Hi, In a house that has a chimney with an unused open fireplace on gnd floor and 2 vents upstairs. There is a damp patch on the chimney breast is this condensation or damp?

This is a common problem with late 1800's builds. these properties were built to "breath" and are reliant on an even percentage of water ingress and exhaust which is why a chimney is so important to be used in this type of property. Using cement based products is your cause of your problem. The alternative method to keeping the property breathing properly is to ONLY use breathable material IE lime plaster/bonding and breathable paints. keeping your chimney open is also a great benefit as your heating will allow moisture to exhaust through it. With regard to the continual water ingress i will assume this is through your chimney itself. In many cases, rain penetration is caused by poorly designed or maintained building details (e.g. blocked down pipes or leaking gutters and age related masonry damage) causing large amounts of rainwater to flow over a small section of masonry. In these cases, the penetrating damp can usually be cured by rectifying the defect. In other cases rain penetration can be caused by the masonry wall not being weather tight enough to withstand local weather conditions. Often the weather tightness of the masonry can be improved using external render, cladding, or weatherproof paints. However these solutions all change the visual appearance of the masonry. The alternative is to use a weather proof clear paint and can be applied to all masonry to try and cure too much water ingress. This is a suitable solution to use without having to change the appearance of your property. There is allot involved in regard to this but please feel free to contact us if you would like us to send you are full guidance pack for free in regard to this. As this is something we advise on regularly. Kind Regards Peter Phoenix UK Renovations Ltd

without looking at the problem it is impossible to say what is causing this dampness, it could be many differant issues. post it in the dampness section on the site and get a local expert round to diagnoise the cause and cost

Difficult to say without some investigation. The fact that you have vents in the upstairs rooms is good, this should prevent condensation build up. Is the damp patch on the breast in bedroom or downstairs? Could be incorrectly terminated flues, could be nesting material which has been in there for a long time. After years it turns to compost and will leach through the brickwork. Martyn Heywood, Chimney Care & Repair

With regard to the first answer by Phoenix all in the first paragraph is correct. Unfortunately If you, paint, render or try to seal old brick and lime you will trap moisture🙁 If the chimney has been capped with a paving slab there maybe water getting in at some point there or through a hole in the mortar that then runs down the inside settling on old debris or the " turn" in the chimney. If it's open get it swept and then check the mortar and the flashing at the roof/tile line. Most chimneys leak there. You can use cherry picker, scaffold, or drone or if you know what your doing a roof ladder.