Hairline cracks in render - possible cause of water ingress? & possible cure?

8 Jun 2013
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United Kingdom

As the title says, hairline cracks in external render. I wouldn't be bothered normally but there is damp showing inside just above the window where the cracks appear to be.

Is this likely to be the cause of the damp, IE water ingress in through these fine cracks?

What is the best way to repair them? I do not wish to start removing the whole lot and starting again. It doesn't appear to be painted although it possibly could be but with really old white paint. If I was to paint over, will it prevent being able to repair at a later date? IE without removing all the paint? How wide a crack can be 'cured' with paint?

What sort of paint should I be looking for?

All help gratefully welcomed... :)


PS latter photo, the cracks are somewhat larger :(


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why not post some pics giving a larger context of the exterior - and a couple of pics of the interior damp

I dont think its anything too serious from what can be seen.

Have you examined all your external walls for hairline cracks or interior damp signs?

Why was a patch repair made in pic 2?

Thanks for the prompt response. I've attached a few additional photos. The internal 'damp' doesn't show up on the photos but I've circled where it is in the kitchen.

The other photos give a wider perspective on the external as a whole. Unfortunately, I don't have any wider views of the window (it's not the window in the pic). The kitchen window is just around the corner below where the bracket is shown.



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You don't need to post pictures.

Any cracks in render are bad and should be rectified. Those cracks are not hairline.

If the render is hollow and detached, it needs to be hacked off in whole or in patches and redone. Then painted with a suitable flexible paint.

If just cracked, widen the crack and repair, then repaint.

The render needs to be sound right up to the roof, as that's where water can get in and travel downwards - blowing any render below.
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Thank you for the new pics i find them helpful.

Pic 2 of the original pics is showing a few hairline cracks around the soil pipe elbow (i can now see what it is).

The first new pic of the gable also shows hairline cracks - and i would imagine that the clinging foliage is possibly making things worse by holding moisture and perhaps penetrating into any cracks.

The gable roofline (the verge) is difficult to see but it appears that the overhang (there should be an undercloak in place projecting about 50mm - 75mm) is pretty narrow which might be allowing water to creep into the top of the render.

I'd suspect that you have solid walls which will obviously allow easier moisture penetration than cavity walls.

After examining the gable from an extension ladder you will have to decide what next - repair or replace. FWIW: if the paint is not masonry paint then it could be retaining moisture in the wall which in itself will sometimes blow the render.

1. is that a stub of a chimney stack at the gable peak?
2. are there clips on the soil & vent pipes.
3. the long "horizontal" run of the 40mm pipe is retaining leaf debris.
4. what is the object at the upper right hand side of the gable?
RrogerD hi

If possible can you take a very small hammer and gently tap the areas of external cement render and tell us if the sound generated is "Hollow" you could use any implement to gently hit the wall with, even a piece of timber such as a dowel rod.

If you can go over as much of the wall as you can tapping as you go, why? because if the original roughcast render is detached from the brick or block that is the external render has, because of the cracks and the action of frost and the freeze thaw cycle when if rain water has entered behind the render, entering Via the existing cracks, freezes during the winter, as the frozen water thaws is WILL expand by about 9% of its original volume, this WILL force the render away from the brickwork or block work of the external wall, If there are large areas of Hollow sounding external render, then I am sorry but, this is an indication that the entire area of external render has failed and will need to be replaced. There is no way back, patching the cracks in a render that has effectively detached from the brick work or block work is a futile waste of time and money, it will fail again, soon.

As for the internal damp patches? do you know if the external walls are what was termed 9Inch Solid or has the cavity been cavity filled? either of the foregoing will give ruse to internal damp wall problems.

Thanks for all of your replies.

I fully agree with everything that has been said. Looks like there's no option but to hack it off and sort it 'good and proper'.

The internal kitchen is an old annex which I suspect has 9" solid walls. It is a mid-terrace Victorian property. Based upon the above, I suspect that the damp is creeping through due to water running behind the render. Oh dear :(

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