Extensive hairline cracking

[Railto]

Hi
I built a rear extension 18 months ago - full height, from thermalite block. Once complete I had the whole house rerendered. On the advice of the renderer, the new thermalite block section was completely covered with stainless mesh. Once complete, all looked good with no cracking. Over the last 18 months hairline cracks have appeared over the new block work first, but now also over the original house.

On the new extension these cracks are mostly vertical and horizontal and almost regular in frequency across the rendered walls. I have had a structural engineer back out and he has confirmed that there is no movement in the walls.

I can't get hold of the original renderer for love nor money. More cracks are appearing as time passes and I need to get this sorted. Other renders that have come to look at the walls say they havent seen anything quite like it and only offer to rerender the whole house. There are so many cracks that chasing them out, filling and painting is a massive job and will look a real mess.

I need to be sure of the problem before I start throwing money at this. Any ideas?

Cheers

 

[spunky]

I had the same prob on my garage I floated it twice and it was hanging wet ....loads of reasons why it cracks sun, thickness of coats bad mixes too strong too weak wrong sand too much suction too little suction mixed too long ....the list is endless go over it with a thin coat system it's not cheap but it won't crack

 

[jonst64]

are the cracks the approx size and shape of ssmesh sheets ?

 

[Railto]

Thanks - any idea what this is likely to cost?

 

[Railto]

The ssmesh sheets are 800x400 and the pitch of the cracking varies but is between 200-300mm in places. There are what appears to be panels - say 250 wide and half height.

 

[jonst64]

reckon spunkys got the easiest option for ya mate :RpS_thumbup:

 

[spunky]

The best idea would have someone local have a look where are you based mate?

 

[Railto]

Down in Poole. I have had a couple of guys out to look at it and both said they hadn't seen anything quite like it before. I am pretty sure that the underlying building is ok (per structural engineer). However, happy to have anyone to look at it as I need to get it sorted.
Thanks for the help

 

[beddy]

Speak to rich brown, he's your way pal. Does the thin coat systems aswell.

 

[jonst64]

thin coat may not be cheap. but taking ya render off and rerendering wouldnt be cheap either, the render hasnt blown has it ?

 

[lucius]

I take it that there is no cracking on the internals so i would suggest what Spunky said many possible reasons but ime leaning towards that the exmat wasnt fixed properly.

 

[Blade]

I take it that there is no cracking on the internals so i would suggest what Spunky said many possible reasons but ime leaning towards that the exmat wasnt fixed properly.

Think i would agree with lucius , does the render sound drummy , hollow . with the expermet sometimes the render sticks to the expemet and not the blockwork , causing it to be hollow and then over time it will move and crack , ive had the problem , it needs to be well fixed with no movement , even then we still go over it 1st with a slurry coat . No easy fix here i would say

 

[lucius]

And if on my own work if rendered inever use Thermalite or Celcon always Aglite or similar lightweight Clinker block.

 

[S a plastering]

should of used concrete block or simlar you cant get a proper fixing into thermos exter they are too soft i think the mesh is moving about

 

[owls]

mesh it over and use a thin coat system over the top, as others have said,
as long as the substrate is sound doesnt matter if its painted.

 

[Railto]

Many thanks for thoughts. I have been away with work and just got back in the country. All the render is sound, just the cracking that is slowly deteriorating as weather gets into it. I think a thin coat system is the solution.
Cheers,

 

[jack88]

Many of the possible contributary factors suggested, over time i'd expect to create bigger cracks not hairline cracks or grazing...If you've got the same hairline cracking of the render on the house as well after this amount of time and your structural engineer is adamant its not structural, i'd have to say that its highll likely to be something to do with the render itself...Any idea what render was used, what mix?? Prejuming it was S&C 3, 1 and 1??...maybe did'nt use washed sand which had a high clay content...could of been over mixed...could be many factors. It does sounds bizarre to me tho, in that hairline cracks and grazing occurs usually in the first few weeks when its setting if at all....cracks of this nature developing after this amount of time is unusual.

With regards rectification, If it was a few hairline cracks u could chase out the cracks and coat with waethershild....but as its spreading constantly all over the place whats to say this won't continue after chasing out and painting over....i'd leave it a bit longer, if it continues i'd take it back to substrate and go with a highly recommended applicator. maybe even k rend or monocouche, depending on the finish you want.