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Stephen Boniface - Stephen Boniface specialises in building conservation providing multi-disciplinary consulting services. He is Chairman of the Building Surveying Faculty and member of the Residential faculty. He serves on the RICS Building Conservation Forum Board and is the 'Agony Uncle' on the Period Property UK website (

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SUBJECT: Leaky chimney drives us to tears.
FROM: Jane Smith (Yorkshire)
We have a leaking chimney which is causing us a lot of problems

Our house is Victorian and older, and is in a very exposed moorland location near Sheffield. A chimney at the north end of the house leaks terribly. The stack is made of millstone grit. Over the six years since we moved in, we have had the flashing replaced; had it repointed; had the pots and concrete flaunching replaced; and had the stack painted with sealant and water repellant. This last was done about a year ago. The chimney dried out over the summer but is now leaking again. When it is really bad, water pours down the inside walls. It often waits until after the rain has stopped to start leaking, as if the chimney is soaking up the water like a sponge then releasing it later.

We don't want to remove the chimney as it would spoil the look of the house, and even if we wanted to, the planners would probably stop us. Rebuilding it would be difficult as we can't find matching stone. We have been advised to render it but this would also spoil the look of the house.

Jane Smith

Modern chimneys and some older chimneys are constructed with horizontal damp proof courses at high level and this helps prevent the problem you describe. However, it is often unrealistic to reconstruct older chimneys with damp proof courses within them unless there is a very serious problem that cannot be resolved in any other way.

You do not say whether you use the chimney and if so what type of heater, fire or other appliance is utilising the chimney flue. This could have an influence because traditionally a chimney in use would tend to be dried out by the fire itself.

The obvious problems seem to have been dealt with, i.e. flashings and flaunchings. I am not convinced that painting the surfaces of the stack with a sealant and water repellent have done any good, but neither are they likely to have exacerbated the problem.

You do not say precisely what sort of damage is being caused other than that water runs down the chimney. Are there stains to the chimneybreast faces and therefore through plasterwork etc or is it simply that water is dripping down into the fireplaces? The fact that you suggest you have problems indicate that it is causing unwanted damage to plaster and decorative finishes but I would need further information on this before giving definitive advice.

It is quite normal for water to drip down the flue of a disused chimney. The fact that some chimneys would not be completely vertical shafts means that the water dripping down will hit surfaces etc and there is a risk of that water then permeating through to surfaces internally. As mentioned above, use of the chimney by a genuine fire will often help dry out the chimney and prevent this happening.

Without further information it is difficult to provide definitive advice but it sounds to me as if the insertion of some form of capping to the chimneypots might resolve the problem. It is possible to obtain flue terminals formed of terracotta that simply slot into the chimneypots. These have the effect of preventing direct rainwater penetration but permitting ventilation. It might be sensible to have these installed to start with to see if they resolve the problem. If they do not they are easily removed. If they do and you wish to use the flues for any form of fire etc then a suitable flue terminal that prevents direct water penetration when the fire is not in use would have to be considered. Advice from a specialist would need to be sought on such matters.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.



SUBJECT: Re-instate internal render to hide & protect flaky bricks
FROM: Caroline Richardson (Essex)
We have an entire wall in the sitting room of our 1850's cottage of exposed original soft red brick with the fireplace set in the middle of it. The wall has been unsympathetically overhauled at some point with bricks very sharply faced off and all repointing done with a cement mix (dark grey in colour). Some of the bricks are also flaking quite badly. The 2 questions we have are - is there any kind of "lime wash" we could apply to the wall to tone down the rather overpowering effect of the bricks and make them appear softer and is there any solution we should apply to halt the flaking of the bricks ?

Caroline Richardson

The fact that some of the bricks are flaking suggests that there is moisture trapped within the wall (or penetrating through somehow) and because the pointing is too dense the moisture can only escape through the brick faces, hence causing the damage. My first suggestion is that the cement pointing should be raked out.

I doubt if the wall was originally intended to be exposed and although raking out the cement mortar could cause damage to the brickwork, because it will be covered by plaster in due course I would not regard this as too much of a problem.

Once the cement has been removed the wall should begin to dry out. There are many other answers to agony uncle questions and postings on the discussion forum regarding dampness generally in walls. I would refer you to these.

The wall should be re-pointed using a lime mortar so that it can breathe properly. Once this has been dealt with you can then decide how to finish the wall. If you wish to leave the bricks exposed but have them coated in some way then using a lime wash is a possible solution to the problem. However, I suspect that the wall was originally intended to be plastered in which case I would suggest that you use a traditional lime plaster system. If there is a build up of salt within the wall the plaster system might have to be regarded as sacrificial for the first year or so until salts have come out of the wall and the lime plaster should then have a normal effective life.

I would not recommend applying any sealing solution on the bricks as this could accelerate the problem.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.



SUBJECT: Trampolining kids cause ceiling problems
FROM: William O'Brien (Fincham, Norfolk)
I have young children whose trampolining skills have caused a major sag in the lath and plaster ceiling below their bedroom. For the moment I have propped the ceiling back in place but it is quite badly cracked. I propose to try and screw the plaster back to the joists but also recall reading somewhere that extensive use of plaster of paris and hessian is useful in helping to re-secure the plaster to the lath. I suspect the screws alone may not suffice but am sceptical about using plaster of paris to reattach to the back of the laths. Am I right to be sceptical?

William O'Brien

My first suggestion is that you provide a trampoline somewhere on the ground floor of the building to discourage them from using the bedrooms.

How a lath and plaster ceiling is repaired will depend upon precisely what damage has occurred. It is quite likely that you have a combination of problems and you might need to combine not only screwing the plaster back through to joists (using long threaded screws and metal mesh washers) but also reinforcing the ceiling from above by reforming the key above the laths. You have correctly heard that a method is to use hessian and plaster of paris. The method is detailed in the English Heritage books "practical building conservation" specifically volume 3. Quite simply it involves installing hessian secured to the joists either side of the area being repaired to form a reinforcing layer. Once the upper surface of the ceiling has been cleaned and prepared Plaster-of-Paris is carefully poured over the area. Once set any propping etc can be removed and the ceiling should then stay in place. The method is long established and has been proven successful in some instances but there is no guarantee that it will always be successful. Other methods have involved the use of resins and different materials. However, I would be reluctant to use anything other than a traditional material. Nonetheless, the principal remains that to reinstate the ceiling does involve trying to secure the back of the original ceiling up and over the laths to reform the key.

If the ceiling is without any ornament and is relatively flat and not in itself of particular aesthetic or other historic merit you could consider over boarding with plasterboard. This would involve screwing plasterboard through the existing plaster to the joists above and then skimming over. It does not have the same finished appearance as traditional lath and plaster and I tend to use it only on relatively plain and "unimportant" Victorian or later buildings. A thought occurs to me that it might be possible to secure expanded metal lath across the ceiling using long screws to hold it through to the joists above and then to skim over with a lime plaster. This is probably more sympathetic than using plasterboard but the same principal applies in that you are creating a new surface secured through the existing ceiling.

If there are any areas of the lath and plaster that have deteriorated so badly that they need to be reformed I would recommend using traditional materials etc. However, when removing the old plaster it is necessary to carefully cut around the area to be removed, in order to avoid loosening otherwise sound sections beyond the damaged area.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.


SUBJECT: Cellar conversion advice
FROM: David Ilbert (Stockport, Cheshire)
The overall decision to use a particular company for cellar conversion was based on the many readings I had picked up on the Breathability of the walls. A sump and pump seems to be the most obvious but how much does it cost to keep the battery going on a yearly basis. I have thought of excavating 6ft of Garden away from the back wall to extend the basement area and eliminate a need for any type of tanking on this wall. This is an area I am very keen on as we have plenty of garden space. However am I now back to the same problem with a wall that would then be supporting the depth of the garden which is almost 7ft? Obviously a drain is needed but what is the most long lasting constitution of a wall in this case e.g. What type of stone or brick is best?

David Ilbert

I am not sure why you think that the pump will be a battery driven unit. In my experience the pump would be served by mains power and can even have an alarm should failure occur etc. I do not have figures for the likely running costs but I am sure that pump manufacturers can provide this.

Your second point is about removing some of the earth to create a gap between the basement and the surrounding garden. What you would need to do is to build a retaining wall. There are many different methods of building retaining walls including stone, brickwork, timber, concrete or even steel sheets. It would be sensible to get a local engineer to discuss this with you and design the retaining wall itself. Whatever form the wall takes it should have drainage so that moisture getting into the soil can drain through the retaining wall. It would mean that the area formed by the basement within itself would have to be drained, probably by a soak away.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.



SUBJECT: Advice needed to build doorway in cob cottage.
FROM: Kim Chadwick (St Austell, Cornwall)
We are purchasing a 200 year old Cob Cottage. Can you help point us in the right direction on advice on knocking a hole in the External Cobb Wall? can it be done, are there any special factors to consider with Cob? We would like advice on how to work with Cob.

Kim Chadwick

I note that the property you refer to is 200 years old and if it is listed you will need to obtain listed buildings consent for any new openings or alterations to the structure. Assuming that consent is properly obtained it should be relatively straight forward to form an opening in a cob wall. The first thing to do would be to carefully cut through and install a lintel at the head of the new opening position. The lintel should be at least 100mm wider to each side with a bearing of at least 100mm. The size of the lintel, its depth etc will be determined by the opening itself and what lies above the opening. You might need to seek advice from the engineer on the precise nature of the lintel etc. Once the lintel has been installed the opening below can be carefully cut out and the cob removed to form the opening itself whereupon the frame linings etc for the window or door can be inserted. For further advice I would refer you to the following website where information can be obtained on such matters You could also look at and follow the link to guidance where there is a paper on earth structures.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.


SUBJECT: Clicking noises in friends' house leads to concerns.
FROM: Lilibet Taylor (Hernhill, Kent)
At night a dull clicking noise can be heard coming from a beam in a friends 17thc timber framed house. Is this live woodworm or what is it likely to be and what is the best treatment?

Lilibet Taylor

Assuming that the frame you refer to is of Oak or a hardwood the noise you refer to is probably deathwatch beetle. Quite often the infestation will be in sections of the building that are difficult to access. The beetle will usually be found in the sapwood of oak or in areas where the oak has started to rot. It can sometimes be very difficult to find the precise location of the infestation. However, it is imperative that the site of the infestation be found in order to ensure that any treatment is fully effective. Simple generalised surface treatment is unlikely to have much effect if any at all. The treatment should be targeted. The recently published guide by the Building Research Establishment suggests that appropriate treatment would involve organic solvent, micro emulsion or paste to those timbers and areas affected. However, it makes it quite clear that it is imperative that measures be taken to reduce dampness as most infestations will usually be associated with a damp problem.

With deathwatch beetle there is a possibility that the core of the timber will be hollowed out and therefore where possible the centre of a beam or timber member should be checked and also treated where possible.

If you refer to the discussion forum of this site there are a number of other queries and pieces of information relating to deathwatch beetle infestation and treatment.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.



SUBJECT: Cement render on rubble walls leads to damp problems
FROM: Tony McNicholl (Holyhead, Gwynedd County)
My house was built in 1894; the walls are 24-inch thick rubble-stone with a very hard cementitious render. There is not a dpc. I have a number of damp problems, some probably penetrating damp and others possibly rising damp, and would like to know who to consult to get a reliable diagnosis, which is not biased by a connection with a particular product or company. Is there are a directory of such consultants, or what sort of qualification should I expect a 'damp consultant' to have?

Tony McNicholl

The hard cementitous render of the faces of the wall will simply serve to trap any moisture within the building. Until this is removed and moisture trapped within the building is released it will be difficult to know whether you have a genuine rising damp or other problem. It is quite possible that the building was always intended to be rendered, but traditionally this would have been a lime render. It is the cementitous render and its impermeable nature that generally causes the problem of dampness in this type of property. I therefore suggest that you do not need to consult any specialist at present until such time as the render has been removed (by a careful builder who understands this type of building and problem) and perhaps the walls re-rendered with a lime render. Over time the walls should dry out and some of your problems disappear. If they do not disappear entirely further investigation might be necessary. You will note that on the website discussion forum there are a number of postings from Graham Coleman of Remedial Technical Services. I suggest you look at his website I believe he is an independent consultant who could give the advice you require or he may know of someone more local to you who can advise appropriately.


Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.



SUBJECT: Should disused chimney flues be vented?
FROM: Ross Easton (Denny, Central Scotland)
Two years ago my partner and I purchased a Sandstone Detached Home. The property has fireplaces in all 4 bedrooms upstairs and all 4 public rooms downstairs only one of which is unfortunately still in use. All the rest are bricked up, but have no venting. I have been advised to put in venting, but as there is no sign of dampness in any of the rooms do I need to?

Ross Easton

My general advice is always that disused chimney flues ought to be vented.

Behind boarded or blocked up fireplaces there is often a build up of debris, soot, etc. Over time this could become damp either through condensation or perhaps even by direct water penetration from above (rain) and in due course damp problems could occur. It is for these reasons that I always favour ventilating disused chimney flues. However, it does occur to me that you could actually remove the bricking up and re-establish the fireplaces either to bring them back into use or simply to have them as aesthetic features in the rooms. It is possible to obtain something called a chimney balloon that can be put up into the base of the flue void (just above the visible fireplace opening) that can be pumped up to inflate and therefore reduce the number of drafts etc through the fireplace whilst at the same time allowing some ventilation. It can easily be deflated if the fire is to be used or in the summer when you might want the fresh air and draught flowing through.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at the The Whitworth Co-Partnership with Boniface Associates for responding to this question.