Crumbly, soft bricks and leaky walls *PIC*

[Anonymous]

I think I've discovered the cause of an area of dampness in the kitchen of the cottage we're renovating. I climbed on the roof of a single storey section to investigate some dodgy looking areas of pointing and patching on the gable end. The area pictured is directly above the dampness in the kitchen and it seems rainwater is penetrating and percolating through the wall.

As you can see from the picture, the wall is in pretty poor shape with cracks, gaps, bee holes and very soft crumbly bricks. In one place, missing or damaged bricks have been replaced by expanded foam which was simply rendered over. I assume that all the nasty cement based mortar has accelerated and exacerbated the deterioration of the bricks?

The question is, should I cut out and relplace all of the crumbly bricks and repoint with lime mortar or can some of the existing bricks be stabilised somehow? I'm worried that once I start chopping out bricks I'll end up having to take down a large area of wall.

Also, what is the best way to deal with the existing cracked and loose cement flashings at the top of the gable? Can lime mortar be used for his purpose or is it better to use a metal flashing?

 

[Anonymous]

I would get rid of the foam and cement as a priority - this can only be doing harm. To replace or not to replace? This is a matter of judgement and how long you are prepared to spend on the work. Some bricks may be in such a state that you need to replace them whilst you might get away with a bodge on others. By that I mean facing them up with some lime mortar and crushed brick to give colour or colouring by some other means like limewash. Unfortunately these things often come down to time and economics rather than perfection. Helibar is useful in strengthening anything structurally dodgy.
Don't under stand the flashing bit so if you think my input would be useful then just explain a bit better. Hope this helps. Mike

 

[Anonymous]

Given the state of the thing, it looks like the best thing would be to lime render the wall, removing anything loose first. If you wanted to make it look nice without render, looks like a lot of work.

If OTOH thats just one bad patch on an othewise good wall, repair may be better than render.

Re the foam, it wont do any further damage to leave it there. A horrid bodge, but if its only one or 2 bricks its harmless enough. Assuming those arent arch bricks or anything similar!

NT

 

[Anonymous]

Many thanks for the helpful advice.

I've attached a further picture showing the cracks in the cement fillet which needs repair or replacement.

I have ordered some lime mortar from Mike Wye and have booked off Monday and Tuesday to tackle the job.

Any thoughts on the best approach to the cracked cement fillet? In another post I saw that Geoffrey mentioned using cement on his roof as lime mortar was too fragile. However, I think it was frost that damaged his work. Would lime gauged with Metastar be sufficiently durable provided I'm lucky with the weather?

I apologise in advance if these questions are naive but I'm very much a lime products novice!

 

[Anonymous]

We've never used Metasar (used pozzolan - we have boiler ash by the ton!) so I can't say, but it seems reasonable to me. Geoffrey used cement I think (it's a while ago) because it was winter and the lime got frosted. I think he also used cement for his chimney flaunchings (haunchings in some parts of the country) and for his ridge tiles.
We have cement fillets in a similar state to yours and will be using the same lime as we will be pointing the walls with, once we have the roof done (gulp - lots of it at horrific expense...). That can't be put off forever!

What sort of lime have you ordered? We all have our different opinions of course - but any lime (and no cement!!) is better than cement for walls, and I would suggest that the fillet is part of the wall too!

The bricks look interesting.

 

[Anonymous]

Oh - we have used lime as a fillet on an outbuilding and it's fine by the way - lime putty, sand, ash.

Everyone has their own views, too, on finishing it - our method (the SPAB approach!!) is to leave it a day, covered, then rub back the surface very gently with a fine pointing trowel. Some people use a small scrubbing brush, others like scrunched up hessian - anything to give a slightly roughened finish and expose the aggregate.

Aggregate is of course another whole can of worms, but again don't at this stage get too bogged down - you need to get a repair done, and quickly. Try to match the existing mortar as far as possible - although not the nasty cement pf course.

It's not rocket science, if you make a bit of a mess it stays soft enough to re-do, and it's very satisfying. Honestly, you'll soon get the hang of it.

 

[Anonymous]

To be honest I had two very long and involved conversations with the helpful staff at Mike Wye. I told them what I was planning to do and let them choose the correct products for me!

By the end of the conversations I'd ordered 3 tonnes of various types of plaster and mortar, a DVD, and a van load of tools! The fun begins on Monday...

I'm pretty sure the mortar is 3.5/1, described on their web site as "suitable for external building and pointing where a pozzolan such as Metastar is to be added."

Would I be best to take off the existing cement fillets and replace the whole lot with lime mortar - I guess patching or filling cracks in the cement fillet is pointless (no pun intended)?

Once the pointing and wall repairing is done I will be moving inside to start applying 2.5 tonnes of lime plaster ....

 

[Anonymous]

It sounds expensive! I've no doubt you've been given very good advice though, and I gather the DVD is useful.

I'd remove the whole of the cement and replace. I presume that eventually you are going to patch the wall anyhow, not just the bits in immediate need, so may as well do the fillet properly. If you can keep sound historic mortar do try - people remove it when there is no need to redo entire walls.

If you can't do the cracked fillet now then certainly just patch it up for the winter with more of the same, then do it properly in the spring.

 

[Anonymous]

To be honest, the cost was a little less than I'd estimated. I've become used to my budget doubling every few weeks.

If I succeed in doing the lime plastering myself and getting a decent finish then I will be saving a minimum of £4000 in labour costs. Believe it or not, the first plastering quotation I obtained was on a per square metre basis and it worked out at £12,000!

 

[Anonymous]

Well, the good thing about lime is that it stays workable for a fairly long time, so you aren't time limited as with gypsum. A slightly wobbly finish is OK in a cottage anyhow! If you are finding problems then it might be worth going on one of the day plastering courses a number of places offer - or even hire in someone for a day to show you the basics. Given what you are saving in labour etc it may be worth it if you are finding it difficult. Take your time and I'm sure it will be fine.

Many people who post here have learned to lime plaster through and carried out decent work. Best of luck. Any quieries as you go there before you and can answer!

 

[Anonymous]

It does sound expensive we were advised that a lime putty mortar mixed with metastar produces chemically an artificial hydraulic lime. A cheaper option for us was to use a feebly hydraulic lime mixed with local sand, much cheaper than buying premixed mortar with sand and water already added then adding a metastar. although after reading the linked article from mike wye (else where in the forum) i am completely confused however it is clear that he does not think much of hydraulic lime

 

[Anonymous]

I'm no chemist - but I believe that a pozzolan simply helps to set the putty and aggregate mix more quickly, although it also makes for a very slightly less porous (if you see what I mean) and harder mortar mix. It can also, however, in exposed situations, make it more resistant to weather erosion. It's still a non-hydraulic though.

I have no idea of what Metastar does. I think that hydraulic lime has its uses in certain situations, especially under water where it will set regardless, but I wouldn't normally use it for pointing and certainly not for plastering. Chimneys yes...

I'm not at all sure about French lime, however - it needs reading up on. It may have different properties,

I do know building firms who claim to specialise in historic building work who use hydraulic. I suspect that that has more to do with faster drying than suitability. I also suspect it's better than cement!

Complex stuff. Peter M-H used to chip in in these discussions and give us his expertise. He is a very sad miss indeed.

 

[Anonymous]

I tried to get onto a course that Mike Wye & Associates are running on 28/10/2005 but it's full. It's the last course they're doing for this year and I have to get the work done quickly in order to rent the cottage out.

I may well do what you suggest and get an experienced lime plasterer to spend a day giving some tips - assuming I can find someone who's willing to do this. I'm in Norfolk and it 's been a struggle to find anyone with the necessary expertise.

I have the Mike Wye DVD and several booklets and pamphlets on using lime so I'll try to put the principles into practice. As you say, I'm not looking for perfectly flat walls. Expect to see some more posts pleading for guidance if/when I get stuck!

Thanks very much for the encouragement and help so far from all who've responded to my previous requests. And thanks too to all those whose previous postings I've trawled through for tips and advice.

In all probability, without this site the cottage would by now have been dpc-ed, membrane'd, waterproof rendered and gypsum'd to death!

 

[Anonymous]

Metastar is simply a pozzolan manufactured using Cornish clay. Mike Wye suggested gauging the mortar for the pointing work and also using it in smaller quantities for plaster base coat(s) in areas of the wall which are particularly damp. They explained, as does their DVD, that the resulting mix is less breathable than would be the case with no pozzolanic additive. I guess it's a case of getting the balance right between durability and breathability.

There's more info on Metastar on Mike Wye's site (linked).



Mike Wye Metastar page

 

[Anonymous]

We have tons of boiler ash. Going free...

 

[Anonymous]

Richard - I have done thousands of sqaure metres of lime plastering over the years and have never used a pozzalan or hydraulic lime. This is simply because I have never felt it to be necessary - others may have different experiences and it is an interesting topic for discussion.
I have no idea whether hydraulic is less breathable than straight lime putty but if this is the case then obviosly you need to assess how important breathability is in whatever you propose to do.
Don't be nervous of using lime, trust it - it's a great material and I feel that good old common sense will come to your aid!
A few simple rules -
Wet down the background - not so that it's running! You want the lime to carbonate gradually but still retain suction in the background cos that's how it sticks.
No coat should be more than about 12mm thick - that includes any making good etc. and should be hard and cured before the next coat goes on.
Scratch up each coat to provide a mechanical key.
Rub up the final coat with a big handful of hessian, this is a circular motion and good old common sense will tell you when to do this. The great thing about hessian is that it does'nt matter how unflat the finish is you can still bring up the aggregate.
Chuck on a scat (or roughcast) finish if that is trad. in your area.
Apply as many coats of limewash as are necessary.
It really is as straightforward as that.
Don't be nervous - just get on with it!
If I can help further then just ask - I have'nt got a great deal else to do at the moment! Mike.

 

[Anonymous]

In a rush - yes it is less breathable - it's better than cement though! The use of hydraulic lime in many modern bulding situations would be a good thing...

Pozzolan is useful where you need a quicker cure (frost warnings) and in exposed situations.

Mike - it's pity it's the frost season or you could come and do acres of lime pointing required here!

 

[Anonymous]

Oh - pozzolan I wouldn't use generally for pointing (unless in said exposed situations - a wall which gets a great deal of weather thrown at it it may be useful). However, building with lime putty it has its uses - you can get on with job faster.

 

[Anonymous]

Adding a pozzolan of any form to a non hydraulic lime will produce an hydarulic set similar to that found in a natural hydraulic lime.

Hydraulic lime is now regarded as an essential product for historic building repair. Non hydraulic lime in some parts of the country just did not exist historically not just for mortar but also for plasters

The discription below is taken from an article found on the linked website

Simple non-hydraulic lime mortars harden by drying and carbonation, that is by the conversion of calcium hydroxide (slaked lime) to calcium carbonate by reaction with atmospheric carbon dioxide. In hydraulic mortars this hardening is supplemented by a more positive set brought about by chemical reactions between calcium hydroxide and reactive silicates and aluminates in the presence of water. In natural hydraulic limes the reactive silicates and aluminates are supplied by clay minerals in the limestone. Where a hydraulic set is required in a lime mortar and these minerals are not naturally present, or are not present in sufficient quantities, they can be added in the form of pozzolans



http://www.buildingconservation.com/articles/pozzo/pozzo.htm

 

[Anonymous]

Is it really regarded as so essential? Well, I stand corrected! I'll pass the information on then. I'm sure many who work with, and advocate, the use of line mortars will be interested in that.

You do sound, however, as though you are quoting from some advertising blurb.

Anyone who wants unbiased information regarding lime mortar, the various types, and the suitability for various different work, I suggest contacting SPAB. The helpline is free.

Also buy Jane Schofield's little book on the subject. Then read up, and make up your own mind.



http://www.spab.org.uk