Renderers/ists builders -

Those are not settlement cracks, which would be diagonal. Nor are they cracks caused by thermal expansion and contraction of the building, as they would be concentrated at stress points like the corners of the windows. They look more as if the render has been well bonded to the substrate, but has shrunk, so the cracks have that 'map' pattern. Alternatively (hard to tell from photos) it may have expanded, causing local crushing, and then shrunk back. The pattern is reminiscent of the map cracking in concrete made with high alumina cement and reactive aggregate, which expanded (it shouldn't be that as HAC is banned for most uses now, but that's why I'm suggesting expansion as a possibility). Overall, it suggests a problem with the render mix, not the application of it.

Could this be freeze, thaw cracking?
Or has it been showing for months but the internal damp is recent.
Wondering if its trapped moisture or render that dried too quick in the heat wave. The water content is required to cure the mix, if it evaps too quick it could cause issues.

Thanks both

Good to read that its not caused by the house itself.

We noticed them during the warm spell in Sep/Oct. We went away on holiday & when we came back it had been raining and you could see the cracks as per photo #1. So not freeze/thaw (but thats obviously happened since & made them worse).
When we mentioned it to the main contractor he mentioned that it could be due to the sun being on the front for long hours over the summer. The render cracks are worse on the front but the skirt & window borders are cracked on every side.

Whats the solution? & expected outcome?

is it reasonable / likely to ask him to hack it all off & do it again?!

Is it reasonable / likely to ask him to hack it all off & do it again?!

That would be my plan, it looks like hydration cracking. If that's the case then it's either the wrong product used or application problems, but get an expert to give a proper opinion if necessary

Morning,
Speaking from experience. Owned and run my own building company fir 30 + years.
We have had an issue similar to this on a clients house. We had cracking that developed after a hot dry spell.
Are taking the time to find out what the issue was we put it down to differential movement. You have to check that the background your rendering onto will be compatible with the product, it needs to expand and contract at the same rate. If your house is poorly insulted you can get movement both in the winter and summer.
To resolve the issue we removed all render and added an anti- fracture slip sheet that we bonded to the wall prior to re-rendering. We now add this to all brick block render situations. We did this at our cost but if the product was specified by an architect or engineer and application process was followed you may struggle to get your renderer to re apply FOC.
Hope this helps. Happy to answer more questions if needed.

I'm no rough caster but can do it due to having a trade that uses cement, it looks to me like it may just be a one coat on top of the existing harl rather than the proper two coat ie scratch coat underneath and has no bond/strength then allowing water to soak through. Waterproofing / retarder is always used when dry harl like yours. It's used in probably 90% of Scotland buildings and I've never noticed it like that unless there was a damaged flue someone was trying to conceal ie paper over the cracks

Is it k rend or tyrolean coating.
My flat has the bonding / movement sheet and k rend. Still cracked but its tge ground shaking like an earthquake every 20 mins when the busses hit all the sunk drains in the road.
I would ask for a meeting with the builder and contractor, the builder recommends the contractor whose ultimate responsibility it is. But its not a great job. You could mention the danger if it pops on a hot day, moisture behind and differential expansion.
I use a 1'5 render mix, 3 parts sharp 2 parts soft for the scratch coat, then 2 parts sharp 3 soft for the top. Not a pro builder but acceptable for an amateur diy novice.

Get a skip in, you sds off all the damage render back to brick. Re point as necessary. Then get the builder back in with a bonding mesh and top coat.
Scaffolding required obvs, and k rend is not cheap anymore.

Does it absolutely have to be covered? In a reverse bit of logic your house will most likely be drier with faced bricks, or bricks painted with breathable paint.

Hiya,

Just a quick note. Your house has a cavity wall by the looks of it.
One picture shows the damp coming into the house by the window. The render is butting straight up to the frame. Plastic and render have differing expansion coefficients, the water obviously comes in on the gap between the two. We had water coming in similar on our single walled 200 odd year old house, between the stone and wall for similar reasons. I figured it out pretty early on, when we moved in. I just used a multitool with cutting dish to make a gap around all the windows and resealed them. You'll probably need to do the same. Here a lot of houses have been rendered over the stone and I noted all are cracked. Most people are removing the render these days and insulating inside to keep the insulation factor.
Myself I've just re-pointed all the stonework myself which has taken ages ;-(

JeZ

Read what @edthecarpenter has written, if I understand right that's consistent with my thoughts. When I said it wasn't expansion of the house, I meant expansion of the whole house. I think expansion of the wall directly under the render may be the issue, and that's why Ed uses a slip sheet, which I've not heard of but I assume it has some magic that holds the render on the wall but allows limited sideways movement. Of course when that movement occurs the side of the joint needs to be sealed as Jez says.

Complete amateur here but when I render I put my geological background to good use.

So it's shrink cracking as others have suggested. Singletrackmind suggested the mix was too dry, that's a very real possibility. A question, did they buy bags of render which they just chucked in the mixer and added water or did they make their own with bags of sand? Because if they did the quality of the sand is really important. Any clay content and the render will contract as the clay content dries. It's important to use washed sand - plastering sand - and not the cheap sand you'd use for mortar. Use mortar sand and you'll get cracking just like that. I just buy the pre-prepared bags, they have the right components and additives, the only worry then is adding the right right quantity of water to get a workable mix that isn't too dry without being sloppy to use.

The drip plate on the double glazing unit looks too horizontal to me. Both the sill and drip plate should be sloping down. And they've rendered onto it which is inviting water ingress by capiliary action.

How can it be too dry a mix? The harl chips get thrown to a wet coat , if it was even slightly dry they wouldn't inbed whereas is easy to see they are. That is the reason the snot looking waterproof/retarder gets added to the mix , more chance they have added too much of that to make it easy for themselves
K-rend or other silicon based based mixes are normally used flat like the base course , rubbed with a float and finished off with a sponge
Very thin coat and too much cement can cause cracking

Bedtime reading:

Get Advice Sheet 24 Rendering defects from https://www.concrete.org.uk/publications-concrete-advice-sheets.asp

If you're really keen also get Rendering: A practical handbook from https://www.concretebookshop.com/rendering---a-practical-handbook---gcg3-1573-p.asp

concrete made with high alumina cement and reactive aggregate,

You're getting a bit muddled up there. There can be Alkali-silica reaction problems with reactive aggregates and 'normal' cement, see https://www.concrete.org.uk/fingertips-document.asp?id=223

and there can be problems with concrete made with High Alumina Cement, see https://www.concrete.org.uk/fingertips-document.asp?id=795

but they are two very different issues

What is "cheap" mortar sand ?
If it's not fit for purpose it should be be used for anything other than maybe bedding turf or chucked in a skip
Put sand in a bottle , cover it with clean water and shake, any impurities will float to the top of the good sand
Any merchant or b&q selling dodgy building sand would soon get pulled up for it

Not too dry, but drying too fast. As i understood it the water has to stay in the mix for hours to allow the chemical reactions required for strength and adhesion to take place.
This summer we had a month or 2 of really hot dry days. I flaunched in a big chimney pot and wrapped a towel round it.
Every hour it got drenched with 750ml bidon of cold water. Setting cement mixes are exothermic which is desirable
for 6 mth of the year, but less so in 32c.
Possibly a holy trinity of south facing wall, hot weather, maybe the wrong sand or ratio or wetness, some structural expansion not inline with the render. So its cracked, then moisture got in, froze and exasperated the problem.
Still think its gotta come off though.

I m no expert but I ve seen that sort of crazing on some Spanish villas when it rains a lot. Soon as the sun comes they disappear.

I ve watched how Spanish builders work, as I had mine done, it's block, 1st coat cement, finished off with coloured render.

It only rains 20 days a year and we have big overhanging eaves so the top half of walls usually remain dry.

Sorry I can't help any more it must be stressing u out.

It's quite usual to render at 32°C here in SW France, people tend to wait for warm dry days - I am at present. 😉

I've just learned from watching Youtubes, there are lots of them. Most people render onto big insulating bricks or blocks round here. General advice is to thoroughly wet the wall the previous evening, use pre-prepared mix bags rather than faff and risk duff sand, and get the consistency right.

This is the vid I found most useful:

You wouldn't want the French guys on a day rate if you had the whole house to do at that speed, never a good idea to coat all the way down to ground level

My local builders merchants have lots of different types of sand, Redmex. 116 references:

https://www.chausson.fr/materiaux/sables-et-graviers-c-3915

For render you need a pure anagular silica sand, or just buy the ready bags.

I've seen sand in some builders merchants that has attracted my geological interest, lots of fragments of sea shells indicating a high carbonate content and dust that is probably a mix of fine silica, limestone and clay minerals. I didn't buy it but some people must be using it for something.

I use this one for mortar:

https://www.chausson.fr/materiaux/sable-batir-travaux-maconnerie-obra-granulometrie-mixte-sac-35kg-p-451126-1

And this one for concrete

https://www.leroymerlin.fr/produits/materiaux/sable-gravier-et-sel-de-deneigement/sable/sable-a-maconner-0-4-en-sachet-35-kg-82055793.html

Edit: you think that's slow, Redmex, I dream of working that fast. And I render down to the ground without complex.

Another test I do is the taste test, if it's salty I don't buy.

Edit: keep the comments coming, they're food for thought, I've got a lot of rendering to do over the next year and all this chat is useful so thanks to the contributors. I'm listening, Redmex even if it might not seem like it.

Maybe it's beginners luck but all the rendereing I've done so far is holding up well, 20 years for some of it. I'm hoping to do the next lot a bit neater.

There’s a really easy to understand guide on render good practice here and shows the basics for avoiding cracking.

@natrix

You’re getting a bit muddled up there. There can be Alkali-silica reaction problems with reactive aggregates and ‘normal’ cement…  …and there can be problems with concrete made with High Alumina Cement

You're quite right, how embarrassing. I ought to know better than that. Apologies to the OP, it was ASR I was thinking about, nothing to do with HAC.

Maybe we are lucky where I live the natural sand and gravel where there are probably 5 major companies quarrying sand, it gets driven 60 miles to be used by Robeslee for concrete lintols due to the pure quality
Some more dubious concrete lorries are known to bulk out their ready-mix with glass, recycled crushed concrete brick etc, PFA gets used too but it does benefit concrete
The sand I use building and sharp is all washed, no dust or clay and the sharp/concrete sand is exactly how it should be with no fines

Thanks for all the input - very much appreciated.

Its cement render with pebble dash & builder used sand from builders merchant - Selco (yellow & blue bags?) IIRC, rather than pre mixed. We're in Swansea if that makes a difference to possible sand/materials/sun/rain quality?

I've got my timeline slightly mixed up sorry - work was completed in June/July 2021. We noticed damp April 2022 & all of the cracks in Oct 2022. So its all had 18 months or so to get to where it is now.

Plastic/render expanding at different rates makes sense & you can see the pic below where the water is getting in along the window. Not sure why our experienced builder or contractor hasn't done this then..

The work was carried out during the summer with mixed weather = some hot, some wet but it wasn't till several months later that we noticed the cracks. You can see some of them when its dry and all when it rains (water seeping into them taking longer to dry?). The front faces SW & is much worse than the back.

House has double glazing with cavity walls (insulation removed) & minimal loft insulation (I know I know but its full of sh!t from previous owners & will take an age to empty (there are doors, what looks like a work bench etc up there) so I'd imagine temp goes up & down during the day a fair bit, but less so during the summer when its easier to manage than now.

Up on the flat roof we've found a bit of strip of render thats fallen off what looks like the bottom edge above the flashing. Any idea what the staining on the lead flashing is? Besides looking sh!te is it a symptom of the issues

So it looks like its a likely problem with the mix/render & is for the builder to sort.

In an ideal world I think we'd like our money back & go elsewhere (or look at just painting the bricks as suggested) but think thats very very unlikely & I'm expecting, based on conversation so far, a challenge as to whats happened & the cause ie its the house. He's not going to want to do it all again but given how it looks & all of the advice above I can't really see another option we'll be happy with..

The lead needs patination oil applied to stop the staining, no angle bead above the lead makes me think definitely single coat on top of the existing

Good luck, we decided our 100 year old house needed all the render removing.
We don’t have cavity walls and once render was removed it revealed two further layers of paint, then a concrete coating and then finally original brick!!

We’ve had it all sandblasted and about to have it pointed.

We did have some render companies come out who show you the new shiny look you can have and talk about a guarantee but then we also had the pointer tell us we’ve made the right choice as render would stop the house breathing…

It is hard with each person who wants the job saying what you want to hear it seems, very annoying it’s not regulated enough is the industry if you ask me!!

Hello 2bit,
Following on from my last post.
It looks like you may have an issue with condensation building up behind the render.
The marks on the lead flashing look like rust from fixings holding the render beads on or render lath if they used it. When fixing render beads to any external surface you need to be careful which fixings you use. Even galvanised fixings will rust if you damage the galvanising during the fixing process.
If this is condensation building up under the render this can be tricky to overcome, if you seal a house externally you don’t allow the external skin to breathe, this will move the dew point from the face of the render to the nearest point where the temperature changes.
If you have more info on the wall and render build up, a rough sketch showing a section through, I can pass it on to my colleague who is an expert in moisture transfer in buildings.
Hope this helps.

It's a cavity wall so the damp inside wall is almost certainly from condensation. The render waterproofs the outide so there's nowhere for the damp to go.

Forgetting issues with the render for the moment if you want to have dry walls I suggest insulating the wall on the inside with an insulator with a vapour barrier on the inside. The insulation will keep the temperature of the inside surface above dew point so no condensation and the vapour barrier will stop damp getting into the insulation/wall and condensing wherever the dew point falls. You said you need to decorate so now is the time to do it.

In my 30s house with solid walls, insulating on the inside has resulted in the walls being dry both inside and out.

@edthecarpenter
So possibly condensation between brick & render? would that point to the mix not being correct ie it can't breathe? I'll try & get a break down of the profile but IIRC - brick>cavity>brick>misc liquid>mortar#1>mortar#2>dash

I think the misc liquid was put on the bricks before applying the 1st coat

@Edukator
2 of the 3 damp patches are downstairs (living room window as per pics) & above the kitchen window. Both have either obvious cracks in the surround (kitchen) or 'gap turned green' (as per pics above) in the middle of the damp patch ie channels/opportunities for water to get past the render & follow the window frame to get inside (at least to my mind). All patches get worse during & after heavy rain.

We only need to re-decorate the damp patches rather than whole house & have zero funds available for insulating the whole of the inside of the house :/

We're hoping that once dried out we just stain block & paint, plastering if absolutely necessary

Thanks again all - much appreciated