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 'Non-destructive surveys' -- The expectations?

Almost all the surveys/inspections undertaken by specialist damp and timber companies involve 'non-destructive' evaluations; it is currently standard industry practice.

What do we mean by 'non-destructive'?

destruc1Basically, one cannot cause damage to the decorations, fixings, fittings and the property in general. So, for Destructive 1example, whilst one may be able to readily lift carpets and square edge floor boards and re-fix, the same cannot be said in relation to lifting fitted carpets (perhaps), cutting T and G boards, removing skirtings, wallpaper, plaster, etc. - these effectively are 'destructive' and likely to cause damage. Such acts are very unlikely to be allowed in a vendor's property and in most owner occupied houses. Furthermore, once a destructive investigation is undertaken it will require considerably more time, effort and facilities than the standard non-destructive survey - and a considerably different report.



What then can a client expect for a 'free' or low cost survey, i.e., like that traditionally undertaken in the remedial treatment industry?

destruc2They should expect a level of expertise commensurate with that of a specialist surveyor. For example, a surveyor may observe blocked air bricks serving a timber suspended floor but he cannot lift floorboards. What he must do is put the client on notice because of the potential presence of rot in the subfloor timbers due to lack of ventilation. He might get even more data by the proper use of hammer electrodes in the floorboards.

Similarly, if he sees evidence of, say, a long term overflowing gutter then even if he cannot specifically see internal dampness or obtain moisture meter readings internally to suggest dampness then he must advise the client that timbers in this area which he cannot access could be at risk to rot, possibly even rotted - there might be damp within the wall. This is the expertise of a competent specialist surveyor using his skill and knowledge to advise of potential problems on evidence obtained from a non-destructive inspection.

But when it comes to evaluating rising dampness, for example, using non-destructive tests, e.g., electrical moisture meters, what then?

First consider that an electrical moisture meter will effectively respond to any electrically conducting substrate (it is 'qualitative'). In over 95% of cases this means water and/or hygroscopic salts. In many cases the pattern of readings from from an electrical moisture meter from salts alone could be similar to those resulting from active rising damp, i.e., high readings at the base of the wall with a sudden cut off higher up.

So is it possible for the surveyor using non-destructive techniques to identify a 'salt' problem alone from active rising damp? In most cases, probably not!

Would it therefore be reasonable for the client to expect this distinction to be made by the surveyor using normal non-destructive investigation techniques - again, in my opinion, probably no. (Please note: on-site testing using salts kits, carbide meters, etc. can be unreliable, again being solely dependent on the skill and expertise of the on-site investigator, and his ability to interpret the usually very limited data obtained on-site.)

'Yer get owt for nowt!

Where such situations occur with reference to a salt alone problem, and they are usually rare, should the client reasonably expect destructive investigations as part of a 'free' or low-cost investigation? Quite simply, no.

mprofileIn the above case, to undertake a 'destructive' investigation properly, full moisture and salt profiles will beProfile needed. These involve analytical techniques and usually laboratory facilities. So such investigations will clearly take time and specialist facilities, often with fees of several hundreds of pounds depending on the size of the property and the extent of the analyses. Common sense should tell anyone that you won't get this type of in-depth specialist investigation carried out within the range of normal 'free/low cost damp and timber surveys! After all, you wouldn't expect to get a £10,000 car for a £1000!

Fair expectations:

What a client should expect, however, is a reasonable interpretation of data from standard non-destructive surveys. This should give over 95% correct diagnoses.

A few rare cases of the 'old rising damp, salts alone' scenario will occur, and when confirmed by proper destructive testing could the client regard the original non-destructive investigation as negligent? In my opinion - and this is only an opinion, no - provided the surveyor has made a reasonable interpretation of data from the non-destructive evaluation, and reported the limitation of such investigations clearly.

Thus, it is essential to advise the client in the report that the findings have been interpreted from the use of non-destructive techniques and as such, by necessity, there are limitation. Perhaps a sentence in the report based around something like the following might help:

"The above findings are based on the interpretation of results from a standard non-destructive inspection; this, by necessity, has limitations. If you require confirmatory/definitive diagnosis of our findings then this can be undertaken by the use of destructive methods of investigation: these will involve some damage and costs."

This explains to the client the limitations of the current inspection, but gives them the opportunity for more detailed destructive analysis of the problem - but at a cost.

Finally, consider that if the above problem of 'salts only' occurs then at least there will be a good argument for replastering even if there is not the scope to insert a damp-proof course. After all, the replastering is far more expensive than the damp-proof course!


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