Render

lowdownbug

We have recently bought a house that's in need of considerable modernisation, one of the things we want to do is to change the external appearance by replacing the existing uPVC cladding on the front and back with Cedar, and renewing the existing render on the end walls. The walls are currently asbestos sheet with a very hard textured render applied, I think this was done sometime in the 60s or 70s and as it's external and doesn't present a hazard I intend to leave it in place and apply the new render over it. Over the years there has been a little movement and hairline cracks have appeared along the panel edges, so I'm looking for a smooth render that will cover the cracks and be resistant to cracking in future. I've been looking at silicone resin based renders but they seem very expensive compared to traditional renders, does anyone have any experience of these, are they worth the money, do they last, or am I better off going for cheaper traditional render and resigning myself to maintaining it every few years?

nobulljusttruth

Render is concrete. Sand and cement. Cheap to make, cheap to apply. Unfortunately concrete does not breath and any damp, moisture stays behind it, freezes in the winter, expands and then cracks. (Imagine a sheet of glass against the facade). 10 yrs later replace it.... it happens again. It also need painting on a regular basis.

Silicone renders are breathable, imagine Gortex for your walls. many old school renderers don't like it because it is 'different' to apply.
It can be more expensive as fewer applicators are out there. BUT is it coloured , does not need painting, is breathable and waterproof.
If you want a smooth finish, you can ask for a sponged finish rather that 'ashlar'. This reduces time and dust.

If the reason for the cracks is not movement of the walls, it must be moisture.

If the walls are aspestos, there may be some mileage in looking at Solid wall insulation. (if you have no cavities). there are in-roads into FREE insulation grants for external insulation at the moment.

Alternative finishes are Brick or Stone finish by Decopierre or Stonecoat operators.

Search Webber or K-Rend applicators for smooth Silicone finishes.

Hope this helps.

lowdownbug

Yes that does help thanks, you seem to be confirming the manufacturer's claims for the product which is what I wanted. I don't want to be doing tnis job again in a few years time, and if that means spending more money on a better product now that's fine as long as it really works.
The movement that has resulted in the hairline cracks is due to it being a timber frame building, clearly the timber moves slightly over time but the asbestos boards don't, so any type of render that can't accommodate that movement will also crack.
I'll check out those products you recommend and see if I can a local company than can apply them.

Furts

lowdownbug wrote: »

Yes that does help thanks, you seem to be confirming the manufacturer's claims for the product which is what I wanted. I don't want to be doing tnis job again in a few years time, and if that means spending more money on a better product now that's fine as long as it really works.
The movement that has resulted in the hairline cracks is due to it being a timber frame building, clearly the timber moves slightly over time but the asbestos boards don't, so any type of render that can't accommodate that movement will also crack.
I'll check out those products you recommend and see if I can a local company than can apply them.

Can you establish where the asbestos boards end, and establish any movement joints here? This will overcome some of the cracking.

A principle with traditional rendering was to give a roughcast, or wood float finish - this helped disguise cracking, and it could make any cracking more irregular, and easier to overcome.

A smooth steel floated finish meant cracking was far more visible, and like wise any repair. With roughcast, the coat of Sandtex, or similar, just filled and hid the cracks - much less so on a smooth finish.

If you are going for a specialist product carefully research BBA approval, and similar, and ensure you get adequate reinforcement to try to prevent cracking. You may find movement joints will be required. Bear in mind houses are not built with a timber external skin for a reason!

lowdownbug

Yes the outline of the asbestos panels is quite clear, the cracks follow the panel edges although not all have cracked, and they really are hairline cracks, you couldn't get a sheet of paper between them they're that fine. I had far more trouble on our previous house, which was also timber-framed but also timber clad and then rendered with a cement render. The cracking was quite extensive there.

Niv

'The walls are currently asbestos sheet with a very hard textured render applied, ..snip.. I intend to leave it in place and apply the new render over it.'


I assume the asbestos sheet is cement sheets. As such surely the breathability of the render is moot as you are talking about rendering over asbestos sheets which are not breathable?

lowdownbug

Correct, they are asbestos cement sheets so breathability is not really relevant, although they have been nailed to 1" battens over the original wooden shiplap cladding which was left in place so it's probably far from airtight! It's very typical of these types of riverside property which have just sort of evolved over the years from wooden sheds.

I spoke to a local approved contractor about K-Rend this morning and got a rough quote of £5300 to do my two side walls (approx 90-95m2) which seems quite a lot, but the product does come with 30 year BBA approval if applied professionally, so there's a good chance it would outlive me!