External rendering over cement board. PLEASE HELP

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Dimmy

New Member
Hi guys. I'm new to the forum so hello .

We have recently put a new timber extension to the side of our house.

We have used cement render boards to try and make it as lightweight as possible (white ones like aqua panels 12mm thick)

My plasterer is a bit old school and he sbr'd the surface of the board and put a base/ scratch coat of cement on and then a top coat.

Needless to say it has all fallen off as the base coat hasn't adhered to the cement board.

We are now not sure what to use to render the boards and reluctant until we get some advice.....

Any ideas please??
 

Dimmy

New Member
IMG_2173.JPG
 

algeeman

It’s A Boy
Hi guys. I'm new to the forum so hello .

We have recently put a new timber extension to the side of our house.

We have used cement render boards to try and make it as lightweight as possible (white ones like aqua panels 12mm thick)

My plasterer is a bit old school and he sbr'd the surface of the board and put a base/ scratch coat of cement on and then a top coat.

Needless to say it has all fallen off as the base coat hasn't adhered to the cement board.

We are now not sure what to use to render the boards and reluctant until we get some advice.....

Any ideas please??

eml cement boards first.
and stop telling porkies you done it yourself !!!!
 

Dimmy

New Member
Lol we put the boards on. They are now yellow in colour tho from the sbr. And honestly my plasterer done it. I'm a carpet fitter and haven't the first clue
 

Dansouthcoast84

Private Member
Lol we put the boards on. They are now yellow in colour tho from the sbr. And honestly my plasterer done it. I'm a carpet fitter and haven't the first clue

nice looking extension.

sand and cement isnt compatible with cement board.

if you get you or your plasterer to look up thin coat render you will see the difference.

these renders are warranted and.designed for these build being thinner lighter and flexible to take the movement of the timber.
 

passi

Member
Needs a decent primer coat to help base coat adhere properly. Then let this cure.

Sent from my SM-G900F using Tapatalk
 

Dimmy

New Member
Cheers lads.

Any idea what primer to use on the boards. I've done a little research and it sounds like krend hp12 with a tc15 top coat looks like a way to solve this????have you guys used it??

Also the garden wall was done buy the old man who had some surplus cement
 

malc

TPF Special Forces
Cheers lads.

Any idea what primer to use on the boards. I've done a little research and it sounds like krend hp12 with a tc15 top coat looks like a way to solve this????have you guys used it??

Also the garden wall was done buy the old man who had some surplus cement

i am sure that you have lost the key from the boards when sbr was applied. then rendered in sand and cement.
yours is only a small job so i would over board, then employ someone qualified to carry out the work.
were is your property they may be someone on the forum that can carry out this work for you.
 

Spray

Well-Known Member
Cheers lads.

Any idea what primer to use on the boards. I've done a little research and it sounds like krend hp12 with a tc15 top coat looks like a way to solve this????have you guys used it??

Also the garden wall was done buy the old man who had some surplus cement
Seems like the lads slat
Put some parex microgobetis on the boards before your basecoat
thats a bad idea
 

Spray

Well-Known Member
Hi guys. I'm new to the forum so hello .

We have recently put a new timber extension to the side of our house.

We have used cement render boards to try and make it as lightweight as possible (white ones like aqua panels 12mm thick)

My plasterer is a bit old school and he sbr'd the surface of the board and put a base/ scratch coat of cement on and then a top coat.

Needless to say it has all fallen off as the base coat hasn't adhered to the cement board.

We are now not sure what to use to render the boards and reluctant until we get some advice.....

Any ideas please??
Don't think much to the advise you have recieved to be honest don't prime the boards and don't use hp12 !
 

Jrend

Active Member
i would use parex maitie or weber lac adhesive coat with mesh bedded in 4/6 mm as stated above.
 

Green trowel

New Member
Hi mate my builder done this a few jobs back he checked it online advice was apply skrim to joints then cover with a Webber tile adhesive like tape and jointing wen that dries apply sand and cement scratch coat then allow to cute then apply top coat I was a bit sceptical but it's still there with no problems I think if you got issues it might be worth putting elm or rib lath on then render
 

Spray

Well-Known Member
Hi mate my builder done this a few jobs back he checked it online advice was apply skrim to joints then cover with a Webber tile adhesive like tape and jointing wen that dries apply sand and cement scratch coat then allow to cute then apply top coat I was a bit sceptical but it's still there with no problems I think if you got issues it might be worth putting elm or rib lath on then render
That can't be right ! Nobody would advise that surley ?
 

Tim B

New Member
Hi guys. I'm new to the forum so hello .

We have recently put a new timber extension to the side of our house.

We have used cement render boards to try and make it as lightweight as possible (white ones like aqua panels 12mm thick)

My plasterer is a bit old school and he sbr'd the surface of the board and put a base/ scratch coat of cement on and then a top coat.

Needless to say it has all fallen off as the base coat hasn't adhered to the cement board.

We are now not sure what to use to render the boards and reluctant until we get some advice.....

Any ideas please??

Pretty sure thes carrier boards are only for thin coat Polymer render mixes ! ie K rend - or pro rend
If you wanted sand and cement finish should have been Stanless steel EML sub base
 

Spray

Well-Known Member
Pretty sure thes carrier boards are only for thin coat Polymer render mixes ! ie K rend - or pro rend
If you wanted sand and cement finish should have been Stanless steel EML sub base
Can have any finish he liked on to this backing ! Smooth / scraped etc it’s just down to products used ! K rend and pro rend are brands not a specific product
 

Arti

Well-Known Member
Hi guys. I'm new to the forum so hello .

We have recently put a new timber extension to the side of our house.

We have used cement render boards to try and make it as lightweight as possible (white ones like aqua panels 12mm thick)

My plasterer is a bit old school and he sbr'd the surface of the board and put a base/ scratch coat of cement on and then a top coat.

Needless to say it has all fallen off as the base coat hasn't adhered to the cement board.

We are now not sure what to use to render the boards and reluctant until we get some advice.....

Any ideas please??
Get a spec from which ever render supplier you want to use. saves guessing and getting through different opinions
 
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