My render

[Jason L]

Afternoon,

 

Im trying to work out if and where i will need movement joints in my render, i have tried talking to K render and they wasn't much help tbh.

The CGI of the house is attached,  it will be K render thin coat render system on a render carrier board on the timber frame.

Has anyone any ideas if and where i should put some ?

thanks

[nod]

Every 10 metres 

Block-work also 

It will be on your working drawings 

Edited December 9, 2020 by nod

[Jason L]

51 minutes ago, nod said:

Every 10 metres 

Block-work also 

It will be on your working drawings 

Will it be the same for on a TF then ?

it will be on the drawings when then are done ?

[LA3222]

@nod beat me to it. There's not much point in having expansion joints if there isn't one in the blockwork. What should happen is expansion joints in the blockwork, an expansion bead goes over that and render goes up to the expansion bead.

 

Manufacturers tend to be no help as they probably dont want to be at risk of liability. I asked Johnstones the same questions for my render, they said ask the architect, the architect said ask Building Control who said to ask the structural engineer designing the walls of the house - really!

 

In the end I told the brickies to put expansion joints in and where to do it (following NHBC guidance) and then the renderers put the expansion beads over them and the rest is history.

[LA3222]

3 minutes ago, Jason L said:

Will it be the same for on a TF then ?

it will be on the drawings when then are done ?

Yarp. I have SIP inner skin, blockwork outer - I got Ancon debonding ties (every course with blockwork) and the foam expansion joint filler. Once brickies done I went over the gap with White silicon to fill it it (not full depth, just over the top of the foam). Rendered came and then put a bead over it etc.

 

Try to line them up with gutter downpipes to hide them.

[LA3222]

58 minutes ago, nod said:

 It will be on your working drawings 

You'd think so wouldn't you, they weren't on mine though even though the frontage of the house is a 15m run of blockwork!

[MarkyP]

I have none on my rendered EWi which was covered with baumit basecoat and thincoat silicate top coat. Baumit tech rep said movement beads are pointless unless there is an underlying structural movement joint, it's one of those old industry habits that hadn't died out yet. This is obviously one opinion but which they warrant - no cracks so far along an 18m wide single storey elevation. 

 

If the underlying structure doesn't have a movement joint then render will expand/contract monocoque with the substrate, if the substrate cracks then a movement joint only in render won't help, might be in the wrong place as no one will have told the blockwork where to crack ? so the logic is if a movement joint is needed, put in render and substrate, not just one or the other.

 

Talk to render supplier about their requirements, designers throw in movement joints in render by habit, may not be necessary. They are ugly, as are the plastic beads used with monocouche, my pref is silicate (mineral) thincoat, no joints or exposed plastic beads. 

[MarkyP]

I have none on my rendered EWi which was covered with baumit basecoat and thincoat silicate top coat. Baumit tech rep said movement beads are pointless unless there is an underlying structural movement joint, it's one of those old industry habits that hadn't died out yet. This is obviously one opinion but which they warrant - no cracks so far along an 18m wide single storey elevation. 

 

If the underlying structure doesn't have a movement joint then render will expand/contract monocoque with the substrate, if the substrate cracks then a movement joint only in render won't help, might be in the wrong place as no one will have told the blockwork where to crack ? so the logic is if a movement joint is needed, put in render and substrate, not just one or the other.

 

Talk to render supplier about their requirements, designers throw in movement joints in render by habit, may not be necessary. They are ugly, as are the plastic beads used with monocouche, my pref is silicate (mineral) thincoat, no joints or exposed plastic beads. 

[MarkyP]

Looks like others beat me to it, must type faster! 

[Jason L]

13 minutes ago, MarkyP said:

Looks like others beat me to it, must type faster! 

Thank you,  it looks like you posted the same twice haha

 

Im getting nervous as i watched a presentation on it yesterday with the same construction as mine and they said the timber frame will move as it dries out etc so they are needed.  However they didn't really go into where,  and it just seemed like a selling their render product presentation in the end.   I have asked K rend to email me some tech info which they haven't done.

[LA3222]

17 minutes ago, Jason L said:

Thank you,  it looks like you posted the same twice haha

 

Im getting nervous as i watched a presentation on it yesterday with the same construction as mine and they said the timber frame will move as it dries out etc so they are needed.  However they didn't really go into where,  and it just seemed like a selling their render product presentation in the end.   I have asked K rend to email me some tech info which they haven't done.

Ah, I see your issue - most of us are talking blockwork but you have carrier boards. Someone on here had issues with billowing I think the term is of their carrier boards which was visually very obvious so may be worth finding that thread - if memory serves me correctly it was @Bitpipe but I may be wrong?‍♂️

 

I didn't go to much into it at the time as it wasn't an issue i would have.

 

I'd say the carrier board manufacturers are the ones to speak to if you haven't done so already?

 

Like @MarkyP says, there is a good chance you'd be fine without them but its up to you to whether you're willing to accept that risk - albeit small.

[Mr Punter]

Nobody read the original thread very carefully.  You may want to take advice from the carrier board people.

 

The Bluclad BBA certificate says:

 

13.7 Horizontal movement joints must be provided at every floor to accommodate vertical shrinkage of up to 6 mm in the timber frame and to follow movement joints in the substructure. For steel-frame structures, reference should be made to the Structural Engineer’s details for detection at floor level and movement joints in the substructure.
13.8 Vertical movement joints should be provided at the required intervals. The actual spacing and position of the joints will be determined by the shape of the area to be rendered and should coincide with movement joints in the structure and allow for the same degree of movement.

[Bitpipe]

I have a Parex render system (topcoat / base coat / mesh / base coat / renderboard / batten) on a TF wall and no expansion gaps were specified.

 

I have had a lot of issues - render pillowed up and boards under are now cracked. Company committed to fix it.

 

Initially I was worried that it was due to no expansion gap (which were not in design) but then find out none were needed.

 

Instead it's incorrect fixing of battens to structural timber in the frame so they were able to pull through the outer skin.

[Jason L]

10 minutes ago, LA3222 said:

Ah, I see your issue - most of us are talking blockwork but you have carrier boards. Someone on here had issues with billowing I think the term is of their carrier boards which was visually very obvious so may be worth finding that thread - if memory serves me correctly it was @Bitpipe but I may be wrong?‍♂️

 

I didn't go to much into it at the time as it wasn't an issue i would have.

 

I'd say the carrier board manufacturers are the ones to speak to if you haven't done so already?

 

Like @MarkyP says, there is a good chance you'd be fine without them but its up to you to whether you're willing to accept that risk - albeit small.

Yes cheers.     ill have a look for that thread laters.  i cant remember if i spoke to the carrier board manufacture, but i can try them.   This presentation that i watched put up a couple of scare pictures such as this one ! 

[Jason L]

4 minutes ago, Bitpipe said:

I have a Parex render system (topcoat / base coat / mesh / base coat / renderboard / batten) on a TF wall and no expansion gaps were specified.

 

I have had a lot of issues - render pillowed up and boards under are now cracked. Company committed to fix it.

 

Initially I was worried that it was due to no expansion gap (which were not in design) but then find out none were needed.

 

Instead it's incorrect fixing of battens to structural timber in the frame so they were able to pull through the outer skin.

Thank you,  can i ask roughly what size render panels you have,  how was the battens fixed and how should they be fixed, so that i can make sure it is right.

[Russell griffiths]

@Red Kite have just had theirs done and they had an expansion joint horizontally around the whole house, it was something to do with the guarantee of the render. 

Work out who is going to warranty the installation, then it’s down to them to specify the methods. 

[nod]

20 hours ago, nod said:

Every 10 metres 

Block-work also 

It will be on your working drawings 

TF especially 

we put breaks in the cement board with expansion joints Usually under and above a window 

 

[Bitpipe]

2 hours ago, Jason L said:

Thank you,  can i ask roughly what size render panels you have,  how was the battens fixed and how should they be fixed, so that i can make sure it is right.

 

They were standard 2400x1200 boards. The TF outer wall is panelvent (heavy duty MDF) covered in building paper but behind that are vertical structural ribs. They are what the panelvent attaches to and the frame manufacturer stapled the building paper to the panelvent with vertical seams of staples lined up with the ribs.

 

The ribs are not perfectly uniform but the render team put the battens up at 400 centres. This meant that the majority of them are just screwed into MDF and not solid timber.

 

The boards will want to expand and contract in heat/cold and the weight of the system will further pull on the battens with the result they have come loose from the underlying TF wall and are not providing any resistance to the board movement.

 

There may also be an issue with the boards themselves, tbc.

 

It must be said, the Parex system has flexed and bowed under the stress but shows no sign of failure itself (cracks etc) but obviously looks crap.

 

So understand from your TF contractor WHERE the renderboard battens need to be attached to get proper purchase on the frame.

 

Then MAKE SURE thats where they get attached by the render contractor.

 

I'd also advise getting an anti fungal coating if offered as it does go a bit green/yellow in winter where the prevailing wind hits it.

 

And understand what your warranty provision is from the render contractor.

 

Hugh

[Jason L]

19 minutes ago, Bitpipe said:

 

They were standard 2400x1200 boards. The TF outer wall is panelvent (heavy duty MDF) covered in building paper but behind that are vertical structural ribs. They are what the panelvent attaches to and the frame manufacturer stapled the building paper to the panelvent with vertical seams of staples lined up with the ribs.

 

The ribs are not perfectly uniform but the render team put the battens up at 400 centres. This meant that the majority of them are just screwed into MDF and not solid timber.

 

The boards will want to expand and contract in heat/cold and the weight of the system will further pull on the battens with the result they have come loose from the underlying TF wall and are not providing any resistance to the board movement.

 

There may also be an issue with the boards themselves, tbc.

 

It must be said, the Parex system has flexed and bowed under the stress but shows no sign of failure itself (cracks etc) but obviously looks crap.

 

So understand from your TF contractor WHERE the renderboard battens need to be attached to get proper purchase on the frame.

 

Then MAKE SURE thats where they get attached by the render contractor.

 

I'd also advise getting an anti fungal coating if offered as it does go a bit green/yellow in winter where the prevailing wind hits it.

 

And understand what your warranty provision is from the render contractor.

 

Hugh

i see and understand now,  thank you very much 

J

[nod]

4 hours ago, LA3222 said:

You'd think so wouldn't you, they weren't on mine though even though the frontage of the house is a 15m run of blockwork!

Not good 

[ProDave]

5 hours ago, Jason L said:

Yes cheers.     ill have a look for that thread laters.  i cant remember if i spoke to the carrier board manufacture, but i can try them.   This presentation that i watched put up a couple of scare pictures such as this one ! 

 

What is the back story there?  What was the cause for the failure?  Link to anything describing it (I still have some issues with my rendering, also the Baumit system)

[Jason L]

52 minutes ago, ProDave said:

 

What is the back story there?  What was the cause for the failure?  Link to anything describing it (I still have some issues with my rendering, also the Baumit system)

Sorry I don’t know anything about that, other than it was one of the photos the presentation showed of issues that is caused without movement joints.  What are your issues ? 

[SuperJohnG]

Ive not got any expansion joints shown on my drgs either currently,  which is render on renderboard on SIPS. Id prefer not to have them also

 

I've not quite figured out how to ensure I avoid @Bitpipes scenario as SIPS only have splines which will be further apart than battens spacing. 

 

I'd be interested to see how others mount their renderboard whether its horizontally or vertical. 

[Bitpipe]

9 hours ago, SuperJohnG said:

Ive not got any expansion joints shown on my drgs either currently,  which is render on renderboard on SIPS. Id prefer not to have them also

 

I've not quite figured out how to ensure I avoid @Bitpipes scenario as SIPS only have splines which will be further apart than battens spacing. 

 

I'd be interested to see how others mount their renderboard whether its horizontally or vertical. 

 

Our renderboard was fixed horizontally in a brick bond style. How far apart are the splines? At a minimum, battens need to be fixed to these as I'm guessing the rest of the SIP panel is OSB?

 

Is there a fixing to OSB that will give you more mechanical purchase?

 

I found this resource but as ever it passes the buck .... (page 82)

 

https://www.thesipcompany.com/assets/downloads/sta-sips-pocket-guide-aug2016.pdf

 

Corrosion resistant fasteners from the cavity batten to the SIP panel are to be specified by the building designer so that they are suitable for both the loads and the SIP outer board thickness capacity. 

[Bitpipe]

Our render contractor MD is back on site tomorrow, 5 years since the system went on, and hopefully we get resolution to this never ending issue - will update my other thread with any interesting nuggets but the incorrectly applied battens to appear to be the smoking gun.