BLOWN RENDER - ANY ADVICE APPRECIATE

[Jacky123]

Hello

I have attached some photos of the rear of my cottage. It's 17th century timber frame. Unfortunately it has been repair with cement rendered (previous owner(s).

I recently had the exterior painted and the decorator brought this area to my attention. It's not the complete wall but an area of approx. 1.5 meter square. I don't know if you can expand my photos to see the problem. The photos are not great because the wall is at the rear of the property and close to the boundary wall. Anyway, I was advised to consider having all the render from this elevation removed, boarding applied, followed by Lime render. I have one quote so far which is:

Install scaffold, remove cement render, fix 25mm wood fibre backing board, lime render over wood fibre board. Apply breathable paint. Cost including skip but not including VAT is £ 7000.00 so £ 8400.00. Also this does not include replacing anything that may be damaged underneath. It's a lot of money, any comments or advice would be greatly appreciated. Thank you in advance.

 

[Lacan07]

what damage are we looking at exactly, to me it just looks like a badly rendered wall? Are there any signs of damp internally?

 

[larry]

Sorry, £8k to re render... What sort of sq m?

I had the front of my house done for under £4k, approx 60sq m, with NHL based render. Plus scaffolding costs of approx £800. So maybe £5k total. That didn't include decorating.

Do you know why this was re rendered in the first place (what was the problem they were trying to fix when they cement rendered) and most importantly as above what problems is it causing.

Is the render cracked? How do you know it is blown? And why can't they just replace the small section of cement render with NHL based if the other render is functioning OK?

 

[Jacky123]

It’s the area that has a pinkish tinge to it when you expand the photo, it’s about a meter and a half square. There are no signs of damp internally. The render is not cracked. When you tap it, it does sound hollow, apparently this means it has ‘blown’. I’m a complete novice and just repeating what I’ve been told.

 

[DaveG]

This does sound typical of a genuine issue. Cement render and hollow sounding.
It does sound steep to me but I’ve never had to get something like this done personally and I know lime rendering is a lot more costly than normal. Even the cost of materials I should imagine is a chunk of that but worth getting a couple quotes. You’re right to address it as left unchecked I’ve seen cases of entire sections of timber frame rotting and having to be replaced which can be major headaches.
Is this something an insurance company could help to cover if there’s a risk to the building structure?

 

[Cubist]

As a callow youth I learned that some 'dumb' questions occasionally produced some 'not so dumb' answers. Looking at some of the photos I'm seeing what I think are the the outlines of horizontal beams that would closely match those that would be beneath and immediately above the window frame in the pictures. Here's my 'dumb' question; any chance someone has moved that window frame to a new location, or installed a new one, and simply covered over the old opening in the wall before it was rendered?

If so you may find that the hollow sound you're hearing has a very simple answer. Alternatively you may also find that the original infill panels had significantly degraded before the render was applied.

Nevertheless, and as DaveG points out, cement render can be bad news for a timber frame house and judicial examination of the frames condition at low levels and at the junction of timber joints would be wise.

 

[Jacky123]

Thank you so much for your thoughts and comments, these have made me feel truly supported which is a great comfort. Cubist my home was a former cattle barn, so your theory could well be correct. I have attached a photo of the room behind the wall, it is the frame work on to the left of the window which is behind the wall. This may or may not support your theory, as a novice I have no idea what to look out for.

 

[Cubist]

Hi Jacky and thank you for this latest photo. It has, quite literally, thrown a lot of light on the problem but, again quite literally, from a very different perspective. This internal view of the frame and infill panelling, together with the information that the structure was originally a cattle barn, is very useful. My eyes were obviously deceived before as its clear from this latest view that there has never been a window where I had first thought.

It apparent also that the original infill panels were likely constructed of wattle and daub. Originally these walls would probably have been, at best, around 4 inches / 100mm thick and as they decayed or were damaged by weather of animals would have been repaired with materials already to hand from both inside and outside the barn. It's always quite surprising to me, and many others I suspect, how well those materials have lasted in such structures. But before I go wandering off into a dissertation on such, back to your immediate problem.

Just after we took on the stewardship of this old place I replaced the. back door which opened onto what is now our study/library. While finishing the installation of a new door frame I was hammering in some cotton caulking around its edge and the timber frame of the house when I was showered by a fall of cement render from an infill panel directly above my head. The complete panel of render had become dislodged due in part to my activities and also the decay of the mesh base into which the render had been pressed to form the skin of the panel that had fallen on to me.

I presently suspect that your external render may have been applied using a similar method as that to my own property. Could you conduct some small investigations/experiments please and provide some additional feedback?

1. Inside the house and in the area which corresponds to the hollow sound noted outdoors could you tap the wall and note the nature of the sound made? Also, using the palm of your hand could you firmly press against the surface of the panel to see if there is any movement or perhaps sounds?
2. Repeat these same steps outdoors and note any movement of the skin of the render and any small cracking sounds. Also, if there is any marked difference between sounds made when tapping the external render

I suspect that the external render has been applied by an unskilled person over a mesh of some kind, perhaps chicken wire, and that either the fixings of the mesh has parted from the frame or, more likely the inner surface of the render has broken away from the original infill material.

Please be aware, this is not the end of the world and the problem is probably not as serious as it may sound - in fact it may turn out to be a blessing in disguise.

Cheers for now,
Cubist

PS Theres another contributor here, Kearns, who has some considerable knowledge of timber frame buildings and he too may have some thoughts.

 

[Jacky123]

Hello Cubist

Thank you so much for taking the time to reply and in such depth; truly appreciated. I am sleeping better already.

I will do as you suggest this evening and report back, hopefully tomorrow.

Bye for now

Jacky

 

[Cubist]

Hi Jacky, I think I've just had one of those 'Penny Drop' moments. By any chance are the 'hollow sounds' reported by your painter most obvious around or near what would be the corner of the room indoors?

 

[Kearn]

I’m unsure which small area is the focus here, the external shots look like Stevie Wonder considered a career change. Or someone was aiming for that common 80s swirl pattern for ceilings? It’s more than just a patch repair though, it looks like the entire wall was approached the same way, or many many cover ups.

Theres no good reason for that haphazard finish, I guess they went on thick and fast and didn’t work the surface, possibly to cover the timbers / mesh / god know what else is under there with a thick coat.

How deep is the wall now? As Cubist says, you would’ve started with only about 100mm originally if timber, simply infilled, rather than covered. That will give you a guess of how much has been added externally. Alternatively, remove a section and see what your dealing with.

If it’s blown line render, it will still hold together and flex, just no longer be bonded to the substrate. If it’s cement, it’ll be rigid and hard and sound hollow. And likely show some cracks.

I can’t really see a specific problem area, the wall looks fairly consistent in its poor finish. If you know it’s cement, it’s not great, but not necessarily catastrophic either.

You say it’s repaired in cement - do you know when and why?

You can get away with cement render not doing damage. Don’t be swayed by no cracks to let water in and trap it though. Moisture will come up from the ground also and stay within the non breathable sandwich. But then I’d expect evidence of damp internally. What is your internal plaster and paint finish?

The lower black section would be red flag, often concealing a stronger cement mix as a plinth, which isn’t great at ground level and your sole plate probably won’t be happy on it’s lower and external faces.

What’s above? Thatch? Condition of rainwater goods? It looks like lots of darker damp areas on the wall and staining from wetness running down.

Gravel surrounding may be evidence of someone trying a French drain. Or you have a thatch? How is this ground level vs indoors? Looks like internally is engineered wood, what’s the sub base?

Back to your quote, it’s daft for 1.5sqm. That would be the entire wall. Very ballpark budgets are £150-200 sqm, but there are so many factors involved each job gets priced for what it is and requires.

I would guess that this whole wall does need addressing though, not just a small area as it all looks similar from photos.

His approach isn’t really standard - you can use wood fibre boards externally, but usually they would go within the frame depth, or over the frame internally to provide insulation benefit. Covering over an external timber frame isn’t normal, unless just a render / lime wash. Breathable external paints are rarely that, lime wash costs peanuts. Many of the breathable marketed paints contain chemicals / binders etc that limited their function.

I would expect the first part of this job to be investigation - open up some areas and see what you are dealing with and what the condition of underlying timber is. It’s impossible to quote without knowing what is going on, because you can’t know what the remedy is!

The most likely scenarios to follow would be best case, replace lime render either between timber infill or over the frame itself, but a limited thickness - too much isn’t a good thing as the thermal mass will be too thick and won’t function. Bad scenario would be timber frame repairs to sole plate and timbers that have been encased in cement rotting away. That also requires making good the damage to surrounding panel infills and paint etc.

It may seem counterintuitive. But a thinner wall with breathable materials will be warmer and healthier than a thick non breathable wall. Dry materials are good insulators, wet ones and good conductors.

 

[Kearn]

Also - if I follow your images, the hollow sounding section is to the left of your window looking from inside? Where the boxed in vertical protrusion is under your spine beam? Or is that a brick/block built support for the spine now that the two posts are no longer under it.

I’d really want to understand what that arrangement is all about - originally your spine beam would have jointed into your wall frame

 

[Jacky123]

Hello and thank you all for your valued replies. I am home now (was away last week) and yes Kearn the poorly outside render is to the left of the column. Yes the support of block/ concrete and there is one opposite on the other side of the room. Cubist the hollow sound is not towards the corner of
The house but close to the vertical column which Kearn references. If more photos would help I can do this now that I am home. Also the stains on the wall and not damp or water marks … my great neice got very creative and splashed dirty water colour paint up the wall.

 

[Cubist]

My 'penny drop' moment came when I saw that electrical supply sockets had been installed in the corner of the room and that wall lights had also been fitted. In these old timber frame houses electricians would typically route the supply cables beneath the flooring on the first floor and drill vertical holes in the uppermost exposed beam in the room below to then route the supply cables down to the required locations. Channels to contain the cables would be cut into the plaster and later buried. My thinking at the time was that, if the panels were constructed of wattle and daub, much of this would have failed during that process leaving voids that may well produce a hollow sound. Also, the outlet sockets would typically be mounted to a solid wood board buried in the plaster at installation. Temporarily removing the cover plates may give you some additional information about the panels construction.

That aside, it could be that the blockwork used to construct the piers, now supporting the large beam running across the room, could not be joined to the infill panels with anything other than plaster. It's likely then that the hollow sound heard comes from a cavity at the core and external wall side of the piers.

Going back to your original enquiry though. I would be cautious about how best to remove the external render if you choose to pursue that avenue. It may be an idea to try to carefully remove a small section to explore and understand just how the render was installed.

In any event autumn is coming and it will soon be time to put exterior jobs on the back-burner until next year?

 

[frustin]

Hi, when i looked at the original poster's photos they look like one of my walls on my new (300yrs) house. I was wondering, is yours listed? Mine is Grade 2, does that mean i'd have to get listed building permission to have a job like this undertaken?

 

[Jacky123]

Mine is not listed. I believe you may have to get permission, but I am not absolutely sure. I wonder if yours is listed, maybe you could get a grant towards the cost; just a thought .

 

[Jacky123]

The mystery deepens. As said previously the walls and beams inside were not wet or damp however, the small dehumidifier I have was taking about a litre out of this room each week. Today the flooring company arrived to remove the old linoleum floorings and this is what we found. I expect the water came in through the old window which did leak, this is the small one to the right of the pillar.

 

[Cubist]

Lino over a presumably concrete floor will prevent moisture rising from the ground below from evaporating into the atmosphere. Water will pool on the surface of the concrete and below the lino and will ultimately spread to any skirting boards and plaster with which it comes into contact. Also, the spread pattern of the staining seems to be centred on that column beside the window and not directly below the window itself and there do not appear to be any recent water stains on the sill beam. However, in timber frame houses penetrating rainwater can migrate in rather counter-intuitive routes.

I would strongly recommend that you get rid of all the lino as a priority - it can only harm your home by inhibiting its capacity to breathe effectively.

I would also suggest that you investigate those two columns to understand exactly how they are constructed and with what materials. I have a suspicion that the original timber posts that support the beam above that room are still there and have been boxed in somehow. Those posts need to breathe and boxed in like that they will rot and fail.

 

[Kearn]

Mine is not listed. I believe you may have to get permission, but I am not absolutely sure. I wonder if yours is listed, maybe you could get a grant towards the cost; just a thought .

Not a chance of funding sadly…

@frustin you will need LBC in order to do any major works such as removal / replacement of render, especially modern to lime as it’s a change of materials. Even if the right change back to what was originally there before someone else messed it up.

Some COs may say you don’t need to apply and can undertake as a repair, but doubtful. And finding your CO to have a conversation is often near impossible. A pre-app overcomes that. For a fee…

 

[malcolm]

If it is cement render (or a render painted with modern waterproof paint) over a timber frame building I would worry. Kearn's reply is worth another read. I had to replace a whole timber frame gable because it had been rendered in cement 100 years ago and the wood had turned into beetle dust. This time it might be a leaky window and next time maybe a crack, but there is a good chance water will be getting in that can't get out and the timber frame gets eaten away.

Good call to smash off a little bit of loose render yourself to see what is underneath. If it's all good then easy repair, but if everything is soaking wet behind it would make sense to smash off all the cement and lime render and lime wash. Woodwool boards probably aren't a good idea - they will make the walls too straight and reduce the chances for the wall to dry.

Wouldn't worry too much about listed building consent if you are removing cement and replacing it with lime. It's a repair and what are they going to do? I doubt the CO would ask you to put the cement back.