Hi to all in the forum introducing myself - I'm not a plasterer or a renderer but managing a project, currently building a single storey annex. Thanks in advance for any help.
The insulation on the annex has been incorrectly installed, and impossible to remove and correct. Basically 100mm cavity, 90mm insulation, should have been taped and held back against the internal wall, it hasn't.
And to top that the insulation fits together with a lip (think interlocking reversed L shapes), and the lip is facing towards the roof instead of towards the base of the wall. Should water ingress through the render, then the concrete block, it could then run down into the insultion, through the upside down joints, into the inside wall, creating damp spots.
To make matters worse, mortar snots on the inside thermal block work are pushing the insulation into direct contact with the outside concrete block. You wouldn't think there was any gap, and 10mm is not a lot to start with.
The building inspector has stopped work and wants a solution - hopefully one that does not involve removing the internal walls and re-doing the insulation job (we are roof plate level). Not his fault - he is just doing his job.
I'm thinking no water ingress past the render = no water ingress to the inside wall and hopefully a happy building inspector and client. So to my questions: Initially...
Could we tank the outside walls with a 100% waterproof tanking membrane, that you can then render over?
Assuming (hoping) yes... then 2 questions please:
1. What tanking membrane system solution would be best? (there are quite a lot, some with mesh etc. thinnest possible preferred as there is raised stone work on the corners (around 25mm) so wuldn't want the top coat to be higher than the stone work.
2. Is there a specific render that should be used with the above that I can discuss with the plasterer?
Asking on here, as having an idea myself will ensure I can first OK with the building inspector, and get the right materials and the right plasterer for the job.
Thanks in advance for any help / advice - hopefully an interesting one that helps others on the rare occasions an outside wall would need to be rendered over a tanking membane. Did consider just plenty of SBR but manufacturer states it's not actually waterproof.
Best regards
Paul
The insulation on the annex has been incorrectly installed, and impossible to remove and correct. Basically 100mm cavity, 90mm insulation, should have been taped and held back against the internal wall, it hasn't.
And to top that the insulation fits together with a lip (think interlocking reversed L shapes), and the lip is facing towards the roof instead of towards the base of the wall. Should water ingress through the render, then the concrete block, it could then run down into the insultion, through the upside down joints, into the inside wall, creating damp spots.
To make matters worse, mortar snots on the inside thermal block work are pushing the insulation into direct contact with the outside concrete block. You wouldn't think there was any gap, and 10mm is not a lot to start with.
The building inspector has stopped work and wants a solution - hopefully one that does not involve removing the internal walls and re-doing the insulation job (we are roof plate level). Not his fault - he is just doing his job.
I'm thinking no water ingress past the render = no water ingress to the inside wall and hopefully a happy building inspector and client. So to my questions: Initially...
Could we tank the outside walls with a 100% waterproof tanking membrane, that you can then render over?
Assuming (hoping) yes... then 2 questions please:
1. What tanking membrane system solution would be best? (there are quite a lot, some with mesh etc. thinnest possible preferred as there is raised stone work on the corners (around 25mm) so wuldn't want the top coat to be higher than the stone work.
2. Is there a specific render that should be used with the above that I can discuss with the plasterer?
Asking on here, as having an idea myself will ensure I can first OK with the building inspector, and get the right materials and the right plasterer for the job.
Thanks in advance for any help / advice - hopefully an interesting one that helps others on the rare occasions an outside wall would need to be rendered over a tanking membane. Did consider just plenty of SBR but manufacturer states it's not actually waterproof.
Best regards
Paul
