Interesting question for lime purists

[Ian Bond]

I'm not a fan of the plastic tubs for a start, and have been unable to find anyone to recycle them

Building firms who do both modern and conservation work just re-use them as mortar buckets.

Many thanks for those very interesting replies. I'll wait to see if any more come in before I post any conclusion myself.

True Piper, and I do this myself. The trouble is, there's only a small percentage of the total that can be reused in this way. I wonder how many are going into landfill?

The tubs are convenient for doing work in small batches, and for overcoming difficult access issues.

The tubs I've used are recyclable polypropylene (coded PP05 or P 5 on the base of the tub). I did find a plastics recylcing firm, but they were unwilling to take the tubs that had been anywhere near sand or mortar. I said I'd wash them clean, but was still hearing a big 'no thanks' over the 'phone.

It'd be great if the lime suppliers would take them back for reuse, but I expect that's an additional cost to their business (and extra work) that they don't want.

Or I could try to get bulk bags of lime or mortar, and transfer each load into a stock of tubs that I constantly reuse.

I've noticed that some supplied supply small plastic bags of lime products instead of tubs. I suppose they pack down into less landfill space, but it's still polluting plastic.

Ooops, Rachel de Strawhouse said "We don't use the C-word here", on last night's Grand Designs.

I liked her C word retort, and her straw bale house too. Good to see natural building products being used so successfully in a modern 'traditional' build rather than 'just' for repairing a house from a bygone age

I should add that the builders are a main contractor - well respected and high-quality local firm, who have experienced lime workers on their staff and have done conservation work for EH as well as many smaller local lime jobs.

If they're willing to discuss your concerns and adapt their approach to the requirements of both the building, and their client, rather than just doing a "I've been doing it this way for 20 years, and only c*m*nt will work" , then you'll be on the right track.

Best of luck with it - it must be a quite a test of nerves at this stage of the project, judging by your pictures and the current well ventilated state of your house.

Ian

 

[Flyfisher]

Lime also absorbs some CO2 as it carbonates - how much I don't know off hand.

I believe it reabsorbs ALL the CO2 driven off in the kiln process. I think this was taken into account with the '20% less than cement' figure.

I missed grand designs but I like the 'C-word' comment. Mind you, I don't think I'd describe lime as a 'natural' building product - traditional, yes, but quite definitely man-made.

 

[Ian Bond]

OK, slight correction - natural building technology, as opposed to modern industrial methods.

Although today's lime products are modern industrial products - I'll give you that!

 

[Nemesis]

http://www.strawbalefutures.org.uk/

In case anyone wishes to DIY...

Vote on May 8 for the Penwhilwr strawbale
house co-designed and co-built by amazonails
in the Grand Designs Eco Home of the Year Award

http://www.amazonails.org.uk/

 

[piper]

If they're willing to discuss your concerns and adapt their approach to the requirements of both the building, and their client, rather than just doing a "I've been doing it this way for 20 years, and only c*m*nt will work" , then you'll be on the right track.

Best of luck with it - it must be a quite a test of nerves at this stage of the project, judging by your pictures and the current well ventilated state of your house.

Many thanks for the replies to this one, particularly Ian.

The alarming hole has now been built up either side with concrete blocks, well built in to the stonework of the old flue, concrete lintels across the top, and the blockwork continued up to support the roof purlins - modern methods, but quick, and the structure is now safe. The mortar mix is 5:1 so not too strong. The builder in daily hands-on charge of the project said "some of the lads think just bang in more cement to make it strong, but that's not neccessarily true".

I'm definitely going to stay with the original plan to have the rest of the wall rendered in lime. As I see it, the arguments are the same as for the outside walls - blending old stonework in with new blockwork, and also not putting a stronger and more impervious material (modern cement render and/or gypsum plasters) on top of the existing lime mortar between the old stones. I hope those here with more knowledge and/or experience agree. The replies I've had at least confirm that I'm not being foolish to stick with the lime spec. in spite of all the new concrete work.
The builder and I have certainly discussed the concerns a good deal, and he's very open to the idea of using lime, while not claiming to know a lot about it. Others who work for the firm have more experience, having worked on more of their conservation jobs, so he'll be consulting them; in fact they will probably be doing it. To give him his due, he has been very good at adapting so far.

The main problem, as he explains it, (apart from labour cost) with not using the standard block and cement method for the structural support work, is that from the company's point of view (insurance, guarantees of their work, contract details etc.) they have to have professional, qualified assurance that the mortar mixes and building methods used are going to deliver the required strengths. Just going on the client's on-site opinions (no matter how well-informed from PPUK!) is not enough, though at least for pointing and rendering, the project manager higher up the building firm's hierarchy is quite used to the conservation jobs they do with lime putty.

This is probably a general problem with building contracts - these "new-fangled" lime specifications have to be more widely professionally endorsed before most general builders will use them.
Our architect has specified lime for the outside render (his idea - he has been on a short lime course at Womersley's) and also for the rendering of this inside wall (my idea) but "details of mix and finish to be agreed with the client on site before proceeding". He says I've researched it more than him.
I think I'll defer to the main contractor's experience on other jobs for the outside render (weakly hydraulic? - what are the opinions here? We get a lot of rain) but for the inside I guess it's the standard 3:1 mix of sharp sand and putty for the first coats, and a richer mix of lime and fine sand for the finish. Am I right?

 

[biffvernon]

Thread on Grand Designs strawbale house, featuring comment from Rachel herself, at http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1674&page=1#Item_12

 

[Ian Bond]

Hi Piper

As I've already said that I think your approach is good, I'll leave it to others to others to add their comments.

As to the use of modern materials in preference to lime, I can understand why they are almost universally used: cheap, widely available, easy to use, predictable, get the job done quickly.

The older methods may take longer, and perhaps cost more if you are paying for specialists to do it. But they're proven technologies, evolved over millennia.

Of course there's been a loss of this knowledge over several generations now. Your architect himself admits that he's deferring to you.

But at least your builders have the relevant experience with traditional methods and are willing to go along with what you want to do. Without chucking in some cement when you're not looking, because they know better.

 

[piper]

Thank you, Ian, for that boost to my confidence.

Without chucking in some cement when you're not looking, because they know better.

What they actually want to do is chuck in some yellow builders' sand, because they say sharp sand alone doesn't have enough fine grains. Do I insist on sharp, and only let them use fine sand on the finish coat inside - when it should probably be silver sand anyway?

 

[biffvernon]

There might be something in that. Ideally you want aggregate that comprises a range of grain size from coarse to fine. A washed 'sharp' sand might not have the proportion of fines you want.

 

[Ian Bond]

I've only every used sharp sand for both the coarse render and brick/stone laying.

For fine plastering (and making mastic) I've used kiln dried fine silver sand with no problems.