floor level but it's upstairs where we have discovered some very small circular spots on the paintwork in certain areas (all on the inside of external walls.).

They appeared about two weeks ago but don't seem to spreading. The areas affected measure only about half a square metre. Is this just old damp patches showing through a freshly painted wall.

It also seems that if you catch the spots early enough they sometimes just rub off. Any ideas.
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Postby camel_face69 » Tue Oct 16, 2007 3:43 pm

Hi sorry to hijack your thread but...I too have the same/similar problem.

Its on the inside of an upstairs wall (which is an external wall). The room was plastered around 2 years ago and now in a few areas the paintwork goes a slightly darker colour then the paint blisters in small circles and eventually flakes off. There are 2 patches on the wall.

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Postby LCL » Tue Oct 16, 2007 5:53 pm


What colour are the spots and are they 1/2 sqm each or combined?
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Postby ajdunny » Thu Oct 18, 2007 12:35 pm

The spots are less than size of a 5p piece. It just looks like someone has used a sprinkler head to spray the wall with water.
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Postby baffledofbristol » Thu May 03, 2012 8:55 am

Hi Ajdunny,

I know it's been a very long time, but can you remember what the issue was with the tiny round damp spots, and whether you managed to resolve it.
We have exactly the same thing as you described - in a Victorian terrace - inside back upstairs bedroom, which has an external wall, and looks likes someone has sprayed water on the wall. It seems to be in the middle of the wall - not at top or bottom.
Any advice would be appreciated ! Thanks.
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Postby Refresh PSC » Sun May 06, 2012 12:15 pm

I'm obviously posting blind with this thread as I can't physically see the symptoms you're experiencing but I'll tell you what I'd normally check with these signs. It may help you locate the problem.

The following checklist is based on you saying the problem was on an external facing upstairs bedroom so we can rule out rising dampness;

1. Check the pointing. Missing mortar will provide a route for any ingressing moisture which will then dissipate and pop up in sporadic areas on internal plasterwork.
(Also as a footnote to this point, if the mortar is a lime mortar which is highly absorbent, it can track through to your internal side of the wall. If the internal plaster is also lime based (Original plaster) this can easily become damp without any visible signs of ingress point.) Theoretically, you will have an absorbent passage for moisture tracking in from outside.
If the mortar is lime based, leave it as is but if the internal plaster is lime based, replace it with a waterproof sand and cement render.

2. The location and condition of your guttering downpipe and the type of brackets holding it onto the wall can sometimes be a problem. If it is in the local area of the damp problem, check to see if it is made from plastic or cast iron. Cast iron pipe brackets screw deep into the masonry and as such can provide a route for any rainwater hitting that external wall.

3. If you have a loft expansion tank, check it and its associated pipework for any leaks that may be feeding onto that wall. You'll be surprised on how many times I've found a leaking loft tank causing upstairs dampness.

4. Guttering, fascia boards, faulty, missing tiles and any flashing that are allowing rainwater passage into the wall.

You'll normally find that if none of the above points are relevant, re-plastering incorporating a waterproof chemical such as Sika 1 will normally do the trick. I do not advise sealing the external face of walls unless absolutely necessary as brickwork is designed to breathe on the external face allowing natural evaporation of residual moisture.

Hope this helps.
Refresh PSC
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Postby ajdunny » Fri May 11, 2012 1:33 pm

Hi baffledofbristol,
Every professional person who saw the spots agreed that they were caused by condensation. We have improved the loft ventillation with ridge vents and soffit vents, (it was very wet at times up there)
We are also using a dehumidifier which seems to help. With respect to washing off the spots we have used a mould spray and are waiting to see if the problem recurs before using something stronger.

Let me know how you get on as it may be a while before we can say for certain that we have solved it.
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Postby baffledofbristol » Fri May 11, 2012 5:01 pm

Thank you Refresh PSC and Ajdunny for your helpful replies.

I'm really hoping it's condensation as as any work to the external wall (eg, repairing cracked render) would require scaffolding in next door's garden. (Also as its a terrace, access is through the house for transfer of building materials & waste - not ideal).

I've bitten the bullet and have a professional damp surveyor coming over in a couple of weeks time, so I'll update this thread when I get his opinion.
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Postby ajdunny » Fri May 11, 2012 9:54 pm

It'll be good to hear from you once you've had your survey. Is it an independent survey? Be careful if they quote for the work as they may quote for what they want to do rather than what actually needs doing. Worth getting a few different opinions.
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Postby laorc » Sat May 12, 2012 7:33 am

I had a similar problem with black spots of mould around my windows and abit in the bays at the front of my house. I thought it might have been damp coming in so i got a surveyor on from a company and they confirmed it to be condensation. it was a relief to find this out as i didnt want to be hacking off plaster in the lounge as i had just redecorated it. This firm put a system in and it seems to have helped with the problem and its kept away so far.
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Postby ajdunny » Sat May 12, 2012 8:33 am

Thanks for that. What sort of system was it?
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Postby baffledofbristol » Fri May 25, 2012 2:26 pm

Independent damp surveyor came this week and said it is definitely condensation caused by the cold North facing wall meeting the warmer air inside. He measured the humidity of the wall and it was completely dry.
(Incidentally, found out after that the neighbour has exactly the same problem on the equivalent wall, so maybe there are rows and rows of Victorian terraces with the same problem!).

Solutions were as follows :
- insulate the wall from inside (we didn't have room to do this, so he suggested using an insulated lining paper, which might help);
- fit a battled air vent to improve air ventilation;
- move furniture away from the affected wall to improve air flow;
- keep room ventilated as much as possible by opening window and keeping the trickle vent at the top of the uPVC double glazed window.

Hope it works !
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