What type of sand

[michael]

Could you please remind me what sort of sand I should be using in the mix to point brickwork with lime?

To make things simple, I’m looking to buy my sand in bags from the builder’s merchant. I realise that building sand is a no no (too clumpy) but should I be using plasterers sand which the builders merchants consider to be a sharp sand or should I be using the altogether coarser concreting sand? Secondly, do you use the same type of sand for both brick pointing and brick building? And I should perhaps go on to ask what type of sand should be used for plastering/rendering with lime?

Many thanks
Mike

 

[BMcD]

Sharp sand for plastering as it has the required size range of particles to interlock and provide strength with a lime binder.
Plasterers sand or fine sharp/washed sharp as it's also known has been passed through a finer sieve and is ideal for use with cement as cement is a harder setting binder but I think lime hasn't the inherent strength when set to give a sound base when used with plasterers sand so I'd always use sharp sand for lime plastering

 

[michael]

Many thanks but what is sharp sand, concreting sand perhaps? As mentioned above, the builders merchants consider plastering sand to be sharp sand but then I suppose they are making the comparison with building sand.

 

[BMcD]

Sharp sand should have particles from around 6mm down, plastering sand or fine sharp is from around 3mm down whilst concreting sand or ballast can be from 20mm down

 

[michael]

Am I correct to assume that sharp sand should also be used for brick building and pointing with lime as well as lime plastering?

I don’t think my local builder’s merchant has this type of sand in 25kg bags. Options appear to be Builders, Plasterers and Concreting

 

[Gervase]

It's often sold as concreting sand, but can be labelled as builder's sand. It's got a coarse texture, and you can usually see a good variety of grain sizes. Don't mention to the builder's merchant that you want to plaster with it, in case they give you plastering sand, which is absolutely useless for limework. Similarly the soft sand for modern mortar - equally hopeless for limework.

 

[jason.p]

A well graded aggregate with particles 5mm or so down is best for
exterior pointing. The larger particles give tensile strength, and also look good when it's brushed back. If you're using it regularly it helps to find a local quarry that can supply exactly what you want and stick with them.

 

[Andrew Bodenham]

Following my conversion to lime a few years ago I've had a lot of success pointing and patching up base coat plaster with mixes based on sharp sand.

I've had less success replicating the very fine surface finish of the exisiting plasterwork in my (Edwardian) house. This is 'coat and a half' work with a very rough base coat onto the stonework and a final coat of almost white plaster, 2 - 3mm thick, polished to a very smooth surface.

Can the experienced among us recommend a mix for the final coat skim? Sharp sand and 'plastering sand' have been unsuccesful, as the largest grains drag through the finish or protrude from the surface. A 1:1 lime putty / building sand mix was better, but this seems to contradict all the advice I've read.

Interesting to note that quite a lot of the original plaster has suffered from surface crazing, so at least there is historical precedent for not getting it quite right.

 

[Ian Bond]

I used a fine kiln dried silica sand, mixed with the putty 2:1, and a bit richer for ceilings and patching.

(I'm mostly patching up areas, and using a rich 1:1 mix for the setting / finish coat)

And I can also confirm that some of my original plaster is crazed too. It is firmly bonded though, and I expect they routinely limewashed it all which took care of fine cracks.

I'm trying to match the existing surface finish which has been smoothed by layer upon layer of limewash, so I skim on 2 thin coats using a steel float. Probably not as it was done originally, but it seems OK.

 

[Ian Bond]

Here's some crazy 1830s plaster.

I haven't mucked around with the surface yet, other than to strip off wallpaper.

 

[michael]

Went to another builders merchant today and in addition to the 25kg bags of builders, plasterers and concreting sand (AKA aggregate), they also had 25kg bags of what they call sharp grit sand. This appears to be something between plasterers and concreting sand. No specification on grain size and the counter staff and yard staff didn’t know either. Nevertheless I’ve plugged for this one. Hope its OK for my brickwork and pointing.

 

[biffvernon]

I just dig it up in the garden. It then gets turned into various grades:

1. the big oyster shells picked out
2. through a coarse garden sieve
3. through a fine garden sieve
4. through a kitchen sieve


Uses:
1. general building work
2. plastering base coat
3. plastering top coat
4. sand/linseed oil mastic