Hairline cracks interior walls - widen or paint over?

[Moose]

Hi!

We’re prepping our walk in robe, three built in robes, and one linen cupboard, for the install (27/11/19) of pre-fab shelving.

The company for the shelving did the design, measure and quote, and is manufacturing. We have to remove old internal steel and wooden components, and patch and paint the walls, ceilings, and floors.

After much Workshop community support for the demolition stage, I’m now up to prepping for patching. Our house is 30 years old, double brick, and has  a layer of plaster/render (?), not plaster board.

There are many cracks inside the cavities, as well as holes from the wooden insert/nail combos that held the shelves.

I’ve done lots of searching online and everything seems to say I should widen these cracks and then fill them. There’s just so many, and some seem tiny.

Best way forward? Also, if the old paint is bumpy, should I smooth it out? I’m worried I’ll make it too smooth and the new paint won’t stick.

Thank you for any advice!

Vicki

 

[Moose]

One of the big cracks 

 

[TedBear]

Most definitely widen them first, otherwise they will just reappear a few weeks after the paint dries. It's easier than you may imagine: drag one of the sharp corners of a metal scraper along the cracks to form a shallow v shape groove, which will hold a small amount of filler. It doesn't have to be deep & wide, one quick drag will do it  An old scraper is fine to use. Putting filler over fine cracks won't work. Like painting over, the fine coating will give you the impression that you succeeded... and then crack again after a short time. Use a medium grade sand paper if you don't want too smooth a finish .I find a soft sanding block is a good option for plaster. You can wash the dust from them.

[Moose]

Thank you! On I crack then... The v is pretty much what I’ve been doing, it’s just that there are so many! Also, the cracks are so fine, and I have trouble seeing around the scraper, so I sometimes miss the crack and make another one 🤦‍♀️

[Moose]

The many many.. I’m beginning to wonder if we should have just started with new walls  

 

 

[Mathy]

Hi @Moose - I have a 1970s place which is double brick with rendered and plastered walls. I would only widen the bigger cracks like those in your photo labelled “wider cracks”- and then fill.

Often with fine cracks, what I do is sand/sugar soap walls and then apply an acrylic undercoat. Then, I fill the fine cracks that are left, sand and just re-undercoat those areas. Acrylic under coats are a form of “plastic” - quite often they will “disappear” the cracks, and because the undercoat is flexible, that’s the end of them.

One more thing, you might want to test whether the old paint is water base (acrylic) or not. Take a dark cloth and dab into methylated spirits and rub the paint. If the colour comes off, then it’s water based, if it doesn’t you’ve got an oil base paint on the walls, for which you’ll need a water base undercoat designed to stick to an oil base paint. Ask the paint people, they can point you towards a good product, cheers Deb

[ProjectPete]

I had this issue in my previous house @Moose and was advised to use this product straight over the cracks as they were (no widening), then sand and paint -  https://www.bunnings.com.au/gyprock-csr-3kg-final-finish_p0735914 

It's a thinner substance so it's easy to work into small/fine cracks. Use a 150mm flexible plastic spatula and work it across the wall.

Worked a treat.

[TedBear]

Good to know that it works under those conditions. I'll give that solution a go in future.

[Moose]

Thanks everyone - it's progressing nicely. ALthough not as rapidly as I had hoped, the deadline is Wednesday morning!!

[Jason]

Looking forward to seeing the results of your hard work @Moose.

Jason