Top/finish coat for insulated lime plaster

[Athers1971]

Hi,

We’ve nearly finished plastering our utility room and in the end have used a NHL2 based lime plaster with perlite and coarse hemp.

We used a fine hemp in the thinner top coat, with sand as well, but when we’ve not got the finish we (her ladyship) wanted. The hemp has risen to the surface in parts and looks a little ‘too rustic’ in places.

Anyone else experience the same? What did you use to finish? Trowel? Sponge? Something else?

We may now need to apply a normal lime finish coat if this doesn’t pass quality control!

TIA.

 

[Lacan07]

Why did you use hemp in the fine coat? Did to want a rustic / floated finish?

A finishing coat should be trowelled smooth really, I always found floated finishes very difficult to get perfect. To achieve a polished finish you need a bit of water and pressure with a standard trowel (not a flex trowel).

 

[Kearn]

Sponge will pull aggregate to the surface and give you a rougher texture. Nice in some places, I’ve opted for this on our stone plinths walls internally.

Smooth, you need a stainless good quality trowel, and some patience/time to learn. Plus a flat plaster finish otherwise you’ll constantly catch edges showing the undulations in the finish.
At a finishing coat thickness, aggregate isn’t your friend, maybe washed sand dust to 2mm. Many will use chalk or similar. Certainly not hemp. You’ll just find yourself pulling the aggregate to the surface as you work it…

 

[Athers1971]

My supplier offers either the fine hemp top coat or a traditional top coat. We’ll know better next time.

 

[Lacan07]

Sponge will pull aggregate to the surface and give you a rougher texture. Nice in some places, I’ve opted for this on our stone plinths walls internally.

Smooth, you need a stainless good quality trowel, and some patience/time to learn. Plus a flat plaster finish otherwise you’ll constantly catch edges showing the undulations in the finish.
At a finishing coat thickness, aggregate isn’t your friend, maybe washed sand dust to 2mm. Many will use chalk or similar. Certainly not hemp. You’ll just find yourself pulling the aggregate to the surface as you work it…

Exactly this.

One of the problems i found with float finishes is the walls of an old house are never flat whether it be newly plastered wall from brick or an old lime wall waiting to be skimmed. And if your an 'inconsistent plasterer' in the way you apply it across the wall you may find the float correcting some of that unevenness by moving material from high spots and revealing the old plaster, or revealing some of your own inconsistency in the form of hollows. I never got the hang of it.

Far better to learn to polish and close the finishing coat. As long as the wall is properly watered and the (non hydrated) lime is just sitting their minding its own business you'll get all the time in the world to move it about, flatten it, and then come back to finally polish.

 

[Kearn]

Exactly this.

One of the problems i found with float finishes is the walls of an old house are never flat whether it be newly plastered wall from brick or an old lime wall waiting to be skimmed. And if your an 'inconsistent plasterer' in the way you apply it across the wall you may find the float correcting some of that unevenness by moving material from high spots and revealing the old plaster, or revealing some of your own inconsistency in the form of hollows. I never got the hang of it.

Far better to learn to polish and close the finishing coat. As long as the wall is properly watered and the (non hydrated) lime is just sitting their minding its own business you'll get all the time in the world to move it about, flatten it, and then come back to finally polish.

Yeah, I’ve remembered this last week that I need to get better at polishing, as we’ll never move back in at this rate otherwise with me trying to trowel a million wobbly panels … any tips?

 

[a twig]

Suitably ancient thread here and useful vid from Ty Mawr here

 

[Lacan07]

Yeah, I’ve remembered this last week that I need to get better at polishing, as we’ll never move back in at this rate otherwise with me trying to trowel a million wobbly panels … any tips?

What are using Kearn....non hydrated Lime? Personally I wouldn't use NHL, or at least not the branded stuff. The below is based on non hydrated lime purchased from the Lime Centre.

Make sure you got a decent 'standard' trowel like a Marshalltown, polishing requires a certain amount of rigidity so no flex trowels.

The stages are the same as gypsum really - apply - flatten - polish but obviously suction is key. You may find yourself flattening and polishing at the same time if suction has occurred. The only time (so far) I've ever had to wait to flatten a wall was when applying to wood fibre board which seems to have no suction whatsoever. I had to wait to trowel out the lines and then wait even longer to polish.

Basically its a dash of water and pressure to polish. Get yourself a bucket of water and a very wide brush, flick the wall your working on with water and clean your trowel (must be clean) and wet it with the brush. Apply the trowel with considerable pressure and it will close the surface at which point some fat should arise (always a good sign). Keep working the area with your trowel and keep it moist. Move the fat around. You'll find the process of polishing also has the ability to flatten or move the plaster, to certain extent, so it will remove trowel lines, some humps, and sometimes close nasty hollows (with considerable pressure). However I would deal with any ugly 'open sores' at the applying stage, tram lines or 'snots' are fine but ideally you want the wall to be free of hollows or sores before polishing.

I would sometimes apply my trowel vertically down the wall with my free hand applying extra pressure to the top of the the blade, especially in problematic ugly areas as this would always whip the fat up.

The thing about a closed or polished finish is your wall may be a bit hilly, due to inconsistent application and the fact suction may have beaten you, but it won't necessarily show even in brightest light because the surface is closed. Its just a polished, slightly uneven wall. I never got anywhere near anything looking this 'normal' with an open textured, floated finish. Discovering how to polish took my plastering skills to the next level.

 

[Kearn]

What are using Kearn....non hydrated Lime? Personally I wouldn't use NHL, or at least not the branded stuff. The below is based on non hydrated lime purchased from the Lime Centre.

Make sure you got a decent 'standard' trowel like a Marshalltown, polishing requires a certain amount of rigidity so no flex trowels.

The stages are the same as gypsum really - apply - flatten - polish but obviously suction is key. You may find yourself flattening and polishing at the same time if suction has occurred. The only time (so far) I've ever had to wait to flatten a wall was when applying to wood fibre board which seems to have no suction whatsoever. I had to wait to trowel out the lines and then wait even longer to polish.

Basically its a dash of water and pressure to polish. Get yourself a bucket of water and a very wide brush, flick the wall your working on with water and clean your trowel (must be clean) and wet it with the brush. Apply the trowel with considerable pressure and it will close the surface at which point some fat should arise (always a good sign). Keep working the area with your trowel and keep it moist. Move the fat around. You'll find the process of polishing also has the ability to flatten or move the plaster, to certain extent, so it will remove trowel lines, some humps, and sometimes close nasty hollows (with considerable pressure). However I would deal with any ugly 'open sores' at the applying stage, tram lines or 'snots' are fine but ideally you want the wall to be free of hollows or sores before polishing.

I would sometimes apply my trowel vertically down the wall with my free hand applying extra pressure to the top of the the blade, especially in problematic ugly areas as this would always whip the fat up.

The thing about a closed or polished finish is your wall may be a bit hilly, due to inconsistent application and the fact suction may have beaten you, but it won't necessarily show even in brightest light because the surface is closed. Its just a polished, slightly uneven wall. I never got anywhere near anything looking this 'normal' with an open textured, floated finish. Discovering how to polish took my plastering skills to the next level.

This is probably my terminology then… that’s precisely my process. Just that I need to improve my consistency and speed of application as the edges catch and show up the variation in thickness. On the wood wool boards, I’ve little excuse!

It’s been a while since I’ve done much, so taking a bit of time to find my rhythm again!

weapon of choice is a decent, worn in Ragni SS trowel that I seem to defer to at the moment, big enough to work well, small enough to be manageable with old panels.

Suction is good onto the wood wool, so I’m pretty much applying, levelling off and polishing before moving to the next panel. The wood fibre I’m less excited by, chatting to our plasterer he hates it as about 50% of what you trowel on comes back off! A nice sticky hemp mix will be going onto those…

For the amount I have to get through internally, I’ve opted for the Nosterfield putty pre-mix from Eden, nice to just open the lid, add a splash and knock up then carry it off. Also a tub pretty much does a panel, so it’s a good quantity. It’s good for about 8mm in one hit, so 4 before the mesh over joints and another 4 on top. Only place I’ve struggled a bit is that my mesh is only 5mm not 10 so it can be prone to dragging some aggregate up over the meshed areas.

 

[Lacan07]

This is probably my terminology then… that’s precisely my process. Just that I need to improve my consistency and speed of application as the edges catch and show up the variation in thickness. On the wood wool boards, I’ve little excuse!

It’s been a while since I’ve done much, so taking a bit of time to find my rhythm again!

weapon of choice is a decent, worn in Ragni SS trowel that I seem to defer to at the moment, big enough to work well, small enough to be manageable with old panels.

Suction is good onto the wood wool, so I’m pretty much applying, levelling off and polishing before moving to the next panel. The wood fibre I’m less excited by, chatting to our plasterer he hates it as about 50% of what you trowel on comes back off! A nice sticky hemp mix will be going onto those…

For the amount I have to get through internally, I’ve opted for the Nosterfield putty pre-mix from Eden, nice to just open the lid, add a splash and knock up then carry it off. Also a tub pretty much does a panel, so it’s a good quantity. It’s good for about 8mm in one hit, so 4 before the mesh over joints and another 4 on top. Only place I’ve struggled a bit is that my mesh is only 5mm not 10 so it can be prone to dragging some aggregate up over the meshed areas.

We all need to improve our consistency across the wall I suspect, it's the most difficult aspect for the DIYer. I always have in the back of mind the need to work efficiently when im plastering but equally i believe theres no gain to be had by rushing.

Wood fibre board isn't really that bad, I must admit it was a bit of shock for the first few minutes. The trick is to try avoid pulling down with the trowel, it won't work. But basically the key is in the use of the mesh. Prepare and cut your mesh first ready to use. Apply your first coat. The problem is you want it thick so you can't press the trowel too hard. Up and side strokes work best but basically just get it on without much consideration for consistency. Work in sections the size of your mesh so when you finish a section you immediately apply the mesh. This will have the effect of stabilising the plaster, clean your trowel and then use it press the mesh into the plaster in downwards and side strokes. Use your hawk to catch the excess plaster that will come off and put back in the bucket. They'll be plenty to come off. And suddenly your wall will be flat and plum, ready for the 2nd coat.