This week we hear from our Stonemason Foreman Paul, who recently worked for REDEC’s busy Refurbishment department on Walmer Castle near Deal in Kent…

During the works a number of leaks were found, these were traced back to two different windows. It was found that a combination of issues had caused the leaks; a box gutter that was getting overwhelmed during heavy rain and historic stone repairs that had been undertaken by the former keeper of the castle, the Ministry of Works.

As you can see in the photo a number of stones had been repointed in a cementitious mortar. This form of mortar would have been relatively new to the market during the early to mid-20th Century and the dangers of using such mortar was not known at the time. The mortar dries far harder than lime mortar (which should be used), it prevents nature moisture from leaving the stones, which leads to frost damage and cracking and its removal can also damage the in situ stones.
The other main issue with the cementitious mortar at Walmer is that it is not decoratively consistent. The original pointing was ‘galleted’, which calls for locally collected flints to be ‘knapped’ (cut into shards) and placed decoratively into the mortar beds. The ‘gallets’ are then stacked and cut to match the size of each respective stone in a decorative fashion. Part of our project here was to remove the faulty cementitious mortar, replace with a lime mortar (colour matched using ash and clay) and then ‘gallet’ throughout to match the mason’s patterns dating back to when the castle was originally built in the Tudor era.

The first task in repointing stonework is to accurately (to as far as reasonably possible) test what the makeup of the in situ mortar actually is. Sandberg LLP was appointed to test the mortar; they found that the mix used originally was a 1:1 mix of non-hydraulic lime and local sand. A similar mix was used, along with some fired ash and a hint of clay to colour the mortar to match the patina of the in situ mortar. Our stone masons used sand procured from a local supplier in Dover and added small quantities of the original mix back into the new mixes.

We then carefully removed the modern cementitious mortar, which luckily had not damaged the stones too much. Once the mortar had been mixed and the colour/finish approved by English Heritage and the Architect, the next task was to ‘knap’ the locally sourced flints to replicate the Tudor gallets. Knapping can take a considerable amount of time and can be very dangerous; fortunately our stonemasons are highly skilled for such tasks.
The finish as you can see below shows how well we matched the existing stonework and helped conserve this important scheduled ancient monument.

Paul our excellent stonemason had been with REDEC for over 9 years and first undertook his apprenticeship working on Westminster Cathedral some 30 years ago.