repointing brickwork

Page 2 of 2  
     snipped-for-privacy@meeow.co.uk (N. Thornton) writes:

It sure isn't simple, and neither is it the case that it's completely understood. I used to have a neighbour who taught brickwork, and his comment was that we're discovering what we don't know about cement based mortars faster than we're working how to use them properly. We know (or at least used to know) much more about lime based mortars, since we've been using them at least 200 times longer.
However, I recall reading somewhere a few years ago (possibly in this newsgroup) that the BRE had experimented with various cement/lime mixtures, and the 1:1 was quite good. Any less lime and the mortar loses all the movement and self-repair qualities of lime, so you'd be back to the problems you get repointing a lime mortar house with cement. I think there were problems with mixtures containing more lime too (until you get to pure lime of course), but I can't recall what that was.

I've not come across it in mortar, but it's certainly used in scratch coat lime plaster. This stops it cracking as the lime mortar walls move around. The dot-n-dab plasterboard fixing is loaded with plastic fibres too to give it tensile strength. The tutor on my plastering course demonstrated how effective that is by hanging his weight on a piece of board fixed up with the stuff, and it showed no sign of giving way.

Silicone bath sealant? ;-)
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Andrew Gabriel wrote in message ...

will wash away with the first rainfall. If the mortar *and* the pointing were the same, maybe....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Long before portland cement, lime mortar brickwork usually had some cement in the exterior pointing (exterior pointing was not done as the bricks were layed, but later). Most of mine has lasted 100 years without any trouble, and where it hasn't, it's due to some unreasonable influence happening subsequently like bridging the damp poof course or failing to repair leaking gutter downpipes (not me -- previous owners;-). There were also a couple of small places where someone had repointed wrongly (in one of them, using pure cement and no sand -- a bugger to get out).
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Andrew Gabriel wrote in message ...

non-hydraulic lime alone has ever been successful externally.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My house is rendered in hydraulic lime and sand, which gives it a wonderful mushroom colour. We were going to limewash it, but liked the finish so much we decided to leave it alone.
John
--
John Rouse

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I shall stick my head above the parapet and call myself an expert ...
There is already mortar between the bricks, so the pointing is not there to stick the bricks together. It is there as a sacrificial layer.
Rain (water, salt, acid ...) is driven into the brick surface and then when the weather improves, leaves by the easiest escape route. If the pointing is weaker than the brick, then the easier route is through the pointing. Over the (many) years this causes the pointing to wear away and eventually the bricks will need repointing. This is a much better situation to be in than if the pointing is stronger than the bricks because then the surface of the brick wears away leaving the soft core exposed which wears away quickly. OUCH!
Consider three situations:
Old soft bricks, pointed with lime mortar. Lime mortar is weak, even with a pozzolan added, so the bricks will be OK.
Modern, hard bricks pointed with cement. So long as the cement mix is fairly weak this should be OK too. I'm not a cement expert so I assume that others know better than me and that a that a 1cement:1lime:6aggregate mix is OK. (The lime is just there as a plasticiser and a red herring)
Old soft bricks pointed with cement. The cement is stronger than the bricks so producing the effect which I can see outside the window as I sit here. An old red brick wall has a grid of cement pointing but the bricks in between the pointing have worn back by about 10mm since it was done. This is a problem which has shown up particularly in the last 50 years, partly because late 20thC builders have no experience of lime mortar, but also because Portland cement today is MUCH stronger than the cement of 100 years ago.
The thing to understand is that a weak mortar is not a poor mortar. The mortar must be weaker than the brick.
I shall create another message about pozzolans which seem to be causing a lot of confusion. -- ~~ Anna Kettle, Suffolk, England |""""| ~ Lime plasterwork, plaster conservation / ^^ \ // Freehand modelling and pargeting |____| www.kettlenet.co.uk 07976 649862
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@meeow.co.uk (N. Thornton) wrote in message

Wickes (in their Good Ideas Leaflet no. 12 at http://www.wickes.co.uk/scat/goodideas ) advocate the addition of plasticiser to standard mortar to get the benefit of lime mortar; ie making it not too rigid or hard. Anyone had experience of this or care to comment?
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
     snipped-for-privacy@hotmail.com (Lobster) writes:

I always use it when I'm not using lime. However, not everyone is convinced it's a good idea.
I always use waterproofer too, with either lime or plasticiser. (Sometimes I use all 3 if I only have a combined plasticiser/waterproofer and want to use cement/lime mortar mix.)
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"N. Thornton" wrote:

No it has not. See below.

Erm, NT, I think you've become confused. This is doing people a big dis-service. There is nothing wrong with 1:1:6. For a brief and easy-to-understand look at the subject, please see:
http://www.buildingconservation.com/articles/cement/cement.htm http://www.bricksandbrass.co.uk/diymats/lime/lime.htm
Please note carefully that above I said "approach 1:2:9".
A LOT of mis-information has recently been spouted by those with vested interests in the lime production/use fields. 1:1:6 has been around for a long time - about 150 years.
J.B.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK so if I understand correctly, according to this, 1:1:6 is fine, but some cement lime mixes arent. I know little about lime mortars, I read some articles and paper a year or so ago, some from English Heritage, and the concensus of them all was that lime cement mixes should be avoided. I guess, as the article you refer to says, there are differences of opinion. I expect I'll be using 1:1:6 then, thanks for the info.
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I always use 3 to 1 mix for pointing, any specific reason you have to use lime? Are you matching in to some old pointing? Tel
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"N. Thornton" wrote:

What is your source of information? It's fine to clean external brickwork by non-destructive means. Things like sandblasting or scabbling are right out though! You don't really want a build-up of moss etc. on your house!

See other post. I'm not trying to be nasty!

Cement is a pozzolan, too!

I had a job on Wed/Thu fixing skirting/picture rail, some to a party wall. On the party wall I didn't use "hammer", just an ordinary drill with a newly-sharpened masonry bit. No problem at all (LBC commons). Not too noisy, either.

Do you mean rejects, or regrades? Rejects are junk, cracked or mis- shaped, used for hardcore etc. Regrades are bricks that are fine except for slight damage and colour problems. You wouldn't want to use them for facing. There are/were many, many types, textures and colours of bricks. There is likely to be a "brick museum" or a "brick library" at a BMs near you - for fun, 'phone up a few to see if anyone knows where (or say approx. where you are & I'll see what I can do). Obvious variations are from Staffordshire blues and similar which are as hard as hell, to Baxi decorative bricks used in fireplaces, which aren't as hard as your thumbnail.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Am I allowed to have my house sandblasted (to be followed up by repointing and coating with waterproofer)? It's worrying me; but how else do I remove all the old bits of crud and cement left behind when the render was hacked off, to restore the facade both aesthetically and functionally?
Thanks David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I cant remember Im afraid. Youre saying scrubbing old bricks up wont make them go green? Thinking about it it makes sense. I expect only if they have water sitting or splashing on them theyre likely to green.

I've got that. What's the best action?

Rejects. In Victorian times as many as 50% of bricks made on site were rejects: broken, cracked, funny shaped, undercooked and too soft, etc. Bricks were generally made by itinerant gangs who came to the site, dug up the clay and burnt the bricks on site. Later pressed bricks took over. Aesthetically the hand made bricks are far nicer, but the reject rate was high, and the junk was normally used for the inner skin of the wall.
I just wondered if you might be going into undercooked bricks there.

Theres a good site online, cw lots of piccies, I lost the address though.
Regards, NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Christian McArdle wrote:

A problem with the fixings and corrosion?
J.B. --
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Not that I can tell. Most of the slates are still present, they've just rotted away at the edges. They are 100 years old, though.
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If you want to be picky, then the word pozzolan only applies to volcanicash from Pozzolano in Italy. I shall use the word pozzolan in a much more general way and the pozzolan which is normally used today in UK is brick dust.
Pozzolans are impurities which are added to a pure lime mortar to give it some cementitious properties; to make it harder and more impermeable to water. When lime putty mortar is used outdoors, then pozzolans are always added to give it some extra weather resistance.
Hydraulic lime mortar contains natural pozzolans, so is fine for using outdoors without any more additives.
Hydrated lime should be put in a tub of water for a couple of days when lo and behold it becomes lime putty. Pozzolans can then be added for external work.
Once pozzolans have been added to lime putty mortar, it will start to set and so normally is used the same day.
To say that hydraulic lime (or lime putty mortar + pozzolan) have cementitious properties is misleading because todays cement is MUCH stronger than either. I don't have the figures to hand but my dodgy memory thinks that todays cement is about 10 times as strong as cements of 150 years ago and 20 times as strong as hydraulic lime mortar. Castle Cement have done lots of research on this.
Until a few years ago, a little Portland cement was often added to lime mortar to act as a pozzolan but there were too many mortar failures so English Heritage commissioned some research.
The results of the research were published as "The Smeaton Report" and in summary the report says that that cement+lime mixes will succeed if there is enough cement in the mix to get a _cement_ set. The lime is there just to provide plasticity.
What does NOT work is a mix where 'just a little' cement is used as a pozzolan because the cement clogs up the pores of the lime so the air and water which are required for a _lime_ set can't get into the matrix. Mortar failure is likely because there is a poor lime set and not enough cement for a cement set.
-- ~~ Anna Kettle, Suffolk, England |""""| ~ Lime plasterwork, plaster conservation / ^^ \ // Freehand modelling and pargeting |____| www.kettlenet.co.uk 07976 649862
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Lobster wrote:

To some extent it depends on the brick, but it's not generally a good idea outside! The brickwork can be made much more susceptible to water absorbtion and spalling. The operator's technique and the "sand" used to blast clean are factors too. What sort of bricks is the construction of? As a matter of interest, why was the render removed, and was it an original feature? If you have not too much to clean up, could you use brick cleaner (acid based)?
J.B.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.