External Wall Insulation (how to do?)

happypie

I am in process of getting external Wall Insulation done.
My neighbour has done it couple of years ago and advised me that I take off existing rendering, go to brick level, spray/wash bricks and then put Insulation board.
This sounds like a good idea given that I don't have enough gap between neighbour house, window sill, door frame etc.

However my installer's policy say that they will do 'hammer test' and rendering comes off then only they will take off rendering.
I don't think my existing rendering is this weak that it will come off easily.
Being a green grant job, installer is not very flexible and approachable easily.

Do you think its a bad idea to put Insulation on top of existing rendering? I am thinking of giving up on grant and getting it done privately the way I want - but just want to confirm if taking rendering off really is the best way.
(BTW installer has agreed to put 30mm kingspan instead of 50mm eps board when I showed concern about narrow gap).

Thanks.

FreeBear

Lumpy bumpy pebbledash ?

Yes, strip the top layer off or put a parging coat on top to level & smooth it off. Depending on the age & type of render, it may be a right pig to get off, or it may just fall off.

I'm in the process of removing some piggin !!!!!! pebbledash here. With an small air chisel, the top layer is coming off pretty easily, leaving a very hard & tough base coat. The bits missed with the air chisel are cleaned up with a diamond cup wheel on the end of an angle grinder. It is very messy work, and is a slow process. Understandable why your installer wouldn't want to remove the render as it would probably take him most of the week - Either costing you extra or taking a big chunk out of his profit.

EssexExile

It goes over the existing render around these parts.

Jeepers_Creepers

Why the need or desire to remove pebbledash or render first? Unless, of course, it's so loose that it could cause delaminating issues later on.

happypie

FreeBear said:

Lumpy bumpy pebbledash ?

Yes, strip the top layer off or put a parging coat on top to level & smooth it off. Depending on the age & type of render, it may be a right pig to get off, or it may just fall off.

I'm in the process of removing some piggin !!!!!! pebbledash here. With an small air chisel, the top layer is coming off pretty easily, leaving a very hard & tough base coat. The bits missed with the air chisel are cleaned up with a diamond cup wheel on the end of an angle grinder. It is very messy work, and is a slow process. Understandable why your installer wouldn't want to remove the render as it would probably take him most of the week - Either costing you extra or taking a big chunk out of his profit.

No its not pebbledash.
Its rendering, but not smooth one, old style - not sure what its called. Around 100 years old house.

OilyByker

both S&C and pebblewdash are based on concrete, if there is no damp in the buiilding, no need to remove (Unless its already blown). 
Your EWI is going to deal the walls anyway, but remember you DO NOT HAVE TO have flat white render finish over EWI. There a other options to have brickFX render or stoneFX finishes. not evevryone wants whire render, but the green deal contractors want easy and fast... lol 

happypie

OilyByker said:

both S&C and pebblewdash are based on concrete, if there is no damp in the buiilding, no need to remove (Unless its already blown). 
Your EWI is going to deal the walls anyway, but remember you DO NOT HAVE TO have flat white render finish over EWI. There a other options to have brickFX render or stoneFX finishes. not evevryone wants whire render, but the green deal contractors want easy and fast... lol 

There used to be damp.
During renovation, I did DPC (damp proofing course), and new rendering from inside. So far not seen any sign of damp in 2 years or so.
Its difficult to say how strong my current rendering is, its not coming off definitely, but not really sure how strong it should be or how should I test it?