Which render? K Rend/ Weber or painter ?

[Colin Shaw]

I am finalising a quote from my builder for a new build. Walls are block and insulation on exterior with a render over thus.

We had always considered using k-rend or Weber finish but the builder is far keener to do a sand/cement finish which will require painting.

His reasoning is that he believes Weber etc will turn green (algae/moss?) and require annual jet washing.

Would love to hear opinions on this and peoples reasoning for choosing their own finish and experiences with annual maintenance.

many thanks 

[Temp]

Can't comment on the choice of render but i do know that a good render job needs attention to details with things like drip beads in the right places. Some render is/isn't approved for use below the dpc etc. Perhaps worth googling for guides.

[nod]

I did ours in K four years ago and we are surrounded by tree 

Still looks like the day I did it 

No need to get wash alga 

Simply spray Algacide 12-1 with a hand sprayer Let the rain do the rest 

 

K tends to be a better colour match than Webber 

[SuperJohnG]

Following this with interest. I'm planning a k rend silicone render. Have heard OK things about JUB render though.

[nod]

Very little difference between most of the through coloured renders 

Other than the after sales service 

K Rend are miles ahead of Webber

[Colin Shaw]

Thanks for the replies. I am keen to stick with original k-rend plan just needed some genuine feedback to discuss with builder... ultimately it’s my choice of course!

[Evs]

I’m in the same boat and have also been told that k rend is more likely to be affected by algae. But the 2 people that have said this to me have no theory to back it up so I’m still swaying towards K rend. 

[Conor]

I've heard nothing but negative things about K rend here in Ireland, seems in a wet climate it's green with algae in a couple years. Even my architect that has it on his house has said not to use it (his western gable wall is green). The issue seems to be the permeability and the open texture of it. The sample cards we saw at shows we're like a rough grit sandpaper that had been painted. We're looking at alternatives for our build.

[dpmiller]

^ yep more of the green or reddish-brown algae over here it seems.

[MarkyP]

I have baumit thin coat silicate,  it's very nice but this year has developed a few algae patches  i will wash and scrub it this year which should clear it, there are products to kill the algae as well. But I think any modern texture finish will attract algae. 

 

A few thoughts on renders options:

 

Sand and cement is very likely to crack, my renderer said he now refused to do it any more. Modern renders use mesh reinforcement which isn't used typically used  with sand and cement. If you do use sand and cement,  you don't have to use acrylic paint, consider the mineral paint option as well.

 

Thin coat looks much better than monocouche. Mono is the stuff which is scraped back to very textured finish and uses exposed plastic beads. I think it looks horrible. Also the deeply textured nature makes it almost impossible to clean.

 

Of the thin coat options you have three in terms of finish, acrylic, silicone and silicate. Acrylic looks plastic and is a cheap finish. Silicone can still be sheeney but less so. Silicate is my pref, it has a mineralic and matt finish. It is more expensive but coverage is vast from a tub so it's not really a big driver of the cost of the job (or shouldn't be). It has the added benefit of being over painatble with a mineral paint rather than others which would need a film based paint which wouldn't look good at all.

 

Also be wary of the texture, the larger grain size changes the look considerably. I used baumit's finest grain af 1mm, I think it was called nanopor fine and it came up really nice. I don't like the typical 2 to 3mm grain texture finishes. 

 

Make sure your contractor knows what they are doing, thin coat is a very different method to sand and cement. Ask to see some reference sites if you can. 

 

 

 

 

 

 

[Moonshine]

personally i am going to traditional sand and cement render, painted.

 

Around me there are a ridiculous amount of new builds where the monocouche render looks atrocious.

 

[Bitpipe]

The drip detail is key - where mine has gone green in winter, it is due to insufficient overhang from the roof above. It's pristine where there are proper cills etc.

 

50mm recommended for cills, 300mm for soffits.

Edited February 18, 2021 by Bitpipe

[Moonshine]

26 minutes ago, Bitpipe said:

The drip detail is key - where mine has gone green in winter, it is due to insufficient overhang from the roof above. It's pristine where there are proper cills etc.

 

i posted a video of this before as below

 

https://www.youtube.com/watch?v=GnzXw8fQhzY

 

is there a minimum overhand recommended to stop it?

 

I have got parapet walls, and think i will get issues with staining from them

Edited February 18, 2021 by Moonshine

[Mr Punter]

The through coloured stains like hell.   Sand :cement:lime, even when left unpainted, looks fine and can weather well if you don't use exposed beads.

 

Here are some garden walls we did 23 years ago.

 

[Moonshine]

15 minutes ago, Mr Punter said:

Here are some garden walls we did 23 years ago.

 

Nice, the organic nature of the staining adds to the garden.

[MarkyP]

2 hours ago, Moonshine said:

personally i am going to traditional sand and cement render, painted.

 

Around me there are a ridiculous amount of new builds where the monocouche render looks atrocious.

 

If I did mine again I would dispense with the thin coat. Baumit's base coat (star contact white) is a mesh reinforced NHL render with blended aggregates . Floated up it looked lovely and actually with a mineral paint finish would have been perfect. 

[ProDave]

17 minutes ago, MarkyP said:

If I did mine again I would dispense with the thin coat. Baumit's base coat (star contact white) is a mesh reinforced NHL render with blended aggregates . Floated up it looked lovely and actually with a mineral paint finish would have been perfect. 

Following this with interest. (I have another thread on my render problems so don't want to take this too far)

 

The Baumit base coat on it's own will absorb water, and when it freezes will crack and flake.  It cannot be used on it's own though I am open to the suggestion that it could be used with a truly waterproof paint over it?

[cwr]

Quote

Of the thin coat options you have three in terms of finish, acrylic, silicone and silicate. Acrylic looks plastic and is a cheap finish. Silicone can still be sheeney but less so. Silicate is my pref, it has a mineralic and matt finish. It is more expensive but coverage is vast from a tub so it's not really a big driver of the cost of the job (or shouldn't be). It has the added benefit of being over painatble with a mineral paint rather than others which would need a film based paint which wouldn't look good at all.

 

We're provisionally going with K-rend thin coat which I believe to be silicone, as builder reckons it is better than their monocouche. We have found many and varying opinions though, so hard to figure out what is best... 

 

Out of interest, what exactly is a 'film based paint'?

[MarkyP]

58 minutes ago, ProDave said:

Following this with interest. (I have another thread on my render problems so don't want to take this too far)

 

The Baumit base coat on it's own will absorb water, and when it freezes will crack and flake.  It cannot be used on it's own though I am open to the suggestion that it could be used with a truly waterproof paint over it?

The silicate thin coat render products are i would guess basically mineral paint with some aggregates in the mix. Lime Green do a base NHL render and told me their finish coat is a mineral paint, same tech as Keim, etc. I don't know how strong the baumit base is, it's a lime cement hybrid, probably fairly tough stuff. We left our base coat exposed all winter as it was too cold and wet to risk applying the finish thin coat. It was fine - no cracks or frost damage and got soaked and frozen repeatedly.  

[MarkyP]

29 minutes ago, cwr said:

 

We're provisionally going with K-rend thin coat which I believe to be silicone, as builder reckons it is better than their monocouche. We have found many and varying opinions though, so hard to figure out what is best... 

 

Out of interest, what exactly is a 'film based paint'?

Most exterior masonry pain is acrylic based. It coats the surface with a thin film. Think sandtex and the like. 

 

Mineral paint chemically bonds to a mineral substrate so won't ever peel off. But it needs a mineralic substrate to react with, it otherwise behaves like a regular paint over acrylic or previously painted surfaces. I suspect the same over silicone. Keim is a leading mineral paint brand, expensive but good stuff. 

[ProDave]

2 minutes ago, MarkyP said:

The silicate thin coat render products are i would guess basically mineral paint with some aggregates in the mix. Lime Green do a base NHL render and told me their finish coat is a mineral paint, same tech as Keim, etc. I don't know how strong the baumit base is, it's a lime cement hybrid, probably fairly tough stuff. We left our base coat exposed all winter as it was too cold and wet to risk applying the finish thin coat. It was fine - no cracks or frost damage and got soaked and frozen repeatedly.  

My issue seems to be our climate.  I don't want to take this off int my problems (that will evolve on my own thread) but up here, it has been average of below 0 from Christmas to last week, with -16 one night.  Extreme cold like that, coupled with a well insulated house so little heat gets out, means frost on the outside of the walls is common, and I have first hand experience of where the top coat has failed, water has got through, and the base coat, now damp, has frozen and cracked.

 

Probably not an issue in Kent?

[MarkyP]

Mine is over 120mm of graphite EPS EWI (plus existing 75mm mineral wool cavity) so the render layer doesn't get much benefit of heat from inside the house. My basecoat was left during the first "beast from the east" winter a couple of years back- days at zero to minus 5 or lower. I'm also on a very exposed elevated site, sideways rain and strong winds . I wouldnt leave base  coat indefinitely but I don't think there is much difference in thin coat vs mineral paint as base coat finish,  they are a colour finish and water proof layer, just one has some aggregates in the mix. Cracks are an issue of basecoat failure.

[cwr]

Quote

Most exterior masonry pain is acrylic based. It coats the surface with a thin film. Think sandtex and the like. 

 

Mineral paint chemically bonds to a mineral substrate so won't ever peel off. But it needs a mineralic substrate to react with, it otherwise behaves like a regular paint over acrylic or previously painted surfaces. I suspect the same over silicone. Keim is a leading mineral paint brand, expensive but good stuff. 

 

Thanks @MarkyP

[cwr]

Quote

Of the thin coat options you have three in terms of finish, acrylic, silicone and silicate

I see that you can also get 'silicone silicate' render, for example from the EWI store. Is that a mix of the two? @MarkyP (and others) what is your opinion on that? 

[ProDave]

What do people think of mixing "systems"  e,g putting a different make of top coat, e.g. krend, onto a Baumit base coat?