Re-point or rendering?

[Deleted User]

I own a Victorian (1890ish) house which is suffering from some damp problems as a result of damage to the pointing. I have been getting quotes from builder to repoint it and getting completely opposite advice. I have solid walls not cavity, limestone pointing.


The first builder said that some of the brick is deteriorating and will continue to do so. He recommended using K-rend and said this would be better at keeping the moisture out than just re-pointing.


The second builder (who specialises in repointing), said that the brickwork is basically fine (bar the odd brick that needs replacing) and that rendering, particularly on an old house like this, is more likely to seal moisture in than seal it out and will cause more problems than it solves.


Both are clearly trying to sell me the service they specialise in and I don't know who to trust. Aesthetically I would prefer to keep the bare brickwork but my main priority is to keep the damp out as I've had a dry rot problem in the past. Any advice? Thanks in advance.

Doozergirl

The second guy is right.

Rendering isn't a great idea for old houses and whilst the K-rend is flexible, it certainly isn't breathable and it can trap the moisture in.

If you re-point the house in lime, it will last as long as you do and it is exactly what was always intended for the house - the line will draw the moisture OUT.

If the house was working properly, moisture actually wants to escape from the house, not enter it. If you wrap an old house in a plastic bag, the moisture won't be escaping.

As for your damp and dry rot problems, there will be causes for those that need to be addressed. The cause will never be that 'the house isn't rendered'. You need to find exactly where the issues are and stop them penetrating the house. Not block the damp from showing with plastic and cement. One of the problems may well be the pointing, but there are many other places to look and most issues are solvable without too much expense.

[Deleted User]

Thanks for your quick reply! Re: the causes of the damp, there have been multiple over the years - I have had to have the roof felting replaced and guttering fixed. The remaining damp appears only in places where the rendering is visibly missing or cracked on the outside and so I feel quite confident that this is the cause.


Re: the re-pointing, I spoke to the first builder about doing this (because the second guy is unfortunately not available until after Christmas) and he said that it wasn't necessarily a case of cement versus lime but rather mixing lime into the cement. Does this sound right to you?

FreeBear

[Deleted User] wrote:

Re: the re-pointing, I spoke to the first builder about doing this (because the second guy is unfortunately not available until after Christmas) and he said that it wasn't necessarily a case of cement versus lime but rather mixing lime into the cement. Does this sound right to you?

You need to find yourself a builder that knows about period properties and when it is appropriate to use cement - The first builder does not fall in to this category.

Lime in a cement mix is purely added as a plasticiser to make it easier to get a smooth finish (e.g. for render). As a breathable mortar, the cement will clog up the pores and give you a hard, brittle, and water resistant filler. Kick anyone out who suggests cement.

A mix of NHL3.5 lime and sand is relatively inexpensive, simple to mix, and dead easy to use. Whilst it may take a few days to harden compared to a few hours for a cement mix, it will last a lot longer. However, it is starting to get cold out there, and you don't want to be repointing when there is a risk of frost - This applies equally to cement or lime mortars.

Get a booking in with your second builder for early spring - If he uses a pure lime mortar and no cement, he is just the guy you need. And while he is around, he should be able to repair any damaged sections of render.

stuart45

Although I've often used NHL3.5 for external pointing, I know a few builders who have started using hotlime, which is what was normally used in the past.
I have read a few reports which claim that NHL3.5 is closer to OPC than was originally thought to be.

FreeBear

NHL2 would probably be better, but few stock it. NHL3.5 is much more common. Use NHL3.5 for exposed areas and chimney stacks. For sheltered areas, a mortar mixed from lime putty would also work, but it takes a lot longer to harden - However, it does have the advantage that if kept in a sealed bucket, it remains usable for years.

stuart45

The problem with mortar mixes is that it can take many years for people to realize they were incorrect.
Back in the mid 60's we were taught at Tech to use a 3/1 or even 2/1 sand/OPC mix for repointing.
The theory back then was that a stronger mix would last longer.
Years later a 1/2/9 OPC/lime/sand mix started to be used for older properties, until the Smeaton project informed people that even a small amount of OPC could damage the mix.
I have used a 1/2/9 mix years ago on quite a few jobs, and not really been aware of any problems, although I can't say that I've been back and checked them all.

Apodemus

Lots of good advice above. Don’t get rushed into getting bad work done - the house is unlikely to suffer that much from a delay and it is much better to wait for the job to be done properly tomorrow than botched today.

[Deleted User]

Thanks for all your replies, they're really helpful. I'm going to wait and get it properly repointed with lime. I appreciate that this is the better option in the long run - it's just challenging because (a) my flat has had dry rot twice now, which has been super expensive to fix and the guarantee on that work depends on keeping the place water tight, and (b) partly as a result of that and financial precarity, I have fairly extreme levels anxiety about damp and I don't want to spend the winter having my mental health run into the ground every time it rains.