External wall insulation over pebble dash

erooney

Looking for your thoughts on installing EWI over a dash finish. How does this affect the performance of the system? I'm wondering if it is a big problem that there will be an air gap between the wall and the insulation due to the dash? Will this allow the heat to escape easily? Also, does the dash support then insulation adequately as the boards are likely to sit on the high points of the stone? Thanks.

sydthebeat

the EWI must be applied to a flat surface

erooney

sydthebeat wrote: »

the EWI must be applied to a flat surface

Ok, so what are my options? Removing the render would be torture I imagine.

MicktheMan

sydthebeat wrote: »

the EWI must be applied to a flat surface

...or installed such that there is no thermal looping between boards at the back of the insulation. One method of achieving this is to "butter" the edge of the board with a good thick adhesive before applying the board to the wall.

erooney

MicktheMan wrote: »

...or installed such that there is no thermal looping between boards at the back of the insulation. One method of achieving this is to "butter" the edge of the board with a good thick adhesive before applying the board to the wall.

Thanks Mick, I have been looking into renting an sds drill with a chisel to remove it but I am a bit reluctant to start doing 140 sqm of wall. Maybe it's a bit less if I take the windows out of the equation but it's still no easy task. Whatever I do, I don't want to spend money on a new insulation system and for it to not work properly. I can ask the installers I have quotes from if they can / will do what you describe.

fozz10

yep the coat of base-coat or adhesive should sort that. don't go hacking off pebble dash, maybe if it was a heavy wet dash but dry dash should be grand with the glue.

erooney

fozz10 wrote: »

yep the coat of base-coat or adhesive should sort that. don't go hacking off pebble dash, maybe if it was a heavy wet dash but dry dash should be grand with the glue.

Yeah it's 50 year old wet dash on a cavity block wall, house was built like that. Its going to be a pain in the arse to insulate. Don't buy an old house, nothing is straightforward!

antiskeptic

erooney wrote: »

Yeah it's 50 year old wet dash on a cavity block wall, house was built like that. Its going to be a pain in the arse to insulate. Don't buy an old house, nothing is straightforward!

Maybe use the 'trickiness' of the job to sift through contractors. If they don't see the issues then they aren't fit for purpose. The one who can explain the need for the solution you find here (or elsewhere) yourself, is more likely your man.

sydthebeat

Make sure not to install it in such a manner as to make any guarantee useless ie installation not in accordance with manufacturers specifications.

The EWI must be installed on a flat surface, how you make that surface flat is up to you.

The way i see it youve two choices. either hack off the wet dash, or apply a render over the wet dash to make it flat.
Ive seen wet dash that could be 20 - 30mm off the wall surface, i wouldnt like to be trying to make that up by lathering adhesive on the back of the insulation!!!


for example, this system indicates its tolerance as

Substrate Dimensional Tolerances: Flat within 1/4 inch (6.4 mm) within any 4 foot (1219 mm) radius.

so thats a 0.005% deflection.

i can pretty much guarantee that you will not be able to install EWI to that degree of accuracy over existing wet dash finished wall.

BryanF

It's down to the system guarentee. Some argue that sealing each insulation piece on all edges is acceptable. Study the bigger European 'systems' - your not ready to deal with installers.

erooney

Thank you for your replies. I have a clearer picture now about what is required.

1) chipping the wet dash and putting insulation directly onto flat block.
2) rendering the building to a level surface for the insulation.
3) buttering the back of the boards with adhesive.

I might pick your brains a bit here, Are there any other systems that are effective? I have the inside of the house stripped out. I thought about insulated plasterboard but I have 4 solid internal walls adjoining external walls not including the party wall. I was worried about cold bridging / condensation. I had made the decision to go external to but might need a fall back if this render doesn't want to come off without destroying the wall in the process.

bulleyes

Im currently in the exact same situation. Could I ask how you solved your issue and if your happy with the result?

erooney wrote: »

Looking for your thoughts on installing EWI over a dash finish. How does this affect the performance of the system? I'm wondering if it is a big problem that there will be an air gap between the wall and the insulation due to the dash? Will this allow the heat to escape easily? Also, does the dash support then insulation adequately as the boards are likely to sit on the high points of the stone? Thanks.

FishOnABike

Are there suitable external cork mix external render systems that might be suitable to apply over the pebbledash and leave a smooth finish?

lucat

I'm considering buying an old house with wet dash, probably 50 years old or so. I want to get EWI but one concern I'd have is that the dash will obviously have to be 100% dry and so will any waterlogged cracks from settlement etc. How much of a problem will this be?!

MicktheMan

lucat wrote: »

I'm considering buying an old house with wet dash, probably 50 years old or so. I want to get EWI but one concern I'd have is that the dash will obviously have to be 100% dry and so will any waterlogged cracks from settlement etc. How much of a problem will this be?!

Imo, shouldn't be an issue assuming of course the settlement has stopped. I would always recommend using a breathable ewi system in any case.