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Sample Collection

There are a number of handy tips for successfully collecting mortar samples. They are as follow:

  1. Size Matters. The larger the sample, the more statistically reliable the results will be. Thus, it behooves the individual doing the collecting to obtain a large sample. The minimum size that is usually used is 20 grams, which, of course, means very little to those who are reading this. This translates into a chunk amounting to about the size of a walnut.
  2. Location matters. It is not good to mingle samples from various locations on the buildings because the mortar may vary significantly from area to area even though it may appear to be the same.
  3. Solidarity does not matter. Because the sample will be turned into its constituent parts it does not matter at all if the sample is a single, unified piece or mortar. This analysis does not test for hardness or strength.
  4. Bedding mortar and pointing mortar. Many masonry walls have both bedding and pointing mortar in them and it is important to separate the two because they are frequently different. Bedding mortar is the basic mortar used to lay the masonry units and pointing mortar is used on the exterior of the joints. Bedding mortar is typically a softer mortar with specific properties to ensure greater longevity of the wall. Lime mortar is able to move with the settlement of a wall over time, sealing cracks that develop. Pointing mortar, on the other hand, tends to contain a higher lime content. The reason for this is to resist weathering. While supple, pointing mortar is usually denser and harder than bedding mortar. Also, pointing mortar was frequently tinted in colors. For example, pointing mortar might be tinted with brick dust to create mortar matching the adjacent brick. Thus, it is very important that bedding mortar be analyzed separately from pointing mortar.
  5. Where to take samples. Some areas of the building are better than others for the collection of samples. If a sample of bedding mortar is desired, then collection from the interior, exposed face of a wall is better than an exterior face where one may not only encounter pointing mortar, but where weathering may play significant factor. In addition, collecting from the interior face is much easier because access is usually very direct and the joints tend to be wider, especially in rubble masonry.
  6. Collecting soft mortar samples. If the mortar is relatively soft and/or crumbly a sample should be relatively easy to collect without damaging the adjacent masonry units. If it is bedding mortar one can use a small chisel or a screwdriver and hammer. By gently tapping into the mortar and prying out the mortar from the joint one can usually accumulate a reasonable sample. If one is collecting pointing mortar care must be taken to remove only the pointing mortar and not any bedding mortar, which might remain attached to it.
  7. Collecting hard mortar samples. If the mortar is hard and dense then much greater care must be taken when collecting a sample. All too often the mortar is considerably harder and denser than the masonry units so that adjacent masonry is damaged when the sample is collected. In situations such as this it is best to collect the samples from an interior location if at all possible or, at worst, from an obscure location on the exterior.
  8. Bagging the samples. It is a wonderfully easy matter to pop a mortar sample from a wall, only to have it fly across the air and land out of sight. In order to help prevent this problem it is recommended that two people collect the samples – one to pry the sample loose and the other to collect it in the bag. The bagger should hold the bag directly beneath the sample location so that the sample will fall directly into the bag. He must also be prepared to catch any errant samples that pop away from the wall. The person who pries the sample loose must be careful to avoid damaging the adjacent masonry units and to land the sample into the bag.

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