for People with a Passion for Period Property
Ask an Agony Uncle!
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 (www.periodproperty.co.uk).

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Our experts are all specialists in matters directly involved with older properties. So, if you have a problem with an older building - or if you think you might have a problem - ask an Agony Uncle...

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SUBJECT:
Could a springy floor indicate a structural problem?
FROM:
Sarah Gooch
(Oxfordshire)

We have a springy floor in the master bedroom and we are worried about what the repair costs may be. Small amounts of plaster have started to flake round the supporting beam into the room below. We can also see a small sagging effect to the ceiling along the beam. This did follow on from moving in and heavy items being moved around the room and it does seem to be limited to one area, but we are concerned this may indicate a bigger problem. This is our first time owning a period property and we want to ensure we take good care of it.

Sarah Gooch

Springy floors are not an unusual issue with historic buildings.  In many instances it is not necessarily a problem and may not require attention.  Likewise, where floors are no longer level it is not always necessary to undertake any work.  However, in the instance you describe of pieces of plaster starting to flake from areas below, it is suggesting that there might be a gradual deterioration of the situation that might require attention.

There are a number of reasons for springiness including the fact that the floor may always have been weak and slightly springy.  However, over the years infestation and rot could have caused some damage and weakening.  Alternatively, or as well as, joists could have been weakened by notches and holes cut in them for pipes and cables.

The first thing to do is to carefully lift floorboards to examine the floor structure.  If the floorboards are old and of some value, or indeed irregularly shaped, you should label each board in sequence so that they can be laid back in precisely the same place as originally situated.  Otherwise it will be like a jigsaw puzzle without the master plan.

The upper surfaces of the structure should be checked and if you find active infestations or rot the problem needs to be resolved, perhaps by chemical treatment.  If the timbers are significantly weakened in some way it may be necessary to undertake some strengthening.  Repairs should aim to retain the timbers in situ rather than complete replacement.  It is often possible to carefully add timbers to the upper surfaces by gluing and bolting in place, or sometimes simply adding a metal structure, plates, etc., to repair or strengthen joints or certain sections.  Where there are holes or notches cut into the joists or beams these will need to be carefully infilled, assuming they are redundant.  The notches folding wedges might be appropriate.  This is where a wedge shaped piece of timber is inserted to the notch from each direction so that as they enter the notch they tighten against each other.  They should be glued in place.  If a notch or whole is still in use it might be possible to use metal plates to strengthen the area around.  If joists to beam joints are weak these can often be strengthened with metal plates and brackets.  The important thing is to try to keep the repair hidden if the joists or beams are visible from below.

Once the floor has been repaired the boarding can be reinstated.

For some floors where there is no major problem with the structure but it is springy, or where repairs have been undertaken and you want to ensure that the floor is reasonably strong once completed, you could consider laying plywood over the floor structure and screwing this into place.  This then creates a diaphragm structure, which is substantially stronger.  The boards can then be placed back on top.  The only slight problem with this approach is that it might mean changes to skirtings and doorways.

In some situations where the springiness is slight I have found that the simple action of careful screwing down of boards can stiffen the floor.  This is because the old nails have become loose over the years and by screwing the boards in place it helps to physically hold the board to the joist, therefore strengthening such junction.  However, before undertaking this you need to consider the visual appearance particularly if the existing boards are old and of some significance themselves.

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

The Whitworth Co-Partnership LLP - Chartered Architects and Surveyors

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SUBJECT:
Can we remove cement render from flint and replace with lime?
FROM:
Corinne Harper
(East Sussex)

We are in the process of buying a Grade II listed 18th century cottage. There is a significant damp (more like wet) problem which the surveyor believes to be caused mainly by cement render and non-breathable paint on the exterior walls. The ground floor is also below ground level. According to the surveyor and many articles I have read online, it may be necessary to remove the cement render and replace it with lime render. I should note that the material underneath is flint. I haven't found any case studies/examples online of where cement render has been removed from flint. My questions are:

  • how difficult is it to remove cement render?
  • if the cement render cannot be removed as the flint underneath crumbles, what is likely to be the next best option?  

I would appreciate any advice/suggestions. Also, what type of professional should I seek to advise on and complete this job?

Corinne Harper

It sounds as if your surveyor has sensibly and correctly identified a potential problem.  However, as you imply, the removal of cement render is never easy and can lead to other problems.  If the cement render is well and truly adhered to the background material, it will not come away without damaging background material or some of the cement staying in place.  However, if the render is hollow when tapped the likelihood is that it has started to de-bond anyway and may come away quite easily with minimal damage behind.  There is no way to determine how easy or difficult it might be to remove the cement render without attempting the work.  However, careful tapping of the surface should reveal how hollow it might be and therefore how easy it might be.  If you tap the surface with a short wooden stick, such as an old wooden hammer handle, it will help identify hollow areas without damaging your knuckles.

Flint is very hard and it is unlikely that the flint itself will become too damaged.  What is more likely is that the removal of the cement render will pull out the pointing or it might even pull out the whole flint.  In any event, where the cement has been causing a problem of trapped moisture there is a possibility that that moisture has caused some of the flint to loosen and you may find that some of the flint work has to be rebuilt anyway.

It is likely that around the flint is brickwork because flint is rarely used for corners.  There is more likely to be damage to the brickwork than to the flint.  The faces of the brick may crumble away and lift off with the cement.

It might be sensible to identify a small area that is relatively hidden and undertake some careful trial removal to see how easy it might be and what damage might lie beneath.

If the building is listed you will need to speak with the conservation officer about this and you may well need listed building consent.

If you find that the cement is fairly well adhered and is unlikely to come away without causing major problems, you might have to consider leaving it in place.  Although cement render is not ideal and could cause trapped moisture within the wall structure, a decision is often necessary as to whether it might cause less damage to leave it in place than by trying to remove it.

If the cement render is causing an internal damp problem but might be difficult to remove a more holistic approach may be necessary.  If the cement has to be left in place you may have to consider greatly increased ventilation internally to try to help move the moisture from the wall from the internal faces rather than from the external.

Whilst the cement render may be a cause of the damp it may not be the only one.  Once you have dealt with high ground levels and any other issues likely to be increasing the amount of moisture in the wall, you may find that even if the cement render is left in place the overall damp problem is reduced or resolved.

It seems as if your surveyor has a fairly good idea of the issues and in the first case I would suggest you return to the surveyor to see if he or she can assist you further.  For something like this you will need the assistance of a building surveyor or architect experienced in repairing historic buildings of this type.  If you are present surveyor is unable to help the conservation officer may be able to suggest the names of several surveyors or architects in the area who you could approach.

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

The Whitworth Co-Partnership LLP - Chartered Architects and Surveyors

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SUBJECT:
How do I remove layers of modern oil based waterproof paint?
FROM:
Francesca Olmi
Hertfordshire

I would appreciate any advice on how to remove layers of modern oil based waterproofing paints on top on lime wash from external Victorian brick. I would like to restore my house to the original brickwork without causing damage. There are so many paint removal systems such as TORC, DOFF, chemical removal, eco removal strippers. I would like to know which are regarded as the best methods for soft Victorian brick and which methods should be avoided.

Francesca Olmi

The removal of paints in some instances can be tricky and primarily what you need to try to do is to separate the layers.  Chemicals can remove one type of paint but leave another in place, sometimes steam or heat will do the same job and in some instances you might need to use abrasive methods.  There are also companies who would use the method of freezing the surface temporarily.

It seems you are already aware of most of the systems available. The most appropriate thing is to identify an area externally for trial removal. This should be an area that is reasonably hidden and can be used for trials without any major problems to the principal elevations. It would be sensible to identify a specialist contractor experienced in removing such surfaces from a variety of substrates and asking them to undertake the trials.

Whichever method is used there are advantages and disadvantages. Chemical removal is potentially hazardous and there is a significant issue of cleaning up as the work is undertaken and upon completion. Methods that use a lot of water can result in temporary or even permanent damp problems. Abrasive methods can physically damage the substrate.

It would be inappropriate for me to suggest that any one or more method is preferable or should be avoided without having seen the property and understood the situation directly. It is therefore best that you seek advice from someone who can visit the property and undertake trials as indicated above. When researching such companies look for those who specialise in masonry cleaning.

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

The Whitworth Co-Partnership LLP - Chartered Architects and Surveyors

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SUBJECT:
What damage requires new lime wash to be applied to walls?
FROM:
Nigel Saunders
(Dorset)

I think these are probably supplemental questions to some already covered.

I have a Shaftesbury Greenstone house, which over the years has had various paints applied to the external masonry. One wall in particular has a longstanding damp issue, which I believe is due to the paint layers trapping in the moisture. The local Conservation Officer is supportive of removing the paint though we need to agree the method and also what to do with the exposed surface.

Various methods have been tested for removing the paint including a blowtorch and four different types of chemical stripper. These are all effective to varying degrees on the surface layer (believed to be Weathershield) but underneath this is a layer of grey paint which I believe is mineral based though original brush marks are visible. I'm guessing that this is perhaps a Sandtex type product.

Given that a range of chemicals and blowtorch has no effect on the grey paint will I have to resort to an abrasive method like a needle gun or scabbler please? Also the Conservation Officer has said that Whilst the removal of non-breathable paints/covering is positive, it is unlikely that the stone will be able to remain exposed due to the damage done by the previous covering. Could you clarify what damage the coverings could have done which necessitates a new lime wash being applied please?

Nigel Saunders

Please refer to my answer above with regard to removal of paints generally.  It may be that a system that employs steam or freezing could be successful rather than an abrasive method.  You need advice from a specialist regarding the removal of the material.

Until the paint is removed it is extremely difficult to assess what damage it might have caused to the substrate.  In some instances the removal of the paint can be undertaken in such a way that the stone beneath is left sound and can be left exposed if indeed this was how it had been previously.  Until the work is undertaken it is very difficult to predict what you might find to be the end result.

Unfortunately, you are quite right in suggesting that in most instances the paints could have caused irreversible damage. If this is the case then some form of lime based finish may need to be applied. A simple limewash is the most obvious, but you might find that a slightly thicker form of lime-based slurry would be more appropriate if the damage to surfaces is more pronounced. In the extreme it might be necessary to consider applying a lime render.

With a basic lime putty there are a variety of ways it can be used. Simply watered-down it makes a lime wash but with aggregates added it makes a render. What might be most appropriate to this building is something that might only be determined once the paint has been removed. However, I would hope that a basic lime wash is all that would be required.

You ask what type of damage could have been caused and put quite simply a building that has an impermeable finish applied cannot manage moisture in the same way that can occur where permeable limewash has been applied. Therefore, moisture can become trapped within the building or indeed within the wall structure. This can lead to internal damp problems and if there are buried timbers within the wall it can cause rot or damage to the timbers. To the outer face of the building if moisture is trapped just behind the paint there can be a problem of freeze thaw action causing deterioration to the surfaces of the substrate.

There are a wide range of potential problems where impermeable finishes are applied to historic buildings. It does not always follow that an impermeable finish is causing an immediate problem and as indicated in my reply to the question above, sometimes there is less damage caused by leaving an impermeable finish them by trying to remove it. However, as this is a matter of careful judgement to be undertaken depending on the specific circumstances of that individual property. As a general rule historic buildings work best by managing the moisture and this is best achieved by impermeable finishes and therefore impermeable finishes ought to be removed and replaced.

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

The Whitworth Co-Partnership LLP - Chartered Architects and Surveyors