Re-pointing victorian house

[Sal99939]

Hi all,

Hope everyone is well.

I have a property which needs some re-pointing.

The south-side of the property has had its re-pointing done before but it has not been done well. This was before my ownership. It is now in a poor state, so I am organizing to have this done as the weather is getting better. At the front of the house, you can still see the ash in the mortar mix.

I have done some research and as it is a Victorian property it would be better to have natural hydraulic lime motor mix to re-point.

However, I am adding a couple of air bricks to the top of the property and opening closed off ones at the bottom to allow for air flow and breathability, so would a normal mortar mix suffice?

Only asking as I know it takes a while for the lime mortar to dry and as British weather is unreliable, I do not really want to pay for the re-pointing for it to be washed away.

I am beginning to call around a few people for quotes, is there anything that I should be asking to ensure they do a good job? Or anything I should know before taking on this project.

Any help is appreciated, thanks in advance.

 

[ree]

OP,
If you post pics of the walls it might help?
Stick with a 3:1 sand & NH lime mortar mix - its the go-to standard for pointing and rendering in thousands of jobs.
Air bricks wont make much difference to pointing.
What "openings" have been "closed off" - are you intending to ventilate cavity walls?

 

[Sal99939]

OP,
If you post pics of the walls it might help?
Stick with a 3:1 sand & NH lime mortar mix - its the go-to standard for pointing and rendering in thousands of jobs.
Air bricks wont make much difference to pointing.
What "openings" have been "closed off" - are you intending to ventilate cavity walls?

I'll get some pictures this weekend.

There is some air bricks low down and somebody has used some clear silcone sealant to block it off. Maybe if somebody has had the cavity wall insulation done.

The idea with the additional air bricks is to ventialte the cavity and allow it to breathe and dry out.

 

[ree]

OP,
No, do not "vent" the cavity - for a number of sound reasons you dont vent any wall cavities.
Your "air bricks low down" should be opened up - they should be located below the interior floor level - they should also be sleeved through the cavity.
If you post pics of the brickwork I can say whether you have blown in CWI or not.

 

[stuart45]

Only asking as I know it takes a while for the lime mortar to dry and as British weather is unreliable, I do not really want to pay for the re-pointing for it to be washed away.

NHL 3.5 goes off almost as quick as a 6/1/1 mix when you are repointing.

 

[Sal99939]

OP,
If you post pics of the walls it might help?
Stick with a 3:1 sand & NH lime mortar mix - its the go-to standard for pointing and rendering in thousands of jobs.
Air bricks wont make much difference to pointing.
What "openings" have been "closed off" - are you intending to ventilate cavity walls?

See attached pictures.

First 8 pictures are of the rear of the house, south facing. Last 2 pictures are the front. Wouldn't allow me attach more but the front is in better condition than the rear.

I have had a quote from a local reputable building company, I've not used them before but they have a good reputation from people that have are regulated and insured. Below is what they sent on the quote. I have two more companies to try, both specialize in re-pointing.

Quotation This quotation is for completing the below works: Scaffold to be erected to the front and rear of the property so the front façade can be re-pointed. 2 boarded lifts with the top boarded lift erected so pointing works can be carried out. Legs to be foamed and allow for pedestrian access to the front of the property. If the sky dish is in use it will need to be removed and installed elsewhere while works are being carried out, it will be re-instated to its original position once works have been carried out. This is NOT included in the price of this quote. Fully grind out the mortar to the front and rear of the property to allow for works to be undertaken. Re-point the front and rear of the property using a 3:1 sand and cement mortar mix complete with additives. Alime Cement would not be required on this property. All waste to be removed from site and fully cleaned. Quotation cost £2,880 including V.A.T​

 

[ree]

OP,
Thanks for the pics & info.
The price you have been quoted is a good price.
1. A previous DPC has been injected - not much use in a cavity wall unless no original DPC exists?
2. There seems to be a sand & cement plinth - usually its best to remove S&C plinths.
3. One 9" x 3" air brick can be seen (remove it, its too high) - you need, say, three 9" x 6" a/b's front and rear. All installed below FFL.
4. No blown-in CWI has been installed.
5. "grind out" to a 25mm depth.
6. The last pics show stock bricks on the front elevation - stock bricks have very thin beds & perps. Care req'd.
7. Do you have signs of damp damage anywhere on your inside wall surfaces?

 

[Sal99939]

OP,
Thanks for the pics & info.
The price you have been quoted is a good price.
1. A previous DPC has been injected - not much use in a cavity wall unless no original DPC exists?
2. There seems to be a sand & cement plinth - usually its best to remove S&C plinths.
3. One 9" x 3" air brick can be seen (remove it, its too high) - you need, say, three 9" x 6" a/b's front and rear. All installed below FFL.
4. No blown-in CWI has been installed.
5. "grind out" to a 25mm depth.
6. The last pics show stock bricks on the front elevation - stock bricks have very thin beds & perps. Care req'd.
7. Do you have signs of damp damage anywhere on your inside wall surfaces?

Responses below, apologies for my lack of knowledge on this, I'm not in the trade and have never had this type of work done before.

1. A previous DPC has been injected - not much use in a cavity wall unless no original DPC exists?
Yes no original DPC, the injected DPC was done way before we purchased it.

2. There seems to be a sand & cement plinth - usually its best to remove S&C plinths.
Do you mean the black bit to the bottom of the front of the property. From memory I don't think there was one to the rear.

3. One 9" x 3" air brick can be seen (remove it, its too high) - you need, say, three 9" x 6" a/b's front and rear. All installed below FFL.
Would a a couple high level (top of first floor) ones be a good idea in addition to these? The floor is concrete not an elevated wood floor does the affect the location.

4. No blown-in CWI has been installed.
There is, the guy who quoted pointed out the drill holes for this, I suspect this is why the air brick has been sealed.

5. "grind out" to a 25mm depth.
Ok - thank you.

6. The last pics show stock bricks on the front elevation - stock bricks have very thin beds & perps. Care req'd.
Thank you.

7. Do you have signs of damp damage anywhere on your inside wall surfaces?
Yes damp to internal walls, we had a survey done and they concluded the moisture was being absorbed by sub-floor, underneath the asphalt, through the holes in the pointing and making its way to the center of the house. The chimney was removed to below the roof line many years ago so it was definitely not that. Also the rear garden floor (all flagged) was at an elevation sloping towards the property so rain water would flow towards the house. I had a channel drain installed to cover the width of the property and flow into the existing drain.

 

[ree]

OP,
2. I can only glimpse a possible S&C plinth in the rear elevation pic #8? The front elevation is not shown.
3. As my previous, air bricks "ventilating the cavity"are a very bad idea.
4. If all your floors are solid then air bricks are not needed.
5. My bad - after your correcting me, I can now see the CWI holes.

7. Pics showing the interior walls damp damage will help?
I'm assuming that, over ground soil, you've got concrete floors with an asphalt DPM on top of the concrete - if the asphalt is failing then pics showing failed areas will also help.
Water entering a cavity, even at the base of the cavity, could soak the insulation material depending on what kind of CWI was blown in?

 

[mrrusty]

No, do not "vent" the cavity - for a number of sound reasons you dont vent any wall cavities.

@ree - I see you are showing as California - this is a UK site dedicated to UK situations. IMO this is 100% wrong advice for the UK with our damp climate. My house built in 1902 was built with ventilated cavities - several brick sized airbricks that don't go all the way through the wall The ventilated cavity was discussed with my BC Officer when we were internally insulating and considering interstitial condensation risk. The conclusion we agreed was that any IC risk caused by cooler wall fabric temperature as a result of internal insulation would be mitigated by the ventilated cavity. (and so it has proved)

The air movement within the cavity serves two purposes - 1) it allows any moisture in the inner brick skin caused by interstitial condensation to be evaporated,and 2) similarly any penetrating moisture through the outer skin will like wise be evaporated by the air movement within the cavity. IMHO in older properties, built with a cavity, it is essential the cavity is ventilated due to the porosity of the lime mortar. It is a very good reason not to use CWI in an older property!

 

[ree]

Poster #10,
Thank you for your post.
Why do you think Air Bricks in new build are sleeved thro the cavity?
Why, in new build, are a/b's only installed below FFL - unless they are sleeved thro to particular rooms but nowadays its mostly trickle vents?
Many new builds have rendered half or full elevations - high a/b's dont pierce the rendering or EWI.
The idea used to be, until modern research proved it wrong, that venting cavities was good practice. Its not; cold air can bridge cavities - the cavity itself is part of the wall insulation.
Cavity venting reduces the U-value of the inner skin. It also can create drafts where frames are installed.
Cavities are, with good practice, closed at the top to prevent thro drafting and smoke funneling.

IME, swirling cold air doesn't respect "older properties" or newer properties which is why cavity vents were made obsolete quite a few years ago.

 

[stuart45]

High and low level air bricks as cavity vents stopped being used years ago, because they caused cold spots on the inner skin, and increased the U value of the wall to more than a 9 inch solid wall.
Ventilation in the cavity is still required for timber framed houses, but a more even flow is done by weep vents at DPC level, and in the past under the frames and eaves as well.

 

[mrrusty]

Thank you for your post.
Why do you think Air Bricks in new build are sleeved thro the cavity?
Why, in new build, are a/b's only installed below FFL - unless they are sleeved thro to particular rooms but nowadays its mostly trickle vents?
Many new builds have rendered half or full elevations - high a/b's dont pierce the rendering or EWI.
The idea used to be, until modern research proved it wrong, that venting cavities was good practice. Its not; cold air can bridge cavities - the cavity itself is part of the wall insulation.
Cavity venting reduces the U-value of the inner skin. It also can create drafts where frames are installed.
Cavities are, with good practice, closed at the top to prevent thro drafting and smoke funneling.

You are mixing up two completely different things.
Airbricks sleeved right through are for void ventilation - like underfloor. The conversation is irrelevant to new builds - construction methods are different.

In Victorian/edwardian houses, the cavities were NOT part of the wall insulation. First they are small - typically 2". Second, they were designed in to help keep houses dry. Don't forget, they were put in when houses had coal fires in every room, causing huge updrafts which required a flow of air in to the house to replace the air going up the chimney. So much air had to come in, that it was irrelevant whether the walls were solid or cavity as far as room temperature was concerned. Old houses often had open airbricks right through in to rooms to provide this replenishment ventilation

If you seal up an old house that was designed to have a ventilated cavity, you are changing the way the house works. Our own 1902 now has considerable internal insulation, which works well to keep the house toasty. However, inevitably we have shifted the dew point within the walls inwards because the brick will now be colder. Interstitial condensation is absolutely inevitable because it is impossible to seal-up a 120 year old house in the same way we seek airtightness in new builds.

In effect, the structure of our 1902 is now very similar to a modern timber frame, with an insulated inner skin and a ventilated cavity before the external skin. As I say, I looked at this closely with building control at the time we were insulating, and we agreed the IC risk would be mitigated by the cavity ventilation. This is exactly what has happened - the insulation has worked well, and the ventilated walls remain totally dry.

Weep vents, drip points on ties, cavity trays etc, in more recent houses are there to mitigate water running down the inside of the outer skin caused by either penetration, or more likely condensation on the inside surface - the outer brick skin will often be way below the dew point of any water vapour migrating from internal - which is in incredibly difficult to prevent simply because just the temperature gradient causes a difference in vapour pressure, with the higher/warmer internal pressure tending to move water vapour to the lower pressure cooler areas.

In summary, airbricks and cavities in victorian/edwardian houses have absolutely zilch to do with any consideration of insulation and everything to do with controlling the dampness, condensation and penetration in the building's walls. It is only in more recent times that building design has evolved to make the cavity part of the insulation of the building.

https://historicengland.org.uk/imag...arly-cavity-walls/heag083-early-cavity-walls/ page 3

 

[ree]

Poster #13,
This forum is about technical advice, its irrelevant who gives it or where the poster might be located - the only issue is whether the advice is good or bad.
FWIW: I understand the issues in Remedial Building Work very well.

Page 3 of Historic England shares the truism that the cavity "allows for the evaporation of any condensation or rainwater" - it says nothing about air bricks high or low or venting the cavity? So what is your point in referring to Page 3?

No matter the age of the building, wall cavities, ie the air space, have, willy nilly, always been part of the insulation - I dont think you fully understand what you are posting?

Perhaps you've not noticed that the OP already has blown CWI and proposes to install high level air bricks to vent an already full cavity? Thats the only ref to your confused "zilch" conclusion.

My point about modern research concluding that venting cavities period was bad practice still stands - it was bad practice in the past and it still is.
Timber frame perp vents are different.

For zilch, most of your posts seem to be shouting in an empty room.

 

[mrrusty]

whatever - you have to get to page 5

In the early days of cavity construction there was
much debate about whether or not the cavity
should be ventilated. However, by the end of
the 19th century a prevailing consensus had
developed that there should be a small amount of
ventilation, similar to that provided under floors,
but that the cavity should be closed effectively at
openings and beneath the roof line. This provided
a degree of air movement to help any moisture
which did penetrate the cavity to evaporate away.

I take the point the OP has CWI, and if it's a victorian property IMHO he would be best to get it removed...

I repeat that at the end of the 19th C beginning of the 20th cavities were for damp control not insulation. I'll stick to my opinion backed up by my qualifications involving condensation control, and you can stick to yours. Everyone is entitled to their opinion.

FWIW my own house has 10 airbricks installed solely to ventilate the cavity and they work as well today as the day the house was built.

My advice to @Sal99939 is to use lime mortar if you can, open up the airbricks which certainly can't do any harm even though you have CWI and see how you go. If you get any damp crossing through the CWI, (as is not uncommon) think about getting it removed. https://www.heritage-house.org/damp...wall-insulation-1/cavity-wall-insulation.html