K-rend Repair

[Rosita Westhouse]

Thincoat renders, applied at a thickness of 1-3mm onto a flexible basecoat layer, usually leave a textured, slightly grained type finish. K-rend is a coloured render so if the mix isn't right the patch will stand out.

Patching k-rend may be a nightmare for some people but can be done with the right technique.

The easiest way of patching K-rend is to use the same finishing render (rendering patching compound) by rubbing it in with a piece of polystyrene.

Then, it should be given a homogenous structure with round movements by means of a EPS polystyrene piece flatly held to achieve the appearance of densely laid out aggregate grains structure.

If not properly rubbed, it will leave traces of joining and will be very visible. It is good practice to soak the edges of the applied K-rend render until it blends with the old plaster in an almost invisible way.

There are some cases where a very small crack has occurred that needs fixing. Hairline cracks tend to happen over time so if the wall itself moves or cracks, the surrounding render will also. Such cracks can not only impact the overall aesthetic of a property but also lead to water ingress, causing further issues down the line, including dampness, heat loss and mould. Small areas should be sealed as soon as they first start to show. This is because water can get through then freeze and expand, making larger cracks.

It is best if you patch larger cracks using repair filler such as all-acrylic or siliconized-acrylic sealants. Any repairs made to the cracked rendered surface should be allowed to dry for at least 30 days prior to repainting the whole of the rendered surface with exterior paint.

If your damage is really deep, none of the above methods will do the trick. In this case, you may have to cut out the piece of external wall insulation and start all over again. By doing so, you are creating a new, stable substrate onto which you can apply the thin-coat render system. While removing a piece of system might not be what you wanted to hear, putting any other materials on top of damaged render is only a temporary fix and, over time, you will see the cracks that will only continue to expand. Once a new insulation piece is in place, apply a 6mm-thick basecoat layer with embedded reinforcing fibreglass mesh followed by a thin-coat render topcoat to provide a decorative finish.

You've probably noticed that the thin coat renders are delivered as a ready-mixed product. Its chemical composition releases the resins. That's exactly what you'll use to repair small damage! It will not contain grains, only colour. It will therefore be easy to apply. All you need now is a touch up brush. Gently soak the brush in the bucket without touching the render grain. Start in the middle of the touch-up spot and work your way out to the edges. Apply the render as evenly as possible. Use light layers to evenly coat the scratch.

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Last year we bought a 1930s terrace, which is pebbledashed and painted front and back.

There are some cracks which have been sealed against water ingress (and confirmed by survey not structural) but obviously it looks pretty tatty now. It's also fairly obvious that there has been a second coat of pebbledash applied over the original coating, and some areas sound hollow so it appears to have come to the end of it's life.

We're getting our (original and rotted) windows replaced with new wood windows, and obviously this process will cause more damage to the pebbledash, so we want to know the best way to remedy this.

I've spoken to two companies - the first recommended removing the pebbledash completely, meshing over the exposed brickwork of the entire house and then using K-rend as a new coating.

The second specialises in repair, so would patch repaid the cracks, and then spray on a protective coating that would make the coverage seamless.

Neither seem the ideal option as option 1 seems to carry some risk to the brickwork and structure of the building (and I've read could invalidate insurance?) and option 2 mean that the old, failing pebbledash is still there, albeit covered up.

Just wondered if anyone else has had a similar issue, or has any knowledge over the best course of action to remedy this? Don't want to spend thousands on beautiful new windows and then make a mistake with sorting the rest of the exterior!

IME the old render will be soft, crumbly and bubbling off. I'd hack it all off.

whether you want another pebbledash in keeping with the house, or a modern, self-colour, thin-coat K-rend is up to you.

Most plasterers can apply render, but I'd suggest you look round your neighbourhood that have recently had it done to a good standard, and engage the householders in conversation. K-rend seems to have a good reputation.

it can be done from ladders, but scaffold is more usual now. This can be a good opportunity to have windows, downpipes, bargeboards etc repainted, or gutters repaired. Scaffolders wil usualy extend the rental period quite willingly as most of their effort is in erecting and removing.

If you're thinking of having cavity wall, or external wall insulation, this is the time to do it. In Switzerland I've seen external insulating slabs fixed, boarded over with some kind of cement board, and rendered overall. It does need a competent firm.

Is your house in a conservation area? If so, it would be worth checking with local planning if you have to replace with similar pebbledash to original. See link to news story for reference. www.google.com/amp/s/www.homesandproperty.co.uk/property-news/put-that-ugly-pebble-dash-back-at-once-demand-neighbours-33322.html%3famp

If it's not in a conservation area, I would consider lime rendering but definitely avoid k render and any other sort of cement render. Don't believe the guff on new versions of k render containing a small amount of lime. It still contains silicons, cement and other non-breathable materials that will cause damp problems and damage brickwork.

Can give you further info on this if you wish, but if any render is to be used, it should be lime on a period property, unless you want to cause lots of problems later on with loss of breathability.

Thanks for the replies all.

I had read something about having to install insulation if you remove pebbledash down to the brick? we don't have cavity walls.

I've been looking at all the similar houses round this area, and there is only one I can see that has smooth render, and it does stand out (and doesn't look great IMO but that's maybe because they've not painted it and it has a horrible porch).

Everyone else seems to have painted pebbledash, though some have been redone as the textures are different.

Does anyone know who could give independent advice on this? Obviously all the firms have their own product to sell, and I'm concerned now that the k-rend plasterer didn't seem to mention any kind of insulation when it seems it would be necessary

Sorry, only just realised you asked for more info.

On older properties, the principles of building were different - buildings were designed to be 'breathable' by letting moisture exit the structure through the mortar joints - lime is soft and flexible so was used for this reason.

Lime flexes and allows for small seasonal shifts in movement too.

Cement or other cement based renders/mortars on the other hand do not allow moisture to leave building structure and are rigid, preventing the building from flexing.

Modern building principles are based on preventing moisture from entering a building, rather than allowing it to escape, do using modern materials on an old building causes problems.

More info below from a well respected historic building expert who has advised RICS on new industry standards for surveys and renovation of properties.

www.heritage-house.org/damp-and-condensation/types-of-damp-what-have-i-got/damp-problems-caused-by-cement-render.html

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