"High Build" coatings

[gravelld]

I've sand and cement render on my house. Some of it is shot, but most of it is still on very nicely. There are also quite a lot of small cracks.

I was going to have the render taken off and silicone render applied.

However, a builder suggested patching all the shot bits and cracks and then putting a layer of "high build" on. This is because taking the render off will be a huge job (> 220m2) especially where the render is sound and we might damage the blockwork underneath.

He reckons that when cracks form (which he seems to think will inevitably happen to all renders including silicone based ones) you don't have to grind out and re-render the crack, you just repaint this high build stuff back on and make good.

 

This is a bit of a new one to me - I'd been led to believe modern renders solve most of the problems of S&C (correctly applied of course) and so this new option is a bit... disorientating.

My other concern is: can you get smooth versions of "high build"? They look a bit overly textured to me. I want a modern look.

[Barney12]

51 minutes ago, gravelld said:

He reckons that when cracks form (which he seems to think will inevitably happen to all renders including silicone based ones) you don't have to grind out and re-render the crack, you just repaint this high build stuff back on and make good.

 

Modern renders are certainly less susceptible to cracking but (and its a big but) if the substrate it’s being applied to isnt stable then it will most definitely crack. Just take a drive around any modern housing estate and you’ll see plenty of cracked modern renders but this largely down to the fact the render is applied before the blockwork has dried out or the render hasn’t been properly decoupled from a (shrinking) timber frame. 

 

I assume by “high build” your builder is referring to the silicone based coatings that the render manufacturers sell for rectifying issues? 

 

If this is an existing building is some form of renderboard or EWI with a fresh render coat an option? It will almost certainly be cheaper than the incredibly labour intensive route of trying to remove the old render. 

[gravelld]

"High build" - this was the product specifically: https://www.sandtextrade.co.uk/product/sandtex-trade-high-build-textured-decorative-coating/

 

Quote

If this is an existing building is some form of renderboard or EWI with a fresh render coat an option?

 

Depends how much it costs. EWI would need a lot of enabling works - the gables would need extending, meter box, waste pipes, drains, one of the lean-to roofs would also have to be treated... In fact originally I wanted to do EWI but gave up because (1) the cost of the enabling works and (2) the sheer complexity of thinking about it all.

 

Fresh coat render sounds more expensive, but maybe it's an option. I didn't realise you could get a renderboard over existing render. Our verge overhangs (at the gables) are very shallow, about 40mm, not sure if that's an option. Eaves overhangs are ~200mm.

 

I've seen products like this: https://www.parex.co.uk/External_Walling_Systems/Non_Insulated_Render_Systems/Rendering_-_Lime/Base_Coats_-_Lime/Parinter.aspx which I believe have a mesh in them, then top with the covering of your choice. But rendering seems to bring extra cost, e.g. scaffolding (the "high build" is referred to as "painting" by the builder who seems to think a scaffold tower at most is required).

[Barney12]

59 minutes ago, gravelld said:

Fresh coat render sounds more expensive, but maybe it's an option. I didn't realise you could get a renderboard over existing render. Our verge overhangs (at the gables) are very shallow, about 40mm, not sure if that's an option. Eaves overhangs are ~200mm.

 

I’ve seen it done a few times but always battened first which might cause you an issue with your gables.

 

[Mr Punter]

I have seen this applied. It looks a bit like Artex broken leather pattern but has not cracked or needed painting 6 years down the line.

[gravelld]

Yeah, that's the problem - most of the finishes seem a bit too rough for me. There is a smoother option with a flat trowel I think but even that looks a bit rough.

 

It's an intriguing (new) idea (to me) to patch and then paint with something that has some elasticity and is easy to maintain. This means I could save up for EWI down the line.

[gravelld]

I did a bit more research and it looks like there's a category of paints called "elastomeric" paints which are supposed to be flexible.

Bedec Extra Flex Masonry is one product I've seen mentioned.

 

I wonder if it would be best to patch then paint with one of these products... this might retain the existing texture.

[Big Jimbo]

I have used the elastomeric paints in the past. if you let it go off a bit on the brush or the roller it goes a bit rubbery. I think there is defo some stretchability to it, so small hairline cracks would not show through. I can't remember if it has silicon or something in it, but it repells water, and is kind of self cleaning with the rain. It still looked good after about 8 years.

[gravelld]

Good to hear, thanks. Sounds like I have a new plan forming... any specific product reccos gratefully received.

[Adsibob]

On 27/02/2019 at 11:25, gravelld said:

Good to hear, thanks. Sounds like I have a new plan forming... any specific product reccos gratefully received.

@gravelld what did you end up applying to your house?  I'm facing similar issue now: I have a 1930s semi covered in pebbledash that has been painted white. I'm not keen on the rough finish of the pebbledash and it has lots of cracks and some bits are causing damp patches on the inside of the house, so the whole thing needs something doing to it. Surveyor looked at it today and identified various sources of damp and said the ideal solution, if affordable, would be to remove it completely and then apply a new product, but he hasn't made any recommendations yet. I'm still to find out from the builder how much it's going to cost to remove the existing. If too expensive, the surveyor did say I could apply a mesh and then render over that, but he said that wouldn't be as good as removing the old stuff. But my situation might be different to yours as you don't sounds like you had damp patches.

[gravelld]

Something called SecoFLEX. As I didn't use anything else I can't really compare it to anything else, but in general it's stood in good nick for the past year and a half. No cracking yet.

 

The contractors removed the bad bits, replastered and then recoated.

 

If you're going to the trouble of scaffolding and removing the existing, maybe consider EWI with a silicone render.