Lime Render or Cement?

[Keithj]

I would appreciate the opinion of the gathered wise folks.

We are having an extension built onto our Tudor property. We've had major work done on the house itself, removing concrete that was used in all the wrong places, and replacing the oak where it was damaged as a result. That's just about complete (see the blog about the repairs if you like sad pictures).

The specification for the new build says "Lime render". We asked for that when the plans were prepared, to match the house. However, the builder missed that bit and is a fair way down the path of cement render: he has fitted galvanised metal laths all round. There is an air gap between the metal laths and the studwork/plywood/ Celotex open to the outside at the bottom, with some sort of paper over the ply. He assures us that cement applied in this way will be equally good in function to lime render, but accepts that he may have to remove the metal laths and go for wooden laths and lime render, since that's what the spec says. He has offered us a price reduction of £600 to stay with the cement render. He also says the cement render will need less maintenance in future - although we are going to have to have the rest of the house limewashed every few years anyway.

We have a decision to make. Cement, or lime? Is he right that cement will be as good as lime?

 

[Schoolmarm]

The first thing that springs to mind is will you be able to limewash cement and match your house?

Secondly, cement gets covered very quickly with surface crazing/cracks which won't self heal like lime render and will let water in. Although the gap may stop water passing into your house, it will still have the potential to cause damage to the render itself during freezing and thawing.

£600 seems a strange figure, if the quote was for cement it would cost a huge amount extra to upgrade to lime. I'm sure someone on here used galv under render but can't remember who.


Are you project managing?

 

[Schoolmarm]

Just very quickly looked through your blog. What a huge amount of work. Why have you not got the original builders to do the extension?


Tell the new builder you don't want cement but you MUST MAKE SURE they know what are doing. If they don't usually use lime DON'T LET THEM TOUCH IT.
Were the bricks laid with cement? I see the footings were.

 

[Keithj]

Yes, we are project managing the new build ourselves. I've also been giving the builder a hard time about some things that aren't being done right (as you can see from that blog). The team that did the restoration work on the house were brilliant - I learned a lot from them, and could not fault them.

We do have the original building firm doing the extension. The problem is that the boss of that firm was bullying the (brilliant) technical expert who masterminded the repairs to the house, and she left the company as the work on the extension was starting. The rest of the expert team was pulled off after the foundations were poured, and he subcontracted in a jobbing builder to do the rest. We made our opinion clear about that! This builder and his workers are nice enough chaps, but experts in Tudor buildings they aren't. They are not doing any of the work on the original house, so we aren't concerned in that regard.

The metal lath is galvanised, and the subcontractor-builder has explained that it cannot be used for lime render. If we opt for lime, it will be removed and they will use wooden laths (as have been used for the rest of the lime render).

The bricks in the extension were laid with cement, but the brickwork and internal finish on the house was done with lime.

The lime experts with the original team tell us there is no problem with matching colours on the cement. In fact, they suggested using the same limewash on the cement. It will look different when it's wet (and when it rains), but otherwise will look the same colour. There is considerable cement work on the "front extension" and on the Victorian addition at the side of the house, so it will be a common appearance.

If we opt for lime, the lime expert from the original team will be brought back to do the limework. We have total confidence in him. In fact, I understand that if we choose cement render, the same chap will do that.

 

[AMc]

If we opt for lime, the lime expert from the original team will be brought back to do the limework. We have total confidence in him. In fact, I understand that if we choose cement render, the same chap will do that.

If you've had an expert write up a spec then I wouldn't use a comparatively small saving to justify deviating from because someone didn't read it properly before starting.
I regretted several decisions in our project where I didn't put my foot down and make someone do what was specified and let them do what was easier for them.
You're the one left living with their compromise.

I'm not an expert but if you have places where the two finishes meet then I would expect Lime to Lime to behave better than Lime to Cement as the two materials have different properties in dealing with moisture, heat expansion etc. I would expect the Lime/Cement join to crack in time and lead to issues with both.

 

[skier-hughes]

Surely if LBC was granted, and this says lime, then when the CO finds out it's not lime it'll be taken off and redone at your expense?

 

[Keithj]

Happily, there isn't a lime-to-cement join, since there is a large (new) timber post where the new building meets the old. It's lime to its west side, whatever we decide to the east.

I have a call in to the CO for his view. I spoke to the assistant this morning, who thought that since it's not on the original house, they would be less concerned.

 

[Schoolmarm]

Green issues then?

If you decide to have cement you must insist on a much greater discount though.

 

[Keithj]

The conservation officer confirms that since it's not part of the old building, there is no objection to cement render.

I've looked at the priced specification, and the total for building the stud plinth wall, Celotex insulation, and render inside and out is £1,568. There's a fair bit of timber and labour etc in there, so I doubt the external rendering in the quote is much more than £600.

We still haven't decided yet. I want to ask the opinion of the man doing the rendering: he's an expert.

 

[Schoolmarm]

Well in that case, why would you want cement instead of lime?

You have used traditional stuff in the main building and I can't think of a single benefit in using cement on the extension.

£600 is a trifling amount so you may as well go for lime which will cause far less harm to the planet and will help by locking up some carbon.

 

[biffvernon]

Remove the cement quick - before it get too hard. It's just the wrong material to go anywhere near timber, old or new.

 

[Schoolmarm]

It isn't on yet Biff, OP is trying to decide which to use.

 

[biffvernon]

Ah yes - I read "the builder ... is a fair way down the path of cement render" as he was half way up the wall, whereas he's still walking up the path.

No-brainer then. Tell him to stop right there.

 

[Lime]

Well in that case, why would you want cement instead of lime?
You have used traditional stuff in the main building and I can't think of a single benefit in using cement on the extension.
£600 is a trifling amount so you may as well go for lime which will cause far less harm to the planet and will help by locking up some carbon.

I quite agree.

 

[Keithj]

Thank you all for the advice. Decision made: sorry, Mr Builder, but it has to be lime.

 

[skier-hughes]

 

[MatthewC]

I love your blog - and I think you've made amazing progress with the house, considering the original condition. I'm not clear about the area concerned re cement or lime render - £600 doesn't sound like much for lime, so I guess it's quite small?

Stick to your guns - if you compromise with cement you will regret it later. I had numerous people saying I should do things like use plastic guttering, re-plaster with gypsum/plasterboard, install a chemical DPC, install a cement kitchen floor, etc etc.

Matthew
http://houseintheenchantedforest.blogspot.com/

 

[Keithj]

Yes, the area in question is on the new build - the Garden Room - and is the area from immediately above the brick course to the level of the windows, plus the walls adjacent to the house. I would guess it's roughly a metre high by 12 metres long round the outer part, plus end walls around 2m wide by 3m high - a total of maybe 36 sq m.

Anyway, the builder now knows it's to be lime rendered. He has first to remove the galvanised metal mesh and replace it with stainless.

 

[Keithj]

The metal mesh came off, and the chap doing the lime work said "no" to stainless steel. He asked for (and got) the same timber lath that is used on the house. The first coat is on, and looks excellent.

He fixed oak strips to the corners to render up to - in preference to rendering round an outside corner.

There's no substitute to using true professionals, is there!