Cheap lime plaster basecoat

[James34347]

I recently bought some 60mm Steico therm insulation boards from Mike Wye to fit to the internal side of the external walls of my terrace house.

The walls are currently back to the brick.

I did make the fact that they're back to brick clear when discussing which materials I needed with them, but it didn't seem to be taken into account, and with the materials I've ended up with I can only have a 3mm thick coat between the bricks and Steico boards. It seems I need an 80% contact between the boards and the wall so 3mm isn't going to be anywhere near deep enough.

On the vendors website there is a diagram that recommends a base coat of Cecil Reabilita Cal RB (although they didn't mention this to me)

STEICO Internal Wall Insulation (IWI)

The STEICO internal wall insulation (IWI) system is a highly effective solution that eliminates the moisture risk associated with IWI.

www.mikewye.co.uk

Reabilita Cal RB (Reboco) | SecilTek | Natural Hydraulic Lime Render

SecilTek Reabilita Cal RB (formerly Reboco) is a dry, pre-mixed lime render, exclusively formulated from natural hydraulic lime.

www.mikewye.co.uk

I already spend more than I was planning to on the materials I already have and I've not really got the budget to buy loads of this additional plaster.

From reading the Steico docs, as far as I can see, the only requirements for this base layer are that is flattens the wall enough to get an 80% contact between boards and wall, and that it is breathable.

Any ideas what the cheapest way to apply this flattening layer this would be?

Could I buy some washed sharp sand from my local builders merchants and mix it with quicklime?

Thanks

 

[larry]

I'd just use sharp sand mixed with NHL at maybe 3 or 4 to 1.

 

[Zebra]

I did exactly this: lime putty (made from hydrated lime available locally) with plastering sand, 3:1

 

[aockenden]

The CHEAPEST way to flatten the wall is with a thick layer of clay-rich subsoil, aka clay plaster. Clay is extremely affordable relative to lime as it requires no energy-intensive kiln firing process, you just dig it up. It’s extremely breathable (even more so than most limes). You can buy pure clay in bulk builders bags which you would then mix with sand. Or you can test your own subsoil on your own property for clay and sand content and potentially just supplement it with additional sand or clay depending on its deficiencies.

I bought 800kg of pure clay and had it delivered on-site for 175 quid. The same amount of dry-hydrate NHL would cost 3x as much (even accounting for moisture content differences.

Next cheapest is to mix your own lime mortar from sand and NHL or a fresh hydrated lime. Don’t bother with quicklime as it’s a dangerous material not to be trifled with and not worth it for the average DIYer.

 

[James34347]

Great thanks for the help. The clay idea sounds really interesting, I think if I tackle another project I'll look into digging my own clay.

Think I might go with the NHL for this. I guess I would go with an NHL 2, with a ratio of 3 to 1 lime.

When I've been researching I've found conflicting advice on the sand required, some people seem to have very stringent requirements for the sand, while others say just take what's available locally.

I guess since it's a base coat then a sharper sand would best. I believe it's important that it's washed to get rid of the fines. I've read that it needs to be 'well graded' i.e. a variety of sand grain sizes, not sure how practical it is to be too picky about that though.

Is it possible to mix it up with a handheld paddle mixer in a bucket?

Thanks

 

[Flyfisher]

When I've been researching I've found conflicting advice on the sand required, some people seem to have very stringent requirements for the sand, while others say just take what's available locally.

I guess since it's a base coat then a sharper sand would best. I believe it's important that it's washed to get rid of the fines. I've read that it needs to be 'well graded' i.e. a variety of sand grain sizes, not sure how practical it is to be too picky about that though.

I always wonder about this sort of thing. Essentially, this is a forum for traditional buildings built using traditional materials. The idea that builders of a few hundred years ago could pick and choose their type of sand and have it shipped, if necessary, hundreds of miles across the country seems somewhat unlikely to me. Notwithstanding that the Druids built Stonhenge with far flung blocks of stone, I reckon that builders of olde would have just used whatever sand was nearest.

In my part of Norfolk the soil is very sandy and was therefore probably easy to find locally. Part of our house is also built from chalk blocks and there is a large pit nearby where it was probably excavated. We also border a river, which was no doubt used a a water source and quite possibly sand and gravel in places.

As for lime, this would also have been produced fairly locally in small lime kilns. Indeed I've often thought that 'Lime Kiln Lane' must be one of the most common road names in the country. I know of two such roads within about 5 miles of us.

Having said that, purity of materials would certainly help with being able to produce consistent results and we all know that the period properties still standing after 2, 3, 4 hundred years must, by definition, have been well built while all the jerry-built ones (yes, I'm sure there were cowboy builders hundreds of years ago!) have long since fallen down and disappeared.

 

[larry]

I always wonder about this sort of thing. Essentially, this is a forum for traditional buildings built using traditional materials. The idea that builders of a few hundred years ago could pick and choose their type of sand and have it shipped, if necessary, hundreds of miles across the country seems somewhat unlikely to me. Notwithstanding that the Druids built Stonhenge with far flung blocks of stone, I reckon that builders of olde would have just used whatever sand was nearest.

In my part of Norfolk the soil is very sandy and was therefore probably easy to find locally. Part of our house is also built from chalk blocks and there is a large pit nearby where it was probably excavated. We also border a river, which was no doubt used a a water source and quite possibly sand and gravel in places.

As for lime, this would also have been produced fairly locally in small lime kilns. Indeed I've often thought that 'Lime Kiln Lane' must be one of the most common road names in the country. I know of two such roads within about 5 miles of us.

Having said that, purity of materials would certainly help with being able to produce consistent results and we all know that the period properties still standing after 2, 3, 4 hundred years must, by definition, have been well built while all the jerry-built ones (yes, I'm sure there were cowboy builders hundreds of years ago!) have long since fallen down and disappeared.

This is a wonderful point!

A sort of related take to answer the earlier question is I've used standard sharp sand from the local BM and NHL 3.5 and it's been completely fine

 

[Lacan07]

The CHEAPEST way to flatten the wall is with a thick layer of clay-rich subsoil, aka clay plaster. Clay is extremely affordable relative to lime as it requires no energy-intensive kiln firing process, you just dig it up. It’s extremely breathable (even more so than most limes). You can buy pure clay in bulk builders bags which you would then mix with sand. Or you can test your own subsoil on your own property for clay and sand content and potentially just supplement it with additional sand or clay depending on its deficiencies.

I bought 800kg of pure clay and had it delivered on-site for 175 quid. The same amount of dry-hydrate NHL would cost 3x as much (even accounting for moisture content differences.

Next cheapest is to mix your own lime mortar from sand and NHL or a fresh hydrated lime. Don’t bother with quicklime as it’s a dangerous material not to be trifled with and not worth it for the average DIYer.

My gardens full of clay lol, not sure about the effort involved in digging it up though but great option.

 

[a twig]

I always wonder about this sort of thing. Essentially, this is a forum for traditional buildings built using traditional materials. The idea that builders of a few hundred years ago could pick and choose their type of sand and have it shipped, if necessary, hundreds of miles across the country seems somewhat unlikely to me. Notwithstanding that the Druids built Stonhenge with far flung blocks of stone, I reckon that builders of olde would have just used whatever sand was nearest.

In my part of Norfolk the soil is very sandy and was therefore probably easy to find locally. Part of our house is also built from chalk blocks and there is a large pit nearby where it was probably excavated. We also border a river, which was no doubt used a a water source and quite possibly sand and gravel in places.

As for lime, this would also have been produced fairly locally in small lime kilns. Indeed I've often thought that 'Lime Kiln Lane' must be one of the most common road names in the country. I know of two such roads within about 5 miles of us.

Having said that, purity of materials would certainly help with being able to produce consistent results and we all know that the period properties still standing after 2, 3, 4 hundred years must, by definition, have been well built while all the jerry-built ones (yes, I'm sure there were cowboy builders hundreds of years ago!) have long since fallen down and disappeared.

100% - I’ve always been wary of people who get overly purist on this stuff as they often seem connected to “reassuringly expensive” heritage firms.

When we hired a stone mason to finish off renovating our bath stone ashlar, he asked us to just order sand from the local BM and then had a selection of sieves he used to get the sand sizes he needed for the very narrow joints.

That’s the only time in over a decade I’ve ever seen anyone with a justifiable reason for worrying about grades of sand.

 

[Zebra]

To answer an earlier question yes it is possible to mix plaster in a large bucket with a paddle mixer. You can even use a normal drill and a chuck for this rather than a special paddle mixer machine, but if you do this a lot it might not be very good for your drill over time - mine is kind of wobbly now...

 

[Kearn]

Can you mix in a trig - of course, as said your drill motor may burn out, I use an attachment on my SDS to get a bit more grunt. However, depending on the meter age, this may be come a bit tiring…

NHL - personally, I wouldn’t. It will set hard and brittle, and therefore the movement between wall/boards will likely break away the contact key across the board surface defeating the point somewhat - you want to minimise air gaps in the makeup, so your bricks, boards and plaster become one solid thermal mass.

Putty is the preferable option, if not a daub or clay.

 

[a twig]

Taking Kearn’s point on board but potentially disagreeing slightly - based on my experience with wood wool boards NHL2 is fine, but then wood wool tends to be stiffer so maybe there was less movement

 

[a twig]

I always used a wheelbarrow and a long handled mortar hoe - but worth mentioning that things like this exist now:

Steele Mixer Portable Cement Mixing Machine, 45kg Mixing Capacity | HANDMIX1 | Generator Pro

Lightweight alternative to conventional cement mixers, weighing just 17.69kg Cement Mixing made easy - capable of mixing a bag of concrete in around 40 seconds! 45kg Mixing Capacity Requires just one person operation to mix and transport the machine Requires no power source Compact and easy to...

generator-pro.co.uk

 

[Kearn]

Taking Kearn’s point on board but potentially disagreeing slightly - based on my experience with wood wool boards NHL2 is fine, but then wood wool tends to be stiffer so maybe there was less movement

Wood wool is stiff as you like, so NHL is deemed to be OK, I’ve just gone that route (shh!) given the time of year and necessity to enclose our bedroom asap!
Wood fibre, certainly the thinner variants, is more flexy so ‘could’ be less than ideal.

 

[Cherryburn]

Out of curiosity, does anyone know the reason for the 80% contact requirement? Just trying to avoid any thermal bridging with air being able to bypass the insulation layer?

I vaguely remember reading something about how the thermal performance of solid walls has actually been underestimated. In reality there's quite a few little air gaps between the bricks and in the mortar which add insulation overall, so you'd assume that some small air gaps might not be the worst thing in the world.

 

[Kearn]

NHL - personally, I wouldn’t. It will set hard and brittle, and therefore the movement between wall/boards will likely break away the contact key across the board surface defeating the point somewhat - you want to minimise air gaps in the makeup, so your bricks, boards and plaster become one solid thermal mass.

@Cherryburn

Air gaps won’t be insulate in this case, quite the opposite and the risk is for interstatial condensation to form within your wall. You want to create a decent, but not too thick, solid mass of material. So boards aren’t necessarily the best approach, many on brick will just go for a thick insulated lime plaster.

 

[paulc]

As for lime, this would also have been produced fairly locally in small lime kilns. Indeed I've often thought that 'Lime Kiln Lane' must be one of the most common road names in the country. I know of two such roads within about 5 miles of us.

Marlpit Lane will point to where the material for the kiln came from.
Less than a mile from where I am, there used to be brick kilns along with a small pit where the clay was dug out. The pit remains, but the kilns have long since been demolished and used as hardcore for the industrial estate that went up in its place. Large swathes of Norfolk is sand over clay on top of a limestone base. A plentiful source of traditional building materials if you are willing to dig for them.

 

[Glenn586]

The CHEAPEST way to flatten the wall is with a thick layer of clay-rich subsoil, aka clay plaster. Clay is extremely affordable relative to lime as it requires no energy-intensive kiln firing process, you just dig it up. It’s extremely breathable (even more so than most limes). You can buy pure clay in bulk builders bags which you would then mix with sand. Or you can test your own subsoil on your own property for clay and sand content and potentially just supplement it with additional sand or clay depending on its deficiencies.

I bought 800kg of pure clay and had it delivered on-site for 175 quid. The same amount of dry-hydrate NHL would cost 3x as much (even accounting for moisture content differences.

Next cheapest is to mix your own lime mortar from sand and NHL or a fresh hydrated lime. Don’t bother with quicklime as it’s a dangerous material not to be trifled with and not worth it for the average DIYer.

Thats really interesting. What ratio of clay to sand did you use? How did you mix it?

 

[mh12]

I'd just use sharp sand mixed with NHL at maybe 3 or 4 to 1.

Will this--- Blue circle hydrated lime mixed with sharp sand do instead of NHL?

Blue Circle Hydrated lime, 25kg Bag | DIY at B&Q

Blue Circle Hydralime is a hydrated lime used for increased plasticity & cohesiveness in cement, mortars & renders

www.diy.com

In terms of NHL 2 vs NHL 3 which would be the preferred option.
It appears NHL 2 is more flexible and breathabl than NH3 but less stronger and takes longer to set and strength is less compared with NHL 2.

In terms of mixing NHL with sharp sand can this achieved using the traditional method of mixing plaster-electrical plaster mixer hand held machine?

Thanks

 

[mh12]

I recently bought some 60mm Steico therm insulation boards from Mike Wye to fit to the internal side of the external walls of my terrace house.

The walls are currently back to the brick.

I did make the fact that they're back to brick clear when discussing which materials I needed with them, but it didn't seem to be taken into account, and with the materials I've ended up with I can only have a 3mm thick coat between the bricks and Steico boards. It seems I need an 80% contact between the boards and the wall so 3mm isn't going to be anywhere near deep enough.

On the vendors website there is a diagram that recommends a base coat of Cecil Reabilita Cal RB (although they didn't mention this to me)

STEICO Internal Wall Insulation (IWI)

The STEICO internal wall insulation (IWI) system is a highly effective solution that eliminates the moisture risk associated with IWI.

www.mikewye.co.uk

Reabilita Cal RB (Reboco) | SecilTek | Natural Hydraulic Lime Render

SecilTek Reabilita Cal RB (formerly Reboco) is a dry, pre-mixed lime render, exclusively formulated from natural hydraulic lime.

www.mikewye.co.uk

I already spend more than I was planning to on the materials I already have and I've not really got the budget to buy loads of this additional plaster.

From reading the Steico docs, as far as I can see, the only requirements for this base layer are that is flattens the wall enough to get an 80% contact between boards and wall, and that it is breathable.

Any ideas what the cheapest way to apply this flattening layer this would be?

Could I buy some washed sharp sand from my local builders merchants and mix it with quicklime?

Thanks

How many mm of base coat/parge coat plaster are you thinking of adding to the walls?