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How to fix internal render wall spiderweb cracks?

AusDIY

Hi folks, 2 issues I need help with or at least some advice.

House is a double brick with internal walls rendered. After removing the cornice, I found spider web cracks on the top section around 75cm long with multiple splits. It is loose. I want to chip all the cracked loose bits out and 're cement' the top part. What would be the best product to use? I saw the Dunlop 5kg Ardit Rapidset Repair Mortar, is that any good or is that the wrong product for this fix?

https://www.bunnings.com.au/dunlop-5kg-ardit-rapidset-repair-mortar_p0760262

There are cheaper products I saw like Australian Builders 20kg Quick Set Mortar Sand and Cement Mix, Australian Builders 20kg Sand And Cement Mix Bag but not too sure if it is the right product. Then there are 20 other ones, so confusing.

2. There is another crack on the adjacent wall, see below. What would be the best product to fill that in with that will cure fast and will last. I was looking at Selleys 440g Off White No More Gaps Bricks And Mortar Gap Filler.

https://www.bunnings.com.au/selleys-440g-off-white-no-more-gaps-bricks-and-mortar-gap-filler_p0266923

Whole room will be repainted, ceiling and walls.

Any help with the right products to use will be very appreciated. Thanks in advance.

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MitchellMc

Hi @AusDIY,

For the loose and cracked section at the top of the wall, I think the Dunlop Ardit Rapidset Repair Mortar would be the more appropriate choice. I'd remove all the loose and drummy material until you reach a solid, well-bonded surface, clean away the dust and debris, and then rebuild the area with the repair mortar. Once cured, you can use a suitable finishing compound if required to achieve a smooth surface before painting.

However, the amount of cracking you're seeing is reasonably substantial, particularly as it extends along the wall and appears to have caused sections of the render to separate. Before simply repairing it, I'd investigate whether the cracks are limited to the render or whether the brickwork behind it has also cracked or moved. If the masonry itself is cracking, it would be worth having the area assessed to rule out ongoing movement or a foundation-related issue. Otherwise, there's a good chance your new repair could simply crack again.

I'd take the same approach with the crack on the adjoining wall. Open it up enough to determine whether it's just the render that's affected. If it's a relatively minor, stable crack, a flexible masonry gap filler could be suitable before repainting. If the crack continues through into the brickwork, I'd investigate the cause rather than filling over it.

Let me tag @Nailbag to see if he has any thoughts.

Please let me know if you have any questions.

Mitchell

AusDIY

Thanks mate. The outside brick is not cracked but it is a double brick so the internal bricks could be splitting. No signs of it though, seems render only. Once I chop out the loose spider web cracks, I will be able to peek behind at the brick to confirm. The house was built in the 80's so any foundational work or structural rework would probably be so cost prohibitive that it would 'write off' the house.

MitchellMc

That sounds encouraging @AusDIY. If there are no corresponding cracks visible in the external brickwork, then hopefully you're dealing with deterioration or movement of the internal render rather than a more significant structural issue.

As you've mentioned, removing the loose and drummy sections should give you a much better opportunity to inspect the internal brickwork. If the bricks and mortar joints behind the damaged render appear sound and there are no significant cracks running through them, I'd be comfortable proceeding with the render repair.

I wouldn't be too concerned about assuming the worst at this stage. Some cracking and separation of an older render layer isn't necessarily indicative of foundation problems. It's simply worth checking the substrate while you have the opportunity.

Mitchell

AusDIY

Good news. The brick is not cracked. It was just the top render. Here are some updated photos after removing the cracked pieces. As I was about to buy the Dunlop 5kg Ardit Rapidset Repair Mortar, I saw another product which is a lot cheaper, Davco 20kg Off White Render, is this suitable vs the Dunlop Ardit Repair Mortar?

MitchellMc

That's good news @AusDIY .

Yes, given you've now removed a substantial amount of the existing render, I'd go with the Davco 20kg Off White Render. It's designed for rendering directly over masonry such as brickwork and can be applied from around 4–10mm thick.

The Dunlop Ardit Rapidset Repair Mortar I recommended earlier is more suited to smaller localised repairs, cracks and holes. Now that you've exposed a larger area, a conventional render makes more sense and will certainly be more economical.

Just make sure you've removed any remaining loose or drummy render and thoroughly cleaned away the dust before applying the new render.

Mitchell

AusDIY

Thanks bud. Used the Davco Cement Render ($14). Came out ok. Not pretty but not bad for first time renderer. Better than having spiderweb render cracks. I also used Bondcrete as a bond coat (1:4 Bondcrete:Water) by brushing onto the brick and waiting for 20 mins to get tacky before applying the render. I then also used Bondcrete for the render mix (1:10 Bondcrete:Water). Now the damn 7 day wait for initial cure and remembering to lightly water mist twice a day. New appreciation for people that render as a job, what a pain. More render fell on the floor as I was applying it (unskilled technique) than ended up on the wall haha. Luckily I got the 20kg bag.

MitchellMc

Many thanks for the update @AusDIY. It looks like you've done a fine job.

Once fully cured, you can take a https://www.bunnings.com.au/trojan-concrete-rubbing-stone_p0423009 and knock back the high spots, smoothing the render off. Remember to wear personal protective equipment, especially a face mask and safety glasses.

Mitchell