damp and decorating

[JaneV]

This might be useful!

http://www.diydoctor.org.uk/projects/da ... breast.htm

The article is extremely comprehensive. There is also the possibility of chimney salts (see towards end of article) that draws in moisture too.

[teapot]

Its a party wall ,my fireplace backs onto next doors fireplace.but they don't have any damp at all.Our chimney stack has all been pointed up ,and lead flashing checked.I just don't know where the wet is coming from .

Good information on that site, has this appeared after a rain spell?
What type of chimney cowl/pot have you got? Tricky with protected buildings as those people want to preserve even bad ideas.
A damp meter is a must and never accept a hand placed on a wall as that can only detect cold, because the moisture content of the skin is higher than a damp wall.

[salmoncottage]

Water ingress comes from the outside or from the other side, usually due to a break in the mid feathers brickwork / mortar / flashing or smoke cowl and its often exagerated by the burning of any type of fuel, but damp wood would definately produce more water vapour. Do you supply fresh cut logs for your guests for instance? if so dont! Unless its rising damp from old foundations and you say the damp is showing quite low down (damp will travel up to 3" 6' and above) so there is also that possability but the flue is far more likely to be the source.
Most damp issues are quite simple to find the source (I'm not saying cheap) but I would steer well clear of any builder who suggests ripping out a whole chimney breast before they have checked and proved to me that the above is not the source.
In the meantime, stay away from high street damp paint cures, they're expensive and wont last any time if the damp problem is not addressed. Apply 2 coats of ordinary oil based undercoat or gloss paint to the affected area and sand lightly when dry, then apply 2 coats of the room colour on top of that. If you dont have any of the room colour left then give yourself a nice change of colour on the chimney breast for the spring. This temporary fix should last through the high season and give you an opportunity to have the damp issue surveyed from the top of the chimney stack all the way down to the fire place and at a more convenient time.

[teapot]

How do you apply oil based paint on to a water damp wall? Oil based paint is used to block stains not on live wet walls

[salmoncottage]

If the wall is seriously 'wet' and not just damp then you shouldnt be looking for temporary fixes at all as you have a problem that needs looking at straight away. If its only a damp patch then oil based paint is as good a temp fix as any. Sand the area first to remove and surface powdering and slap it on thick, it will stick.

[Casscat]

If your cottage is very old and the walls are constructed of the original material, then the other cause might be hygroscopic. The finish will be breathable and allows moisture to penetrate and then to released back via evaporation. This is where our forebears had a much greater understanding of damp control than we do with our plastic, hermetically sealed obsession. If anything interferes with that breathing process then damp patches crop up. The plaster may have broken down and may simply need (sympathetic) replacement, or possibly moisture is being displaced from somewhere else. Have your neighbours had any 'improvement' works carried out lately? Have you had any replastering done?

Notwithstanding that, the chimney still seems the most likely culprit. Have you been up into the loft space? I had issues with my kitchen chimney in a previous property and once in the loft you could actually see the wetness on the brickwork.