Gate Pillars

[Onoff]

1 hour ago, pocster said:

The first question is, why are you trying to make a lime mortar when you seem to have used a cement mortar for the rest of the wall?

 

As I understand it a mix containing ordinary cement mix can shrink away from the impermeable flints causing them to go "loose". Water gets into these pockets, freezes and blows the wall.

 

Others here have said the hydrated lime is OK to use I think.

 

Washing up liquid should never, ever be used as an admix.

[Onoff]

Just playing (again) with laying out the flints I have. Basically got 4 boards and marked the areas to fill. Vague recollection of someone saying aim for a finger width's of mortar between the flints.

I do have a set of copper boppers I bought but struggle to shape the flints tbh.

I think, in all honesty I'd prefer the mortar for the flints to match the 4:1 I used for the bricks. Is there any way to make it (the mortar) "flexible"?

Adding lime I believe acts as a plasticiser, is that the same thing?

 

 

 

Tbh I'm not at all happy with the strength of my sample mixes containing just lime & sand. Reading the new lime bag and I'm not sure how I missed where it says it's no good for mortar without cement in the mix! Wondering therefore if a mix containing cement and lime will give strength but also flexibility so the mix doesn't shrink away from the flints?

 

 

 

 

[Stewpot]

Outside my experience, but I doubt you can easily make an OPC mortar flexible. Plasticisers are about workability during use, not flexibility of the end result.

 

I understand your concerns about the mortar shrinking away from the flints, but it looks like you have pretty small areas of flint infill - I wonder if you would get away with just continuing with an OPC mix. The thing is, it's pretty unconventional to mix OPC mortar with lime mortar - they generally don't work well together. Usually, someone who doesn't understand the difference will, for example, repoint a lime mortar with OPC, with disastrous results later. In your case, you are, in a way, doing the opposite, by covering OPC with lime. Maybe that'll work fine.

 

Either way, I think it's a bit of a leap in the dark.

 

If you do use a lime mix, you may only be able to get a close colour match by using mortar pigments, and experimenting.

 

If you choose to use a lime mortar, it would probably be easiest for you to get hold of some NHL3.5 (Natural Hydraulic Lime, which has a strength rating of 3.5 - ie, moderatly hydraulic). There are several online outlets if your local BM won't get it. Mix it in much the same way you would OPC - no need to make a putty out of it first. I once repointed a stone wall this way, and found it easiest to use my gloved fingers to get a neat finish between the uneven stones, rather than a proper pointing tool. But keep the stone faces clean. Afterwards, keep the mortar damp - plant sprayer every day, and protect from direct sun - for a couple of weeks or so to aid carbonation and full curing.

 

Also be aware that, whist quicklime is the most reactive form of lime, all types of lime are caustic - PPP is highly recommended. If you are using powder, a mask is a good idea, and in any case, gloves a must, and eye protection sensible.

[Onoff]

1 hour ago, Stewpot said:

I understand your concerns about the mortar shrinking away from the flints, but it looks like you have pretty small areas of flint infill - I wonder if you would get away with just continuing with an OPC mix.

 

I'm coming round to the idea, I can keep the new bag of lime for getting for getting rid of the body... ?

 

The one thing I will say about these sand/lime mixes only is they seem to be getting harder by the day. Is it something to do with them absorbing atmospheric CO2 and eventually reverting to limestone?

 

Video of the 2 sharp / 1 lime sample:

 

Then the 1.5 sharp / 0.5 soft / 1 lime:

 

As I understand the method of laying flints I need to place a board against the wall then hold the flints tight against the board and infill from behind. Quite how that'll turn out when I remove the board I don't know as I'm guessing an opc mortar might dry quicker. Maybe there's an optimum for removing the board with slump and still being able to tidy round the flints.

 

Yet again, soft sand or sharp if I go with opc and no lime?

 

Aiming to start tomorrow whatever and hope!

 

 

[Stewpot]

1 hour ago, Onoff said:

The one thing I will say about these sand/lime mixes only is they seem to be getting harder by the day. Is it something to do with them absorbing atmospheric CO2 and eventually reverting to limestone?

 

Lime is a fascinating subject, and I'm only in the foothills of the knowledge base.

 

The lime cycle is a thing of beauty (to a simpleton like me). You start off with limestone (calcium carbonate). Then you heat it up, which causes carbon dioxide to be released, leaving quicklime. Slaking this with water results in calcium hydroxide and a lot of heat (it can be a violent reaction). But then, slowly, it begins to re-absorb carbon dioxide so the material turns back into calcium carbonate.

 

In other words, you dig a type of rock out of the ground, process it into a workable, sticky substance that you can glue bricks together with, and then, magically, it turns back into the rock that you started off with. And as it re-absorbs the carbon dioxide that was given off when you burnt it, it doesn't do nearly so much damage to the greenhouse that OPC does.

 

But that means it cures over a fairly long time. I've heard that in very thick walls (I guess we're talking castles with 6 feet thick walls), the innermost mortar never gets enough exposure to air and moisture to fully cure. Keeping the mortar moist for a while is an essential part of enabling it to fully carbonate, so you will see walls with hessian sacking over them, keeping them damp.

 

Without wishing to sound too much like a nerd (but I really do find it interesting), hydraulic lime has impurities in it which gives it the quality of a fast initial set in response to mixing it with water, hence its name. In that respect it behaves somewhat like OPC, but it will then slowly continue to cure by absorbing CO2, as above.

 

1 hour ago, Onoff said:

Yet again, soft sand or sharp if I go with opc and no lime?

 

If you're going with OPC, surely use the same mix that you used for building the wall.

 

Edited August 29, 2021 by Stewpot
Misreading the question

[Onoff]

13 minutes ago, Stewpot said:

If you're going with OPC, surely use the same mix that you used for building the wall.

 

Dunno, back to the potential shrinkage/frost pocket worry. So many options.

 

Got myself in a bit of a pickle, a...

 

 

...you might say!

 

 

[SteamyTea]

27 minutes ago, Onoff said:

...

 

What I need to go with tonight's supper by the sea.

 

[Onoff]

I quite like the complexity of this mix suggested on another forum:

 

"When doing flint work I use 4 sharp sand, 2 soft washed(building sand), 1 lime and 1 white cement".

[Pocster]

12 hours ago, SteamyTea said:

What I need to go with tonight's supper by the sea.

 

Stop drinking that coke shite 

[SteamyTea]

3 minutes ago, pocster said:

Stop drinking that coke shite 

Coke is the second bet drink there is, end of.

[joe90]

@Onoff have a read of this…..

https://www.buildingconservation.com/articles/flint/flint.htm

found this…..

• sheltered exposure lime putty 1 : well graded sharp sand 1.5 : porous limestone 1.5 : brick pozzolan 1
• moderate exposure natural hydraulic lime (NHL2) 1 : well graded sharp sand 1.5 : porous limestone 1 
• severe exposure natural hydraulic lime (NHL3.5) 1 : well graded sharp sand 2.

[Onoff]

1 hour ago, joe90 said:

@Onoff have a read of this…..

https://www.buildingconservation.com/articles/flint/flint.htm

found this…..

• sheltered exposure lime putty 1 : well graded sharp sand 1.5 : porous limestone 1.5 : brick pozzolan 1
• moderate exposure natural hydraulic lime (NHL2) 1 : well graded sharp sand 1.5 : porous limestone 1 
• severe exposure natural hydraulic lime (NHL3.5) 1 : well graded sharp sand 2.

 

I have seen that before thanks. It would mean changing to natural hydraulic lime and binning the hydrated I have here. I see Lawsons builders merchants near me do it. Certainly not cheap down this way!

 

https://www.lawsons.co.uk/search?q=Hydraulic lime

 

I'm shortly going to knock up a test of:

 

4 sharp

2 soft (orange builders)

1 lime (hydrated)

1 opc

 

...and see what that looks like.

 

I am concerned I won't be able to get the demarcation between brickwork and flint panels neat hence back to thinking about a trim.

[Onoff]

Here's a mad thought...

 

Time and techniques have moved ever onward. The issue with using normal cement mortar is one of shrinkage around the flints, frost action and cracking. Could I perhaps lay them in the same 4:1 mortar mix I used for the pillars then when cured just spray them with a water seal like Thompsons or Permagard?

[Stewpot]

1 hour ago, Onoff said:

... when cured just spray them with a water seal like Thompsons or Permagard?

 

Sheeesh... Don't say it so loudly - this is a public forum, you know.

 

But I was thinking the same.

 

Also, you could try making the mix very dry - think the sort of consistency you make sandcastles out of. This may help prevent shrinkage a little, and if you work upwards, making a bed, setting the flints, packing around, etc. you might not suffer any slump.

[Stewpot]

5 hours ago, joe90 said:

@Onoff have a read of this…..

https://www.buildingconservation.com/articles/flint/flint.htm

found this…..

• sheltered exposure lime putty 1 : well graded sharp sand 1.5 : porous limestone 1.5 : brick pozzolan 1
• moderate exposure natural hydraulic lime (NHL2) 1 : well graded sharp sand 1.5 : porous limestone 1 
• severe exposure natural hydraulic lime (NHL3.5) 1 : well graded sharp sand 2.

 

I wonder what they mean by 'porous limestone'? Presumably ground down to a fairly fine aggregate, but do they mean limestone straight out of the ground, that hasn't be processed in any way, or do they mean some sort of reactive lime to complement the lime binder?

[joe90]

1 hour ago, Stewpot said:

 

I wonder what they mean by 'porous limestone'? Presumably ground down to a fairly fine aggregate, but do they mean limestone straight out of the ground, that hasn't be processed in any way, or do they mean some sort of reactive lime to complement the lime binder?

I did wonder that???, but then again trying to mix a lump of limestone would be difficult?‍♂️(Limestone is porous).

[Onoff]

@Stewpot as I understand it, with the hydrated lime I have here then that's calcium hydroxide. It will, over time turn back into calcium carbonate aka limestone?

[Stewpot]

1 hour ago, Onoff said:

@Stewpot as I understand it, with the hydrated lime I have here then that's calcium hydroxide. It will, over time turn back into calcium carbonate aka limestone?

 

If it's able to absorb carbon dioxide, then yes, I think that must be right (CaH₂O₂ + CO₂ = CaCO₃ + H₂O ie. calcium carbonate + water).

 

As I say, I've never used hydrated lime as the binder in lime mortar. People say you can use it, but it is coarser and less workable, and gives less satisfactory results. I don't know why this is, but I wonder a couple of things:- Is hydrated lime able to absorb CO₂ as readily, and maybe the particle of the powder is different, and less able to mix and bind together as well. The advice is always to make a putty out of it first, but notably, whereas non-hydraulic lime needs soaking under water for months, for hydrated lime they say only a couple of days - there is no benefit leaving it longer. So there must be some difference there.

 

But really, I think the areas you are doing are quite small, and even using an OPC mix, the risks may be pretty insignificant. If it was a large, load bearing wall, that'd be different. And also, I think you'll struggle to match colours if you change the materials.

[Onoff]

Still undecided as I am on mix I knocked up a quick frame of pallet wood, divided into 4 to represent the 4 flint panels. Dumped some sharp sand in each. Apparently I get to choose the stones for one then SWMBO and the kids one each.

 

This is my attempt (the rectangular gap at the end nearest the camera is where the intercom sits). I might change the couple of whiter stones for blacker ones.

 

 

I've read that "fist size" are ideal but without knapping them this is the best I can do. If I start knapping I'll likely end up with just loads of broken flints!

 

Playing with the second panel:

 

 

Some don't have a tail / much depth so I'll be relying on the suction of whatever mortar then CT1 when bits fall out!

[Pocster]

What we doing again ??

[Onoff]

35 minutes ago, pocster said:

What we doing again ??

 

Bungaroosh mate.

 

Bet you've seen more than you're fair share, nose to the wall in Brighton etc...

 

?

[Pocster]

41 minutes ago, Onoff said:

Bungaroosh mate.

Had to check that . Was disappointed as I thought it was a curry 

[Onoff]

I've decided on my mix. Was waiting for SWMBO and the kids to lay out their panels. SWMBO had a go and imo it looks alright (panel No 4) but I don't think it'll work as there's little depth to the stones she's chosen. Thinking these shallow stones will maybe fall out over time?

 

 

 

[Onoff]

As alluded to above SWMBO has chosen some very pretty but unfortunately shallow flints that have very little tail.

 

If I were to clean each flint (dishwasher?) then "glue" a small offcut of stainless mesh to the back would that work?

[Gus Potter]

On 20/09/2021 at 08:23, Onoff said:

I've decided on my mix. Was waiting for SWMBO and the kids to lay out their panels. SWMBO had a go and imo it looks alright (panel No 4) but I don't think it'll work as there's little depth to the stones she's chosen. Thinking these shallow stones will maybe fall out over time?

 

 

 

Onoff..

 

You are a star! .. what lovely hands. Are they yours? and the flints look great by the way.

 

My view is that cement is not an option. All cements shrink.. flints have a very smooth impermeable surface and you won't get a flexible bond if you use a mix with any cement content.

 

Plenty info about lime mortars from other poster already.

 

One great thing is that if you use non hydraulic lime you can do a foot or so every few days.. just have fun! Just put a cover over it to keep the rain off. You may build say a foot every few days, but if it's not looking right you can take it off, clean the flints and have another go. Harder to do if using a cement based mortar.

 

I real life you just need to get on with it, stand back and see how you go! even if you have a template once you get a foot or so up it will all go to pot.