The following procedure outlines the method used to obtain samples from a brick or stone wall. The procedure to remove a sample from a solid floor is basically the same. The sampling method does require holes to be drilled into the wall or floor surface, so it is essential that drilling is restricted to locations that are free of electrical, plumbing, and others services to avoid personal injury and damage to these items. In addition, drilling disrupts wall decorations, plaster, and other surface coatings. If you are thinking about removing samples, it is likely that damp will have already caused some cosmetic damage, so this is probably not a concern, but you should not proceed if there is any possibility of electrical or plumbing services being hidden within the construction or otherwise damaged by removing samples. If you are in any doubt, please contact us before you start.
When sampling a wall, the best results are obtained by profiling. This requires the removal of a sample from the base of the wall (as close to the floor as possible), with additional samples obtained at incremental heights of 150mm until you are above the visible damp line.
On the other hand, if you simply want an idea of the moisture content of the wall, perhaps to find out if you might have a problem, we suggest removing a single sample directly above the skirting board because this causes the minimum of disruption. Better results are obtained with a full wall profile, but this single sample method is often surprisingly useful.
It is important to use a sharp masonry drill bit and to drill slowly to avoid drying out the sample. We recommend a 10mm diameter drill bit if possible, but thinner drill bits, down to 7mm in diameter, can be used. The most important thing is to make sure the bit is sharp and to drill slowly.
If the wall is plastered, and most are, the plaster part of the drilling should be kept separate from the drillings obtained from within the wall. This is because the plaster usually contains the highest amounts of contaminating salts.
Drill into the plaster, it is usually around 20mm thick but can be more or less than this, and collect the drillings as they fall out of the wall. A plastic cup or similar held beneath the drill hole is useful for this purpose. Once the drill bit passes through the plaster, and you will know this because the drill often feels like it has hit a harder material or the colour of the drillings change, stop drilling.
Place the plaster drillings in a polythene bag and seal it. Place this polythene bag in a second polythene bag and seal that as well. Alternatively, you can put the sample into a 35mm film canister or a similar container. Another option is to get in touch with us, and we will send you some suitable sample containers. Whatever method you use, it is essential that the bags or containers are airtight and sealed well enough to survive a trip through the post.
When you have sealed the plaster drillings in their bags or container, go back to the drill hole and continue drilling into the wall to a depth of about 50mm. Collect the drillings as they fall out of the hole and place these into polythene bags or an airtight container as described above.
Clearly label each sample with the property address, a unique reference number, the room or location, and the height above the floor from where it was removed (e.g. kitchen rear wall, 150 mm above floor). It is useful if we are provided with photographs as well.
These instructions should provide a good indication of what is needed to obtain the masonry samples. It is quite easy, most people already own the necessary equipment: an electric drill, masonry bits, and polythene bags, and it is well worth the effort to find out how damp the wall or floor actually is. But you might have questions, and the process, at least to start with, will be unfamiliar, so why not contact us to discuss your project. Either send us an email or phone us on 01757 630530 for a chat. This way, we can clarify any questions you might have, give you precise instructions on what you need to do, and ensure that there are no delays in processing your samples.
© Britannia Preservation 2011