Chimneys repointed in natural hydraulic lime - Oxfordshire and Gloucestershire.
The chimney is the most vulnerable part of the house. Not least because it the part of the property which is most exposed, but also because of the effects of the changes in temperature which are brought about by solid fuel fires and wood burners. Their repeated use in winter means that brick and stonework is caused to heat up and then rapidly cool down once the fire goes out. Over many years, the resulting hot/cold temperature changes - in tandem with weathering - cause the brick, stonework and mortar to fail.
If you have an older property which was originally built with lime then it is essential to have the repair-work carried out using natural hydraulic lime and not cement. The reason for this is that cement responds to thermal changes at a different rate to traditional bricks or natural stone. The result is that rigid cement mortar will be pulled away from what it is holding together and eventually fall out in lumps and strips leaving the original lime to suffer further weathering.
If you click on the link below, I'll show you personally.
As cement is not porous it is unable to draw moisture from the surface of the bricks or stone. The impact of many winters of freezing temperatures eventually results in the surface of the masonry being ruined.
In direct contrast, lime will wick away surface moisture. Because it moves thermally at the same rate as your chimney, it will not crack and will last for decades.
When it comes to replacement, it is essential that the correct type of lime is used. Although NHL 3.5 is normally perfect for repointing older properties. It is not suitable for chimneys because of it is too soft. It's what's called a moderately hydraulic lime and is mostly used for general building and plastering. What's required is an eminently hydraulic lime. This is commonly known as a NHL 5 and is much stronger.
It will stand up to the elements in exactly the same was as a cement but is still porous and flexible enough to perform the function of allowing moisture in the building of evaporate whilst remaining flexible when the structure moves due to seasonal changes in ground conditions. It will also look many times better than cement, will last longer and overall will be kinder to your masonry.
Some close-up shots.
From the above photo you can see that NHL 5 is almost grey like cement. However, when you look at the photograph below you can see that things look very different when exposed to a bit of sunlight.
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