Lime hemp plaster

[MattJones]

Evening,
Hoping someone on here might have some experience and can offer some advice.
I'm applying medium lime hemp plaster from Ty-Mawr as a base on my external walls, walls are red brick and have been stripped back and cleaned up ready to apply the plaster.
Last weekend and yesterday I did the majority of the walls with no problems just by damping down the walls and applying the hemp plaster.
Today I was hoping to do the same and get the room finished up but I couldn't get the plaster to hold to the walls, used the same technique so a bit lost on why this is.
If anyone has some tips or knows where I could have gone wrong it would help, I was just thinking I had gotten the hang of it all!
Thanks

 

[malcolm]

What technique are you using to dampen the walls? My favourite is spray the walls from the night before with a garden sprayer and do it a few times before mixing any lime until the walls become slower to suck up water but all the water is sucked up and there is no surface water.

Heating season is upon us which might make the walls dry out too fast.

 

[MattJones]

I've been using a garden sprayer but just a few hours before. I was worried about getting the walls too wet but maybe they aren't wet enough.
Currently there's no radiator in the room I'm working on so it is staying pretty cold in there.
Maybe if I just keep giving it a light spray through the week it will soak in enough to be successful, just worried about the walls I've done now but tapping on the plaster seems solid so hopefully that's all ok.

 

[malcolm]

If the lime stuck to the other walls it's probably OK. My relative humidity has gone down by 20 since the heating went on and there is a chance any heating you have elsewhere will be sucking water out of the room. It's normally too wet or too dry that causes adhesion problems. Wet is bad, dry is bad, damp is perfect.

 

[MattJones]

Yeah good point. I'll try getting a little more water into the brick then and go again next weekend.
I'm new to this so just trying to find my way through best I can. Thanks for your advice.

 

[Lacan07]

Yes, it could be a suction issue. I too use a garden sprayer but I doesn't have a proper fine mist control and I always think its a bit underpowered anyway. I think the pro's would usually use a hose connected to the mains with a spray gun on the end if they can. You can achieve a fine mist with those guns but theres much more water output too. When there's an issue with plaster not taking to the wall its usually too dry.

 

[Stevers]

For it to stick, I found that the NHL render mix for my basement chimney breast needed to be wetter than I would ever use for pointing, to the point where I got the odd shrinkage crack.

 

[noj]

The hemp holds a lot of water, it's possible to overwet the walls, it needs some suction to stick. For a pre-mix, fat lime then I found it sticks to a sucky wall/ceiling or dry wood wool but was much less willing over dg27.

A dry mix NHL version may need extended mixing or resting time for the hemp to fully hydrate?

 

[a twig]

Rather unhelpfully with the NHL hemp from Ty Mawr that I used in one of our rooms, I did exactly as you did at first and it was fine.

Assuming you started a new tub / bag when this happened, before you go sluicing down your walls don't rule out the possibility of having a badly mixed batch with not enough NHL in

 

[Kearn]

@MattJones I've been using exactly the same premixed from Ty Mawr, found it’s very stiff out of the bag and needs a thorough mix to get it usable - sometimes needing a splash of water too…

 

[MattJones]

Yeah it's been a lot more mixing than I thought it would be!

@MattJones I've been using exactly the same premixed from Ty Mawr, found it’s very stiff out of the bag and needs a thorough mix to get it usable - sometimes needing a splash of water too…

 

[MattJones]

Thanks for the replies, looks like I have a few variations to try out.
It was a new bag but they all have the same batch number on the bags I have, still I suppose this could have been an issue.
The bit I have left to finish is the chimney breast and the wall to the side of that so I have the opportunity to try one part a bit wetter and the other on the dryer side and just see which works out best.
Definitely been a tougher job than I expected going into it.

 

[Kearn]

Yeah it's been a lot more mixing than I thought it would be!

yeah, I've learned through trial and error than just a bit of knocking up isn't enough to get a usable consistency. I invested in a decent mixer attachment for the drill...not very expensive from ScrewFix so very quick solution.