Insulating render...

[Persis]

Hi everyone

We have a 1890 house which has some mysterious damp patches on the walls. I had a damp surveyor out who said I needed to rip all the plaster off the inside walls, lose all my pretty coving and re-inject the damp proof course. However i got the Haynes Guide to Victorian houses based on a recommendation from this forum, read it avidly, then went around my house banging on the render with a plank and found that the damp patches pretty much correspond with areas of blown render. So I think I will try getting that sorted out first.

I've had a recommendation for a company from a friend with another old house. Hers needed the render replacing, and she is really happy with their work. They put on a layer of insulating render and it has made the house much warmer, and also dryer. Which sounds fantastic. HOWEVER I have 2 questions I would love some help with:

1. If I insulate the outside of the house (it would only be the front and back as the sides are brick), will this make my house less breathable and thus damper? I am a fan of open windows (well, they are currently painted shut but when they are fixed I will be), I run a dehumidifier constantly, and next on the hit list is lifting the floor to sort out the airbricks.

2. Is it ok to do this kind of work in the winter or should we wait until the summer? If so, is there a way of me just waterproofing the blown patches to tide us over until then without compromising the final job? I am NOT skilled in this area but I would really like to redecorate inside as it is a very dismal room at the moment, but there doesn't seem much point when it's just getting wet all the time.

Also a quick thanks to you all for saving me £10k and lots of lovely things in my house by all the advice!

 

[aockenden]

Hey, whether or not this insulating render will make your house less breathable is completely dependent on the composition of the current render that will be replaced and the new insulating render which will be added. Tell us what both are made of and we’ll tell you whether your house’s breathability will increase or decrease. To be clear, adding insulation to a house is not intrinsically linked to an increase or decrease in breathability, it’s entirely down to the materials and approaches used.

Any external render work is safest done when there’s no risk of frost for a period of time. That frost-free window of time also depends on the composition of the render. This is a great way to probe the contractor you are considering for the work. Ask them when they are planning to do the work and hopefully they’ll talk about frost risk so you know it’s at least on their mind. If they are proposing to do it in the dead of winter, then ask them very innocently “oh I thought I heard someone say frost might be a concern while rendering” and observe their reply.

 

[Persis]

I like the idea of dropping it into conversation! I did that with the damp person - my first clue was that even when I pointed out my half-blocked airbricks they didn't see a problem when I KNEW from this forum they are (also literal common sense as surely the point of an air brick is to let in air!!) I currently have no idea what the render is made of or what the new render will be but I will try to find out (it is painted but there is a bit where the paint has flaked away i could look at. It is not a house that has had a particularly sympathetic set of renovations done so I would probably imagine the worst....

 

[aockenden]

I like the idea of dropping it into conversation! I did that with the damp person - my first clue was that even when I pointed out my half-blocked airbricks they didn't see a problem when I KNEW from this forum they are (also literal common sense as surely the point of an air brick is to let in air!!) I currently have no idea what the render is made of or what the new render will be but I will try to find out (it is painted but there is a bit where the paint has flaked away i could look at. It is not a house that has had a particularly sympathetic set of renovations done so I would probably imagine the worst....

Ok then I suggest you learn deeply about the fabric of your building and learn deeply about the external insulating render system being proposed before committing to anything.

 

[Cubist]

Sorry Persis but that Damp Surveyor you engaged..... is a charlatan who is trying to rip you off. If I were you I would be burning any documentation he supplied as not worth the paper its written on and erasing his contact details from my various devices and formally complaining to ay trade body he may be associated with while considering making an attempted fraud charge to the police!

His proposals are, to my mind, utter rubbish and you need to get your Nikes on.

 

[Persis]

Don't worry @Cubist she is erased from my memory. And it was a free initial look around so I'm not out of pocket, just a bit annoyed!

@aockenden I would LOVE to know more about my poor, suffering house....but how do I find that out? Can I scrape a bit off and send it to be analysed or something? Is there a test? I like the look of this company because they are EVANGELICAL about careful repainting of victorian bricks (an issue we had in our previous house) so I can ask them if suppose....

 

[Cubist]

You're merely annoyed... I would be Furious and looking for blood.

Unless your internal walls are literally running with water or you can feel movement over large areas when you merely press the plaster with the flat of your hand there is absolutely no need to disturb it. All that may be needed are some patch repairs to small areas.

@aockenden and others here have a lot of relevant and good personal experience with external render systems and methods and are well worth listening to.

Cheers and Good Luck

 

[Persis]

Thank you - definitely not that bad and I taped a bit of foil over the damp patches (tip from this forum) and neither side felt damp so that was very pleasing. We have the radiators there turned up high so that's helping too. And a dehumidifier blasting at it.

 

[paulc]

A good chance the paint is a non-breathable type such as Sandtex. The fact it is peeling off would support that suggestion.
You could take a sample of the render, drop it into a pot of vinegar and see if it fizzes. Cement and resin based renders won't fizz, but a lime one should. However, you may get a little bit of fizzing if a cement render has a lot of lime in it, so not a conclusive test.

If you are going to the expense of putting up scaffolding, it is worth doing all those other little jobs at height at the same time. So gutters can get cleaned out, windows & fascia boards painted, and minor roof repairs done. Wait until spring, and you should have much better weather to do the work. Also filters out the charlatans - Decent tradesmen are booked up for months ahead.

 

[TudorCottage]

In my limited experience (enthusiastic DIYer non professional) lime mortar crumbles much more easily than cement when tackled with a hammer and bolster.

Sandtex now do a microporous masonry paint. I noticed it in (Swear Word Alert!!) B&Q when getting some electrical stuff. I’ve never used it but it was extremely cheap.

 

[aockenden]

@aockenden I would LOVE to know more about my poor, suffering house....but how do I find that out? Can I scrape a bit off and send it to be analysed or something? Is there a test? I like the look of this company because they are EVANGELICAL about careful repainting of victorian bricks (an issue we had in our previous house) so I can ask them if suppose....

There are lots of ways to gain insights into the existing building fabric. You can drill small holes and collect the debris that comes out of the hole, you can remove inconspicuous sections to explore the layers all the way back to the original substrate. You can use flexible endoscopes to look into hard to access areas. We can possibly make informed guesses based on pictures, etc.

 

[Persis]

Sounds exciting! It's a big week at work but I'll try to take some better photos and scrape a bit off to look at.

It does have lots of little jobs that need doing up high so it's a good plan to do them all at once in the spring. I need to save up as well I expect!

Thanks again everyone and hope it was a good weekend for you all!

 

[Persis]

@aockenden I've just read your sheep's fleece insulation project....looks so cozy and lovely!

 

[aockenden]

@aockenden I've just read your sheep's fleece insulation project....looks so cozy and lovely!

Haha thanks, yes we still don’t have a door installed on that building so it’s not actually heated yet but our little woodburner arrived last week so once the door is on and the woodburner is installed it WILL be cozy and lovely. That’s the same building where we’re doing our insulating clay + charcoal plaster / render internally (seen in another of my project threads).

 

[Persis]

I've seen that too - looks lovely!! Looks lovely in black too i think!