Crumbling mortar - advice please.

Robert Allen

If anyone could advise me here id appreciate it.

I noticed a few horizontal hairline cracks in external wall at radon level. I removed some of the plaster and i see that the mortar between the block and radon barrier is soft and crumbling about 20 - 25mm into the joint.

Can anyone tell me what the cause is here? There doesnt seem to be rising damp and the footings/ foundation dont seem to have sank.

I dont know if the mortar got weak and caused the plaster to crack or if the plaster cracked first for some reason and water got in to damage the mortar.

Has anyone seen this happen before?

Thanks all.

Advice is appreciated.

Rob.

Calahonda52

any pictures?

sydthebeat

Sounds like no weep holes above the DPC / radon... So water simply pools there

Robert Allen

If anyone could advise me here id appreciate it.

I noticed a few horizontal hairline cracks in external wall at radon level. I removed some of the plaster and i see that the mortar between the block and radon barrier is soft and crumbling about 20 - 25mm into the joint.

Can anyone tell me what the cause is here? There doesnt seem to be rising damp and the footings/ foundation dont seem to have sank.

I dont know if the mortar got weak and caused the plaster to crack or if the plaster cracked first for some reason and water got in to damage the mortar.

Has anyone seen this happen before?

Thanks all.

Advice is appreciated.

Rob.

sydthebeat

is your dpc level at ground level??????

Robert Allen

sydthebeat wrote: »

is your dpc level at ground level??????

No the radon barrier is just above the level of the paths, dpc is a block higher.

Thanks for the reply.

Does this sound right?

Robert Allen

sydthebeat wrote: »

Sounds like no weep holes above the DPC / radon... So water simply pools there

Thanks for reply, am i right in thinking water shouldnt be in the cavity to begin with? Its a block wall internal and external so weep holes were not put in.

Robert Allen

Sorry guys - ive been having internet issues also so i didnt see your replies earlier and didnt realise i posted the initial question twice.

I appreciate your input on this. Been having a few sleepless nights on it to be honest.

Thanks again.

Robert Allen

This is a drawing of where the problem is. The ext render is a notable brand and contains "waterproof" silicone. Thanks lads,

10-10-20

Was the house rendered with a standard render mix in the past and was the k-rend applied as an upgrade later? What age is the house?
I'm just trying to work out why the weak line is so inconsistent/wavy. I wonder was the mortar or old render was weakened by drying out too soon after it was applied.
Pull back a bit and take another photo?

Robert Allen

10-10-20 wrote: »

Was the house rendered with a standard render mix in the past and was the k-rend applied as an upgrade later? What age is the house?
I'm just trying to work out why the weak line is so inconsistent/wavy. I wonder was the mortar or old render was weakened by drying out too soon after it was applied.
Pull back a bit and take another photo?

House is build 5 years, plastered a year and a bit or maybe 2 years after walls were built. Scratch coat put on and then k rend after that all at the same time - fairly sure the scratch coat was left to dry for a week or so.

The blockwork and mortar was definitely ok prior to plaster being put on. I never seen water in the cavity even before it was plastered so i really dont know

Ill try get better pics in the morning.

I appreciate the advice on this, thank you.

bfclancy

Robert Allen wrote: »

Thanks for reply, am i right in thinking water shouldnt be in the cavity to begin with? Its a block wall internal and external so weep holes were not put in.

there are never weep holes put in concrete block rendered walls

Robert Allen

10-10-20 wrote: »

Was the house rendered with a standard render mix in the past and was the k-rend applied as an upgrade later? What age is the house?
I'm just trying to work out why the weak line is so inconsistent/wavy. I wonder was the mortar or old render was weakened by drying out too soon after it was applied.
Pull back a bit and take another photo?

Heres a view from further back, this wall is North facing so paths are a little rough after the winter but the cracks are on other sides of house also, starting at the corners and going for a 2-metres around the corners. Ive only noticed them a few weeks back so i cant say how long theyve been there. Id say rain and frost didnt help but id love to know why its happening.

upupup

weep holes are not needed and water in the cavity is not the problem.
If the blocks were laid in winter and it may be frost damage to the mortar and if laid in summer it could be because they dried out too quickly but its not something to worry about as its only the outside 20mm mortar.Your house is going nowhere.
There is no real bond between the blocks above radon level and the blocks underground.The house just sits on the plastic barrier,this is the same in every house so any subsidence will show there and this point is usually hidden by the footpath.

Robert Allen

upupup wrote: »

weep holes are not needed and water in the cavity is not the problem.
If the blocks were laid in winter and it may be frost damage to the mortar and if laid in summer it could be because they dried out too quickly but its not something to worry about as its only the outside 20mm mortar.Your house is going nowhere.
There is no real bond between the blocks above radon level and the blocks underground.The house just sits on the plastic barrier,this is the same in every house so any subsidence will show there and this point is usually hidden by the footpath.

That post will help me sleep better tonight, thanks. Ill keep an eye on it and get a structural engineer if it seems to get any worse.

Does anyone reckon I would need to take the plaster off, scrape and re-point the mortar and re-render it?

Thanks again for taking time to respond.