Render or texture paint on cement board cladding?

[philcvk]

Hi - I'm doing an extension in timber frame and on the outside of the studs I have OSB, breathable membrane (roofing felt), battens and cement render carrier boards. 

 

The final look I need is white render to tie into the rest of the house. The quotes to do the render (thin coat or 6mm silicon) are ££££, and so wondered if it'd be cheaper do beading with 200mm of filler around the edges and then prime and paint everything, using a good grade exterior paint? (probably exterior caulk the joints of the cement boards too).

 

I'd be really interested to hear what others have done on render carrier / cement boards for the final layer. 

 

I've heard issues with thin coat render peeling off the cement boards, and nervous about the paint option that this could be one cheap fix not to make. Would be great to know what other people have done, thanks

Edited Monday at 21:17 by philcvk

[nod]

Unfortunately paint and filler won’t stay on cement board 

Thin coat is fine if it’s done right 

[Nick Laslett]

9 hours ago, nod said:

Unfortunately paint and filler won’t stay on cement board 

Thin coat is fine if it’s done right 

@nod are you sure about this? All my soffits/undercloaking is cement board. It has been up for 2 years, paint seems okay. I’m pretty sure I just followed M.I. on how to paint; use SBR primer. Of course this use case is completely different to what the original post is asking. 
 

https://www.sts-board.com/wp-content/uploads/2024/05/STS-Construction-Board-Product-Leaflet_2024.pdf

 

@Adam2 did you go ahead with painted cement board as you suggested in this thread?

 

 

Edited 16 hours ago by Nick Laslett

[saveasteading]

10 hours ago, nod said:

Unfortunately paint and filler won’t stay on cement board 

There are systems where a netting is applied first, with screw fixings, then the render sticks to the board enough, with the additional support of the mesh. 

Very expensive but it works and I would not advise any other way.

 

Or apply sods law and spill paint or render on it accidentally, as we know that doesn't come off.

[nod]

Think coat render 

we do lots of TF buildings that way 

Sticks like sh## to a shovel

[philcvk]

Thanks, great comments, anyone have a view on doing it now when its sub ten degrees (either paint of thin coat render) or waiting until its warms up in a few months, will either adhere better if I wait a few months or does it not really make too much difference? 

The cement boards have a tarp over them at the moment so not too worried about keeping it like that for a while 

Cheers

 

 

[saveasteading]

1 hour ago, philcvk said:

when its sub ten degrees

Over 4 degrees and it's ok.  If there is cement in the product then it is a chemical reaction, not drying, so this neds to be for at least a day, including early morning frost snaps.

[Mr Punter]

For a couple of jobs I have specced Weber LAC and mesh onto cement type boards, sponge finished then painted.  6mm thick.  It has stood the test of time.  Thin coat beads.  Material costs are about £12/m2.

[philcvk]

thanks, the quotes on thin coat render have back £75-90 / sqm so far (labour and materials, excluding scaffolding), yet checkatrade guide says about £30-70 / sqm, just wondered what everyone's experience with thin coat price is here? the job is 50 sqm, base coat, fibreglass mesh, beading, top coat