Rubble Filled Wall...repointing??

[jungle_jim01]

Hi, I'm currently in the process of raking out/repointing my Sandstone House. (thanks to everyone's advice last time i posted...getting to grips with the lime mortar!)

I've started on a lean-to extension which must have been built in the early 1900s i reckon. The lean-to is brick (which i'm not repointing)...but one end is formed by a much older Sandstone wall. It looks like this may have originally been a garden wall which they've used to form one end of the lean-to. From the outside this wall doesn't look too bad apart from bodged cement pointing ontop of the older lime stuff! As i'm pulling out the loose cement pointing, i'm finding some quite large voids and it appears to have a rubble infill. My question is...can i just pack in the lime mortar and build up slowly or should i be trying to pump some grout or something into the middle of the wall??

Thanks for any advice

 

[Anonymous]

For a grout to be introduced into the wall core you will need to ensure that both faces are pointed up with a hydraulic lime mortar so that there are no voids for the grout to escape. The grout should consist of 1 part NHL 3.5 hydraulic lime to 2 part builders' sand, mixed to a wet runny mixture. The grout will find it's way down to the foundations - if you notice any leakage whilst the grout is being poured in, the holes can be temporarily 'plugged' with clay or wet newspaper. Allow the grout to set before working your way up the wall. You should expect to use about 300 kg of dry mix for each square metre of a 600mm thick wall.

 

[Flyfisher]

Would it be helpful to add new rubble into any large voids or would a suitable grout be just as good on its own?

 

[chuckey]

What I would do is to fill ex-supermarket plastic bags with glassfibre and push them into the holes with the "open " end down. Keep on doing this until the void is full. My reasoning is that the rubble infill serves no purpose other then to increase the instability of the wall and to provide a lodging spot for detritus and vermin. Putting in the glass fibre will increase the insulation of the wall albeit only minutely unless you do the whole wall. The reason for the plastic bag is to stop the GF getting waterlogged, likewise putting the bag in upside down make sure it does not fill with water. You should end up with a tight plastic bag backing to your hole against which you can point.
Frank

 

[jungle_jim01]

interestingly...in one small void i pulled out a total of 35 snail shells! Shocked me a bit but how much of a problem is it to have life inside the wall?

 

[Andrew Bodenham]

jim,

Unless there are structural reasons to grout or otherwise fill in the void in your wall I'd leave it well alone. I remember being a bit disturbed by finding loose infill and voids when I first started work on my house, but I have a better understanding now. The infill acts in the same way as the cavity in a modern brick-cavity-block wall, i.e. it allows water which penetrates the outer skin of masonry to run down inside the wall without (hopefully) passing through to the inner skin. It also traps air in the voids which has an insulating effect. Filling in the void and creating a solid bridge between outer and inner skins can provide a path for damp ingress and heat loss.
As regards life, your walls will contain their own ecosystems - everything from tiny insects up to mice, possibly birds and bats too. If this bothers you then you'll take great care to point up all the bigger holes that the critters get in through. Otherwise, so long as the inner skin has good integrity you can just let them get on with it and coexist harmoniously.

 

[Anonymous]

When the wall was originally constructed the core would have been filled with lime mortar and dressings from the stones, otherwise known as 'heartings'. Over time the mortar erodes and the core will settle. The inner and outer 'leaves' of a solid stone wall are tied together with 'through stones'. If the core is left to progressively deteriorate then this can lead to structural problems such as bulging of the outer or inner face. If a hydraulic lime grout is used this effectively returns the wall structure to something similar to what it was when first constructed. If the wall is in an exposed location then the voids between the stones need to be fully packed with sound mortar otherwise there is an increased risk of wind-driven rain finding its way to the inner face.

 

[Penners]

Bolection clearly knows a whole lot more about this subject than I do. Nevertheless, I tend to agree with Andrew.

My limited experience of stone walls was gleaned in Oxfordshire. The traditional practice there seems to have been to build stone walls as two skins with a void between them, which was filled with loose rubble, known as "dross". No attempt was made to grout this infill.

So long as the two outer skins are sound and suitably load-bearing, there is no reason to worry about the looseness of the dross, or about its little menagerie.

If the outer skins have large holes in them, these can be filled with smaller pieces of stone, lime-mortared into place.

 

[stuart45]

A similar method was used in Somerset, my own cottage has 20 inch stone walls with a lime/rubble infill. If the rubble isn't stabalised with lime mortar it will settle in time and leave voids. The same thing happens behind a fireback causing it to crack. The reason for not adding lime mortar to the rubble infill was probably down to poor workmanship and saving materials.

 

[Anonymous]

The reason why a fireback cracks is that it hasn't been installed correctly. Before fitting a layer of cardboard should be taped across the rear face of the fireback before the rubble fill is put in. When the fire is lit the card will char away over time, thus leaving a small gap which accommodates expansion and contraction. This gap limits the likelihood of cracking.

Firebacks were traditionally manufactured in 2, 4 or sometimes 6 sections and would be assembled on site with fire cement at each joint. Therefore, as the clay expanded and contracted the movement would be accommodated at the joints - not across the face. As hairline cracks develop at these joints - which will inevitably happen - it is simply a matter of raking out the joint and repointing it...which is much simpler, and cheaper, than taking out the whole fireback and replacing it.

As manufacturing techniques evolved during the 20th Century firebacks began to be manufactured in complete whole units. If you buy one today from a Builders' Merchant you will usually find incised lines in the clay where the joint would originally have been. If you wish you can cut the fireback along this line with an angle grinder and assemble it in sections as would originally have been done, with a full bed of fire cement at each joint.

A word of caution for anyone who is thinking of taking out a fireplace or replacing a fireback - asbestos rope was traditionally inserted at the junction of firebacks and cast iron surrounds to seal the joint.

 

[worms]

The reason for not adding lime mortar to the rubble infill was probably down to poor workmanship and saving materials.

(Just to be argumentative ) Given that many of these walls have survived 100 years or more it could simply be because it would have been unneccessary and extravagant!

 

[Schoolmarm]

http://en.wikipedia.org/wiki/Angkor_Wat



This building was on telly last week. Utterly amazing and built with NO mortar whatsoever merely the tightly fitted together stones. Jaw still on floor.


The roof stones had been made with a special internal groove to send rain water away. The restorers and caretakers had blocked this off with cement fillets. Untold damage has been caused below.

 

[Flyfisher]

Amazing on two counts:

1. I didn't know it was built without mortar :shock:

2. The first time I've seen the word 'quincunx' used in a different context to digital video systems. There I was thinking it was a special techno-babble word but it seems it's long been used in architecture. Still, I suppose architecture predates video. :lol:

 

[Anonymous]

The reason for not adding lime mortar to the rubble infill was probably down to poor workmanship and saving materials.

(Just to be argumentative ) Given that many of these walls have survived 100 years or more it could simply be because it would have been unneccessary and extravagant!

It depends which part of the country you are in. Solid stone wall constructions vary significantly throughout the UK. If a solid stone wall had been constructed in the Yorkshire Dales, for example, without lime mortar being added to the heartings then it would have stood little chance of withstanding the exceptionally inclement weather.

 

[worms]

If a solid stone wall had been constructed in the Yorkshire Dales, for example, without lime mortar being added to the heartings then it would have stood little chance of withstanding the exceptionally inclement weather.

Hmmm... This place might suggest otherwise!

 

[Andrew Bodenham]

bolection wrote:
When the wall was originally constructed the core would have been filled with lime mortar and dressings from the stones, otherwise known as 'heartings'. Over time the mortar erodes and the core will settle. The inner and outer 'leaves' of a solid stone wall are tied together with 'through stones'. If the core is left to progressively deteriorate then this can lead to structural problems such as bulging of the outer or inner face. If a hydraulic lime grout is used this effectively returns the wall structure to something similar to what it was when first constructed. If the wall is in an exposed location then the voids between the stones need to be fully packed with sound mortar otherwise there is an increased risk of wind-driven rain finding its way to the inner face.

I think we have to be careful of generalisations here, as there are clearly variations in local building techniques. I can only report with certainty that in the coastal N.Lancs village where I live I have encountered several properties where the walls appear to have been constructed with loose rubble fill, with no evidence of any mortar having been used in the heart of the wall. They seem to be to be surviving the brisk weather we get here pretty well.

 

[Anonymous]

bolection wrote:
When the wall was originally constructed the core would have been filled with lime mortar and dressings from the stones, otherwise known as 'heartings'. Over time the mortar erodes and the core will settle.

I think we have to be careful of generalisations here, as there are clearly variations in local building techniques....

As I said in my last post "...Solid stone wall constructions vary significantly throughout the UK...".

 

[ChrisD]

The advice I was given, by a structural engineer specialising in period properties, was to repoint with lime mortar
and to use cementatious grout for the infill. The idea was that the grout would bond the outer and inner skins (anchors were also mentioned) to prevent leans, bulges, etc caused by separation of the two skins. Is this wrong? From what I've read here the properties of lime mortar would not be effective for this purpose - I thought that this would be why the original builder paid little attention to mortar in the infill.

 

[Anonymous]

The advice I was given, by a structural engineer specialising in period properties, was to repoint with lime mortar
and to use cementatious grout for the infill. The idea was that the grout would bond the outer and inner skins (anchors were also mentioned) to prevent leans, bulges, etc caused by separation of the two skins. Is this wrong? From what I've read here the properties of lime mortar would not be effective for this purpose...

I rest my case. No, the advice you have been given Chris is quite correct. The term 'cementitious' is often used as a generic term - for Historic properties the grout is lime based. You can either buy it pre-bagged or mix it yourself as per my first post. A ready mixed bagged grout such as Tarmac's Limelite Heritage Grout 7 is often specified - "Heritage Grout 7 is used for void filling where medium strength and absence of Portland cement hydrates are desirable. Hydraulic lime is used as the key binder. The product has been designed for World Heritage site projects and in particular, church, cathedral and other ancient structures that require repair using traditional materials and techniques."

The anchors to which you refer would typically be helical stainless steel fixings which are retro-fitted through the wall and resin bonded to the inner and outer 'skins'. There are several products on the market - the most common is the CemTie manufactured by HELIFIX. These are specifically designed to stabilise rubble-filled walls.

 

[Schoolmarm]

The best way to hold two skins together is using through stones with really good contact points above and below.

That is how those blackhouses were built.

Relying on cement is not good, several walls have stones that just ping off. If bad enough the whole skin will peel off.


The term "key binder" is meaning I think, the stuff to bind the sand grains together, not to bind the wall together.