Failed rendering - recommended approach

[RogerS]

The rendering on the corner of our house has failed. I will get my plasterer in to do the work but I was wondering how soon before he comes I should hack off the old render.  

Or is this something that I should leave to the summer?  Thinking about water getting down inside behind the render.  I'm actually probably going to get him to redo the entire bottom part of the front of the wall as it all sounds loose.  Getting the new render to bond to the underlying grotty stone is going to be fun.

Underlying wall construction is friable stone on grotty lime mortar.

Thanks

 

[Mike B]

I have similar issues with our place and so will be interested to see what the response is.

As far as I can make out, it is actually better to do the rendering in the spring as the summer can be too hot as the mortar dries too quickly, and the winter too cold so it can freeze.

Getting it to bond with the underlying wall seems to be a bit of a black art, but if you have lime mortar in the wall then you probably should use a lime render, but this will likely depend upon what the rest of the render is. It should get progressively weaker and finer grained as you work your way out.

Your walls also appear to be painted - any idea what with?? If it is not a breathable paint then this may also cause the problem you have, as when water does get through a hairline crack etc it can't get out and then it freezes and then...

Cheers
Mike

 

[AndyT]

Rigid impermeable coatings don't work on soft permeable walls. Once there's the slightest flaw, water gets trapped behind the surface and can only escape through the wall into the house. A good thick layer of lime is the answer.

We have a Victorian house, stone and brick, facing south west, and the back wall had been cement rendered and painted. I now know that's the wrong treatment and we have had it all removed and replaced with proper lime mortar and limewash. Specialist builders are available if you look for them!

Trouble is, most builders don't have the skills and patience and will offer to replace with more cement render and paint.

Best time to apply lime is spring or autumn - frost free overcast weather is best.

 

[OLD]

Watched a program called reclamation on tv with a stone wall that had been pointed with cement it had blown and the stone delaminated . The recommendation was use lime putty to let it breath and remove the cement to minimise further damage.

 

[mr grimsdale]

A neighbour of mine has had a proper trad lime render applied by experts to her house. It's what I would have recommended myself (on the strength of all I've read about it). I'm glad I didn't as it is dropping off dreadfully after it's first winter.
We rendered a house some years ago with similar soft sandstone walls to yours. Nothing will stick to it for long so we fixed SS mesh with SS screws into long plastic plugs, and rendered to that. It's still there 20 years on, but the render + mesh will be effectively a separate skin, with the stone underneath still softening away. It'll be interesting to see how it fails, as it surely must sooner or later.
It could be better to expose poor sand stone and just point with soft lime mortar, replacing stone as necessary as it fails (if it does). Portland cement mortar seems to be utterly incompatible.

 

[RogerS]

Thanks for the replies so far.

The house is a typical farmhouse ...ie bodged over the years..and that included cement rendering and non-permeable paint. Then I added to the problem shortly after we moved in by applying liberal coatings of water repellent...well, I didn't know any better at the time.

It is hard to decide what to do. The resource isn't a problem as I have an excellent working relationship/friendship with a conservation plasterer. What John doesn't know about lime work, isn't worth knowing. The front could do with the whole lot taking off as over the years the front wall bowed both vertically and horizontally.

When we bought the place 20 years ago, our builder tied the front wall back to the middle wall but you can still see the tatty rendering over the metal crosses he used to spread the load. That plus numerous cracks (well, what do you expect with no foundations on a hill on clay) I did talk to John about redoing the lot.

His advice at the time was to not do it simply because we had no idea how the new stuff would adhere....Mr G's post is very apposite.

I'm planning to knock a hole in the side wall to put in a new sash window this year and so maybe I'll wait until then.

Still undecided whether or not to hack off a large section to see what it's like underneath. Just a bit concerned about water.

Leaving the front stone/mortar is not an option. LOML would string me up.

 

[matt]

Is it my imagination or has the whole bottom section of that wall been attended to in the past? There's appears to be a line from front to back of the house under the window.

 

[trousers]

Hi Roger
Not sure I envy your dilemma really.
Flexible substrate (stone/lime mortar) built on flexible foundations = potential for render to crack ever after.
Lime render if applied by someone who knows the material is probably your best hope, and overpainted with an appropriate product.
As Grim has said, there's a lot of merit in just letting the whole thing breathe without a render covering. The downside of this though is that a lot of this type of vernacular building were constructed of a bit of a ragbag mix of stone/brick/rubble, that was never intended to be "face work", and consequently don't look too special even with careful repointing (which can often end up more pointing than stonework in appearance).
Stone, like brick, to me should never be rendered (or worse painted). But until you strip your render, you won't know what you're up against with the substrate.
If it were me I would have it all off now and let the walls breathe cos the render may actually be trapping moisture behind it.

 

[Ironballs]

It does look that way, I thought the same thing Matt. I'd be inclined to let winter run its course and get all the freezing over and done with, then repair.

The frost this winter has been bad and not helped by heavy rain in the early parts which soaked everything through. Several of our years old plant pots have suffered this year and been delaminating like buggery

 

[RogerS]

Thanks guys. Well spotted, Matt. That crack has been there before we bought it. Kept filling it. Kept opening up. Silicon filled the gap.

 

[JFC]

Sorry to say it Rog but it looks like dry rot to me Typical conditions with a down pipe and timber covered over with a small skim .
Try exposing more of it and see if there are any root like feelers / spores .
I really hope i am wrong !

 

[RogerS]

Sorry to say it Rog but it looks like dry rot to me Typical conditions with a down pipe and timber covered over with a small skim .
Try exposing more of it and see if there are any root like feelers / spores .
I really hope i am wrong !

Fortunately I think you are !!! There is no timber this side of the building.

 

[RogerS]

I couldn't stand the suspense and so went out and hacked some of the render off to reveal .................brick! That surprised me as I really thought that the front was stone. That's the good news as in extremis it does give a very good anchor point if i go down the mesh route.

The bad news? Very badly spalled on the corner. I reckon that that render must have cracked pretty badly just before winter and that let in water which froze etc. Having said that there are some fine cracks on the front of the house which may also have contributed. Pretty sure the downpipe is clear and not overflowing.

Maybe mesh the bottom as that is where the bricks will always be damp from rising damp...the property was allegedly injected many years ago but whether (a) any guarantee is worth anything and (b) the company will still be in business remains to be seen. I may well get a quote for it to be redone...money out...money out.

Now here is the funny part. Did you know that if you re-render more than 25% of a wall then you are supposed to use insulating render to be compliant with Building Regs? That said render is supposed to be 80mm deep which would imply new cills, new door surround. :shock:

So somehow think a complete re-render is out of the question. Pity as the wall looks pretty duff when the sun is in the wrong direction.

 

[mr grimsdale]

It's the render that's wrecked for the brickwork. Retained damp, salts, frost etc.
Not much help sorry!

 

[matt]

Idle curiosity borne out of the mention of DP injection... Was the building constructed with a damp proof course?

 

[RogerS]

Idle curiosity borne out of the mention of DP injection... Was the building constructed with a damp proof course?

I doubt it very much, Matt. if so, it would have been slate most like. Plastic wasn't around then !

 

[matt]

Idle curiosity borne out of the mention of DP injection... Was the building constructed with a damp proof course?

I doubt it very much, Matt. if so, it would have been slate most like. Plastic wasn't around then !

You'll get this thread locked if you continue to state the obvious :lol:

 

[Lons]

Now here is the funny part. Did you know that if you re-render more than 25% of a wall then you are supposed to use insulating render to be compliant with Building Regs? That said render is supposed to be 80mm deep which would imply new cills, new door surround

I didn't know that. Must ask my BI mate on his next site visit to my extension. He might learn something as well. :lol:

Doubt very much that you can be forced to repair or replace any or all of your render with anything more than the existing finish.

Different sistuation if it were a new render project as that would alter the material and visual attributes of the property and could even require planning approval

 

[RogerS]

.....

Doubt very much that you can be forced to repair or replace any or all of your render with anything more than the existing finish.

....

It's there in black and white in the Regs...I checked !

So reality could be that if you had dodgy render you'd simply let it deteriorate further as it would be so damn expensive to do anyting else.

 

[Jake]

Idle curiosity borne out of the mention of DP injection... Was the building constructed with a damp proof course?

I doubt it very much, Matt. if so, it would have been slate most like. Plastic wasn't around then !

You'll get this thread locked if you continue to state the obvious :lol:

Touché!