Minor repairs with lime mortar

[dent]

Hi all,

I live in a 1950's house. It is in a small village near Bath, and so was built in cast-stone blocks which resemble surrounding houses (which are Bath stone). The mortar used is very light - almost white - and powders easily if rubbed, which leads me to think that it may be lime mortar. Is this likely? I thought that lime mortar was only really encountered on pre-1930's houses, and not on more recent buildings? At some point, another owner has added a porch, and the mortar on that is still very light, but with a distinct grey tinge, and is very hard to the touch (it doesn't powder when rubbed), so this would appear to be cement based.

My main question is this. There are various places around the house where I need to repair the pointing, and fix some ugly holes that the previous owner filled with grey mortar. I am also replacing my doors and windows, and need some mortar for bedding down the doors, and making good in a few places. Should I try to obtain suitable lime mortar for this work, or could I use cement mortar? Obviously if I used cement mortar I would have to use suitably coloured sand, and white cement - would this be a close enough match?

I haven't been able to find any local suppliers of lime mortar (although living near Bath this seems odd). Getting small quantities of lime mortar mail order I end up paying twice as much for postage as I do for the materials!

thanks,

dan.

[The Natural Philosopher]

More likely its just shoddy cheap mortar that never had much cement in it to start with

I thought that lime mortar was only

I have used a LOT of white cement and sand mixtures..it comes out very nearly white. I have also added lime to it. It all works pretty well. I even ran out of cement one time and made a mix that was nearly all lime and sand..it worked after a fashion..its still a bit soft even today, but it holds up well enough.

I think my favorite was 1 cement 1 lime and 6-10 sand. Measured in approximate shovelfuls.

Use more cement if building below the damp course..it makes the cement less porous and water ingress is reduced.

You can use silver sand,but I found the ordinary yellow stuff was the right color for me. I also used a lot of sharp sand to get a gritty mortar to gibe a period feel.

Your applications are not so critical that I would be overly concerned about ultimate strength etc. Get some materials and mix up some batches and try and get a color match.

No! simply buy white cement and hydrated lime from the BM..and sharp sand. Get making mud pies with it till it looks right. Then just use it.

[Stuart Noble]

Lime putty has to mature like fine wine. Best prepared in the Cotswolds by someone with a beard and a check shirt

[The Natural Philosopher]

I don't like beards or check shirts. I'll stick to bags of industrial grade cement and lime thanks.

Most real ale and mead is also atrocious rubbish

Lime putty belongs in a museum. Or someone repairing one.

[Anna Kettle]

Yes

Cement certainly became fashionable after the war when people wanted quick builds, but lime skills were still around in the 50s

Yes. But then I would say that wouldnt I! The critical thing is that the mortar must be weaker than the blocks. Had the blocks been real Bath stone then lime mortar would be important cos Bath stone is quite soft

Chard Builders merchant in Bristol is a manufacturer and supplier. Its good quality stuff but they do tend to sell it too young so I suggest you buy it now and do the work when the weather improves. Meanwhile you can do a few trial mixes with various sands to get a good colour match. Just mix 1 putty : 3 sand and put somewhere to dry out

Anna

[abaker]

I would avoid the use of cement based mortars for repointing and repairing patches. As has been said already, the mortar needs to be softer than the stone/brick else it will cause more damage to that material than vice versa. I would also be tempted to use lime on anything damp - yes it will allow more moisture in but will also allow the fabric to shed its moisture in warmer weather.

Purchasing lime can be expensive, only because of the delivery charges. However it will last indefinitely so long as it is kept from freezing and is kept in an air-tight container, so is always useful to have around. Purchase a tub of lime putty and get some sand from a builders merchant. Mix them yourself.

Mike Wye, Ty Mawr and the Lime Centre (W> >

[meow2222]

Lime is available from any builders merchants, and many diy sheds, such as B&Q, but not wickes. Its hydrated bagged lime.

There are 2 ways to use it

1. Mix lime to a sloppy putty with water, cover it airtightly, leave it at least a day, then mix with sand to use.

1. Mix dry lime powder and sand 3:1, add water and use right away.

When the mortar is green, ie solid but not hard, brush the surface to remove excess whiteness. This exposes the aggregate.

Lime has a few advantages over cement, and the disadvantage of slow setting. It should not be frosted while setting, so exterior lime work is usually left till a bit later in the year, or covered with a sheet for a few days if frost is expected.

Dont mix cement in with lime, as most cement:lime mix ratios are prone to cause premature failure.

Forget the posted tubs of expensive lime mortar, there's always someone willing to pay more for something. Lime is cheap.

NT

[The Natural Philosopher]

Thats probably true on extreme situations, but my mixes have all stood up well. The advantage of some cement is that it sets to a decent strength quicker. You don;t want to have to wait three days before you can add another course.,

My sentiments exactly.

Most mortar is only a way of keeping the bricks apart anyway. Ultimate strength and exact engineering quality is often far less important than appearance.

hydrated lime in a fairly sandy mix looks pretty authentic. Add a bit of cement and it also sticks better and is harder..

[Anna Kettle]

Lime mortar requires air to set, cement is a very fine powder and tends to block up the air holes in the mix so you run the risk of a) poor lime set cos the air cant get to it and b) poor cement set cos you didnt put much cement in After a number of failures with cement/lime mortars English Heritage commissioned a research profect on this and since then cement/lime mortars have been banned in work done for EH. Some people like NP have used cement/lime mixes with no problems but there is a risk of failure. As others have said, bricklaying is not a very testing situation cos mostly the mortar is there as a spacer. I wouldnt want to use a cement/lime mix for rendering a wall

The one exception is a cement lime mortar with plenty of cement in it. This is actually a cement mortar as the lime is not there to do any setting. It is there purely as a plasticiser. These days most people use Febmix instead of lime

Again its horses for courses. Hydrated lime (not hydraulic lime, thats something else) can be OK. It MUST be fresh and kept in a dry place. For bricklaying it can possibly be used from the bag (dunno, never tried) but for rendering you want something with more plasticity in which case either

a) Use lime putty mortar or b) Mix the hydrated lime and sand and water to make up the mortar, then store in buckets covered in water and it will turn into lime putty mortar. The longer you can store it the better. One day is better than none. One month is good, three months better. This is a very cheap way of making lime putty mortar, about 1/7th the price but it requires a bit of advance planning

Anna

[meow2222]

I read the research on it and it has nothing to do with extreme situations. Some non 1:1 lime cement mixes do survive ok, sometimes they dont. None are reliable other than 1:1 c:l.

The advantage of some cement is that it sets to a decent

Yes, but I dont see how thats relevant to repointing, and the price of premature failure isnt worth it imho.

I dont think he plans to. And you dont with just lime anyway.

So I'm always told, but I've used old lime without any problems. Its true that some old lime could have gone off, just like old cement can, this can be checked for easily enough though, just put a dot of your lime mix somewhere and come back when is set. If ok, go ahead & use.

Lime straight from the bag can produce minor surface imperfections, which arent an issue with repointing.

NT

[The Natural Philosopher]

No, in that I agree.

Yes, also done that. Its a very nice mix. I'ts also WHITER.

Yes. I just shoved it into the mixer with the sand and cement.

but for rendering you want something with more plasticity in

Good trick.

[Nicknoxx]

Anna Kettle wrote: snip useful lime advice.

Anna, can you recommend a book or course for learning more about building lime. I've just bought a 17th century listed building and feel sure it will become essential knowledge?

Thanks

[The Natural Philosopher]

You will need more than a book on lime mortar..be prepared to find every repair is three times what it would be if it were not listed..or more.

You probably need a course in carpentry more than anything..unless its one of the very few brick built 17th century houses.

The other huge bugaboo is the listing people. And the BCO.. who will often give you completely contradictory restrictions.

A course in anger management and people management skills is recommended ;-)

[Nicknoxx]

True but Anna is a known expert in this field.

.be prepared to find every

Carpentry skills at the ready.

Yes I'm aware there may be conflicts, who takes priority?

WHO ASKED YOUR F****IN' OPINION,EH ? :-0

[Anna Kettle]

Hi Nick

"Building with lime" by Michael Wingate & Stafford Holmes is the best book for an overview and lots of background information

For really basic practical stuff like mixes get Jane Schofield's leaflet called um "Lime" I think

There are several courses around the country, where are you? I think the best value courses are two or three days with lots of hands on and only as much theory as necessary to do the hands on, plus a telephone helpline for when you get home and encounter real life problems

Anna

[Nicknoxx]

Hi Anna Thanks for that. I'll look out the books. I'm near Bath

[Anna Kettle]

Hi Nick

Ty Mawr Lime in South Wales is probably the best place for courses then. Lovely people, very inspirational!

Anna

[meow2222]

[Nicknoxx]

Thanks - bookmarked

[Nicknoxx]

Thanks I will.