What is this heritage lime plaster used for?

[Jblakes]

Evening all,

Been given a good 500kg on Mike wye heritage lime plaster from a neighbour, they didn't use it in the end. It's in black bags as was delivered on bulk

I can't actually work out what's its used for, if its premixed, anygood. We have walls to plaster, after boarding but it's this actually any good?

Any ideas? Anybody used it, is so what for?

Kind regards
James

 

[a twig]

If you read the information sheet linked in that page, it answers most of your questions:

https://www.mikewye.co.uk/wp-content/uploads/2017/04/Mike-Wye-lime-putty-plasters-information-2017.pdf

Our traditional lime plasters are premixed from selected sands and mature lime putty which are then matured for several weeks. They are typically used internally.

Our Heritage Plaster mix is suitable for final coat internal plaster skimming (the ratio is 3 sand to 2 mature lime putty by volume)
Our traditional lime plasters are premixed from selected sands and mature lime putty which are then matured for several weeks.

Our Heritage Plaster mix is suitable for final coat internal plaster skimming…and is suitable for both walls and ceilings and is trowel finished….

 

[a twig]

Mike Wye has a pretty good reputation for quality of products so it will be good, but not necessarily suitable for the application you are after

 

[Lacan07]

Evening all,

Been given a good 500kg on Mike wye heritage lime plaster from a neighbour, they didn't use it in the end. It's in black bags as was delivered on bulk

I can't actually work out what's its used for, if its premixed, anygood. We have walls to plaster, after boarding but it's this actually any good?

Any ideas? Anybody used it, is so what for?

Kind regards
James

View attachment 9281

What kind of 'boarding' have you used for your walls?

 

[Jblakes]

Well it will be fibre wood board, when I stick it up. Not entirely sure if this stuff is much use for plastering on top.

 

[Zebra]

I reckon you'd need a base coat of something coarser. I did a 1-day lime plastering course at Ty Mawr, it was 8-9 years ago now so nobody shoot me down if this is slightly wrong , but as I recall you do a scratch coat which you scratch (traditionally with a cut lath, but there are tools for it that you could use) to key it, then a float coat which you flatten with a wooden float and also scratch it with a devil float (wooden float with nails protruding through) then you'd be ready for the top coat, which is what it looks like you've got.
I have plastered over woodfibre and woodwool internally, and done it myself, to no great standard but I like it.... However, I skipped the top coat, and simply sponged the float coat, because I didn't think my plastering skills were good enough, but it is quite rough, and if I had it to do again I'd probably persevere...
So I think the answer is yes you can use it, but not on its own.

 

[Jblakes]

OK cheers, does it last a while or need using up? On the lime mortar it said use within 3month. Wasnt sure if this was the same

 

[Cubist]

I have plastered over woodfibre and woodwool internally, and done it myself, to no great standard but I like it.... However, I skipped the top coat, and simply sponged the float coat, because I didn't think my plastering skills were good enough, but it is quite rough, and if I had it to do again I'd probably persevere...

Plaster is my kryptonite it has to be admitted - I could be plastering a floor and still get it in my eyes somehow - and it would appear Zebra that we share the smae skills level.

I suspect we also have in common homes where a 'rustic' plaster finish is not out of place?

OK cheers, does it last a while or need using up? On the lime mortar it said use within 3month. Wasnt sure if this was the same

So long as the tub is properly sealed and not damaged it should last much longer but will need to be thoroughly 'beaten up' before use.

 

[Jblakes]

Last question for now, anyway. Can I screw woodfibre boards straight to bare wall, it won't be flush in sections as obviously the wall isn't flat. Is this going to cause issues later on with air/moisture in the pockets?

Kind regards
James

 

[malcolm]

The aggregate size in plaster dictates the thickness. Finishing plaster has a small aggregate and it is really difficult to apply it more than about 3-5mm thick. Normally the base plaster has a thicker aggregate that allows 10mm to be thrown on at once. It's good to have half an inch of plaster. Just a skim on top of the soft insulation won't be very knock resistant.

I know the advice is to flat plaster the walls before fitting the woodfibre boards. That's what I did in my kitchen but that was mostly because my bricks were all over the place and I wanted to fit a straight work surface. Much quicker and easier to level behind the boards than try to level the finish side. I think air pockets should only be a problem if the outside of the wall is not breathable.

 

[Lacan07]

Well it will be fibre wood board, when I stick it up. Not entirely sure if this stuff is much use for plastering on top.

With wood fibre board you usually level the wall up with a lime base coat (scratch & float coat) before apply the boards. I can't think of any reason why you couldn't apply the boards to a perfectly flat masonry wall. Opinion tends to be divided as to whether its a good idea to leave air pockets behind the board. Some people apply the boards with a coat of a breathable glue type render on the back which fills any possible air pockets before apply the nails. This also helps with levelling / flattening the boards.

You then apply the finishing coat in 2 passes with mesh in-between. As Malcolm says what you have will be determined by the thickness of the aggregate. If its a fine sand then its finishing plaster. Just remember when trowelling on the lime plaster (and indeed this applies to Gypsum as well) be careful not to apply it too thin. Its a common mistake for the amateur, in the fear of it not sticking to the wall people push too hard and keep the trowel at an acute angle to the wall thereby producing the thinest application possible. The problem is your plaster will go off like a bitch if its to thin as the moisture gets sucked into the wall. Even a lime finishing coat needs some thickness to it, especially if you plan to float it.

 

[Jblakes]

OK, so seen as I've got this stuff free I might aswell use it up. Can somebody confirm if this is a good idea.

1)Mix the heritage lime plaster with sharp sand and fill in the biggest gaps between the stone (already mortared so will stick on top) to level is up, or as good as.
2) screw wood fibre boards into the wall and mesh between the joists maybe use left over mortar between gaps then stick mesh on.
3) heritage lime plaster mixed with sharp sand again, thick ish coat
4) use fine sand and heritage lime plaster for top coat.
5) done, unless I have it totally wrong.

Kind regards
James

 

[Jblakes]

Bump
Thanks James

 

[noj]

The plaster you've got is a finish mix, it wouldn't need any additional sand for the top coat.
I'd worry that it would become too weak a mix for point 3, you'd be lowering the lime ratio by adding more aggregate?
For point 1 you may be ok since it's just packing gaps under the boards rather than actually doing anything structural...

 

[Jblakes]

Thank you for that. Yes it just packing the gaps to reduce the air pockets. Can I apply two coats of this plaster on top of the woodwool boards? Or do I need something else underneath?

Kind regards
James

 

[Zebra]

Hmm, not sure whether you could make up a base coat from top coat plus more sand.... I can see the temptation to try since you have it, but adding more aggregate to something that already has the correct lime/aggregate ratio, I think you might end up with something with not enough lime in it (I think the lime/aggregate ratio may be more lime-rich in top coat, but not vastly so... but as I said, I didn't bother with top coat so can't be sure). How about if you bought a bag of hydrated (not hydraulic) lime, made it into putty, then made up your base coat by mixing together sand & putty (in the appropriate ratio) plus the top coat you have.....? No guarantees it won't fall off, but you won't have lost much trying, and then you'll have lots of putty, which is always good to have
And @Cubist yes we have in common homes in which a rustic finish is not amiss, but my skills are much better than they used to be

 

[Zebra]

Hang on @Jblakes , is it wood wool board you're using? Why did I think we were talking about wood fibre boards?... Wood wool are quite a bit stiffer and firmer than wood fibre, so you might get away with a weaker base coat on them, avoiding the tendency to damage too easily as malcolm mentioned.

 

[stuart45]

Finer aggregates need more binder to cover the particles. The finish coat is usually more lime rich, the gauge depends on the type of finish required.

 

[noj]

Another thought...
Finish plaster plus fibre (either goat hair or synthetic) could well work?
Not dissimilar to the fibrechalk/haired chalk from Anglia or the fibrelime that Ty Marw used to sell.
That way you can use a thicker float coat of the plaster without too significantly reducing the lime ratio.
Possibly...

 

[Cassie]

I’ll chip in although I’m not a plasterer, merely someone that does what needs must. I’ve used this exact stuff as top coat after patching in large areas-Mike wye is my local supplier. It’s a good quality product even in my amateur hands, easy to use once you’ve got the hang of consistency. I have a couple of tubs in my shed that are over a year old and still good so I wouldn’t worry too much about use by dates. It is def not strong enough to use as scratch coat, will crumble and lose everything on top. Presumably at some point you’ll need a top coat? Why not save it for that and don’t mess with it, get something stronger for the base coats?