How do I patch up cracks in external render near the damp proof course?

[Extrend]

The exterior of the house is rendered, and I generally patch up cracks with polyfilla exterior brick and render masonry and then paint over.

However, in the render about 20cm off the ground there's a straight horizontal line which I assume is the waterproofing line (damp proof course?). There's some cracking above and around this line - picture below.

I'm hesitant to patch up these cracks as I don't want to inadvertently bridge the damp proof course or ruin the waterproofing.
Does anyone have any suggestions on how to fix this cracking?

The cracks have been there for years and haven't got worse recently - I just haven't got around to fixing them. I assume they occurred when the house settled when it was built around 10-15 years ago.
 

Thanks

[EricL]

Hello @Extrend 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your rendered wall.

I recommend using the same product which is the Polyfilla 500g Exterior Brick and Render Masonry. However, to protect the line from being accidentally filled, I suggest covering it with a ScotchBlue 24mm x 55m PROsharp Blue Painter's Tape. The tape will prevent the filler from being accidentally applied to the line.

I recommend proceeding as you would with a general repair. Remove all the dirt and loose pieces of render, make sure that the wall is dry before applying the filler. Remember to fill only to the surface of the wall so that you will not have to sand anything down. I suggest removing the tape before the filler cures.

Here is a handy step-by-step guide: How to repair a rendered wall by @Nailbag 

If you have any other questions we can help with, please let us know. 

Eric

[Extrend]

Thanks EricL - appreciate the quick response

[R4addZ]

Hi @Extrend 

Filling near a damp proof course is always a tricky one, if you can't find anyting else, perhaps the community could give their opinions on the use of this product.

https://www.bunnings.com.au/gripset-betta-1kg-water-plug_p0960219?store=2404&gad_source=1&gad_campai...

I've never tried it but it sets as hard as concrete (according to the blurb) and is waterproof so can't in it's self pass moisture through it. the only question is, could the moisture travel over it's surface?

[MitchellMc]

Hi @R4addZ,

That product could work, but it’s more designed for sealing active leaks or water ingress through concrete and masonry rather than repairing render. It is a rapid-setting cement compound that’s great for stopping flowing water and forming an immediate waterproof seal, but it sets very hard and isn’t ideal for blending into existing rendered surfaces.

I do like the thinking that, as it's waterproof, it wouldn't bridge the dampcourse.

Mitchell

[R4addZ]

Hi @MitchellMc 

The inspiration behind  the thinking was from decades ago in the UK they used a silicone injected into the brickwork to create a row of waterproof bricks an then rendered over that with a mortar that had a waterproofing additive mixed in. There was a bit of a cheat in that as they always rendered over 1 metre high in the waterproof mortar as just below that, the weight of the water forces it out the bottom and so rising damp couldn't get that high if the injection DPC failed. Also some years back here I built a waterfall for a pool and used a waterproof mortar to make a reservoir for the water to be pumped into before overflowing to run down the waterfall into the pool.

I did find a powder external filler mix on the Bunnings website but couldnt find a waterproofing additive so the product I linked to was the next best option. Perhaps you know of an additive that could be used with the powder filler you sell that would make it waterproof and so have the best of both worlds?

[JacobZ]

Hi @R4addZ,

Bondall Silasec Waterproofing Cement Additive sounds pretty close to what you are describing.

It can be used in a variety of applications, with a waterproofing admix being one of them.

Jacob

[R4addZ]

Hi @JacobZ 

Well what do you know, in view of your post I was going to ask if it would be possible for you to check with the filler manufacturer if the two products were compatible. However when I went to get the link to the powder filler it turns out it is actually already waterproof!

https://www.bunnings.com.au/poly-2kg-exterior-powder-filler_p1715367

It may be worth checking with the manufacturer how waterproof and if it can be improved using the additive you linked to.