FAO: Spud1,Oilman or other Stonie!

[Peter Mac]

I had mentioned this pretty far back:no replies, and can't even find it. It's the same building I'm talking about here; same sandstone. Someone with questionable intelligence smeared cement (yes, nasty grey colour portland) over the wall, in great patches, each patch being about a foot and a 1/2 square. There are heaps of these, some joined up together.

I've now started to gently remove some of these patches with just a hammer and chisel, just the ones that are hollow sounding. The stones' surfaces behind that I've now uncovered sort of dip in in the center of each one, like a "c" shape, but only around 10 -15mm in the centre at worst. This wasn't me chopping great lumps out of them, they must have been weathered when they were covered with cement.

Should I use the 1 hydraulic lime to 3 sand mix to point around these, will this be ok? Or is there a stronger mix that's better?

This work is going to take me ages as I'm not going to use power tools: the stone is rubbish enough without being trashed.

Thanks a lot;

and anyone can reply to this if they really know what their talking about. This building has been trashed already, so it needs a good repair job!

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moderator

The post you want was posted in General Diy in October (wrong forum, which is probably why no one replied) I just now moved and locked it, but for info, it is here

 

[jbonding]

what is the finish you want to acheive?

 

[oilman]

From reading Konrad's information in other posts, it seems non-hydraulic lime would be better, but there is information on his site of some additions like aluminium silicate, protien,borax and even sugar. Seems like things can get quite involved. A "stronger" mix is not a good approach, esp with soft sandstone.

 

[Peter Mac]

I don't need a fancy type finish (thankfully!), as the rest of this particular wall just has the original mix sort of pointed and then brushed around each stone so that it's smooth - it doesn't have any lines etc.

Yep - judging from how hard the cement was that was put on before, and how I managed to chip it off in big flat pieces, this hard mixture approach is not the right road to go down....I just want to make sure that the mix won't weather easily, or come off easily if someone scrapes it with something. The sandstone is pretty bad - though not bad enough for replacing.... yet!

I'll have a look at these posts of Konrads - is there a link there for his site?

Cheers Mod - I thought at first that "Building" was aimed more at construction type things than repairs.

Thanks for replying....I'll be back on tomorrow at some point

 

[KonradFischer]

Sorry for writing nearly twice the same, but I think its worth it here also:

Only a good shaped pure hydratic lime plaster will work well for repair (and new building) of masonry. There are many technical reasons, here are some of them:

1st The thermal expanding of lime mortar and stone are very even (0,5-0,8 mm/m/100K), cement mortar will expand much more (~ 1,2) than the stone. Result: Cracks of the mortar, mostly seen outside, where is more thermal difference.

2nd The drying out capacity (after Cadlergues) of lime mortar is 0,25, cement mortar 2,5. Result: The lime mortar will dry out damp ten times quicker than cement mortar. No storeing of water, much frost attack will be avoided.

3rd The binding forces by drying out of the fresh mortar is low of lime mortar and very high of cement mortar. Result: No problems of binding from lime mortar on a 'weak' surface like an old wall, jointed normally with lime mortar.

4th The cement mortars have a lot of efflorescent alkalic salt deposits in it, which can make many problems. Only pure hydratic (not hydraulic!) lime mortar has no efflorescent salts in the receipt.

5th Its not a problem by receipting lime mortar by use of 'shovel method' 1part lime - 3 parts sand. To give in modern chemicals is of doubtful use. What modern alchemy has found out is often just the opposite what a good work needs. I do prefer traditional methods in this topic too. They are proved for centuries.

6th The pore volume and size can influence the capillary and drying out behaviour of mortars very much. So the walls behind cement mortars will be more damp than behind lime mortar. But rising damp by capillary activity is not possible to a remarkable level with cement render too. The reasons of rising seeming damp you can find in the salts and other natural sources, as mentioned here: Rising damp - the experts fake

7th The first layer of joint filling mortar should be grained 0 - ~2mm, the finishing finer 0-~0,8/1mm, depending of the original mortars nearby. So you can install a capillar pump, which will hinder water to came in and improves water to come out. Remember: Capillary transports are working only from big pores to small pores, so the fine grained mortar gets small pores, the rough grained bigger ones.

If you will know more details to this topic and can understand german, try this:
Masonry - a technical Guide
In english you will find info about mortar problems here:
Problems with lime mortars and others - my RILEM-lecture in the University of Paisley 1999

The problem is, that 'modern' craftsman are not more used to work with pure hydratic lime mortars, so they will recommend other things without respect of technical behaviour. Look for an old fashioned craftsman, there are many also in the UK. Perhaps ask the National Trust or Historic lime center or my fellow Peter Cameron from Historic Scotland at Fort George, there they know the good guys (and give them my greetings).

Good luck!

Konrad

My Tip: Never use OPC and even not hydraulic lime, it hurts masonry!