Why is my limewash cracking

[KarenP]

Hi all, I wondered if anyone knows the solution to this.

We stripped our ceiling back to the original lime plaster with peelaway 1, neutralised and washed it and have now applied multiple coats of limewash (made from quicklime and water on site). In a few patches it has developed these cracks and easily flakes off the ceiling - any ideas why this is happening, and suggestions on how we can remedy this without redoing the whole ceiling?

TIA!

 

[a twig]

Probably contaminates in the surface underneath.

That looks very thick for limewash though - in my experience you usually only get failures that look like that with a thick emulsion or similar, are you adding enough water when applying?

Particularly for first coats I usually go for a consistency similar to skimmed milk.

 

[Kearn]

That doesn’t look like a crack, it’s a huge dent!

What was your mix ratio and application method? How many coats?

Limewash wants to be almost translucent when it goes on, for fresh plaster, you’re probably looking at 4-6 coats, 1 per day. It should be wet and messy, and applied quickly and firmly, without overworking it.

Have you pigmented this? As limewash would be pure white.

I’d agree, not fully neutralised in places. And too thick a limewash, which can dry too fast and doesn’t fully bond with the plaster/previous coat.

The good thing about limewash is you can just go over areas…

 

[KarenP]

Definitely a crack rather than a dent, but it’s beginning to flake away from the ceiling.

It was diluted until a milk-like consistency and applied no more frequently than once per 24 hours with a brush, but this is at least 6 coats of not more in places where we’ve already removed flaking pieces and redone it.

I wasn’t aware lime wash was at risk of being overworked, so it’s presumably either that or possibly some slightly thicker patches from the bottom of the bucket.