Fill around flue for Chimney Construction

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Wolverine

Registered User
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Hi All,

Bit of a dilema - House being built at the moment.
It's a two storey, currently up to joice level.


Brother in law is a blockie for 20 yrs, and has been calling now and again to keep an eye out.
He spotted something over the weekend.

He noticed that the filling around the chimney flue was not a sand & lime mix.
It appeared to be sand only. It was wet at the moment due to recent rain but he was 100% certain that there was no lime wixed with the sand, and he feels there should be.


He advised me to get onto my engineer and get him to contact the builder and get a block knocked out, drain the sand out, put block back and fill again.

Rang engineer - he's on hols for a week to 10 days.

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After some thought I decided to ring the builder. they havent started the other chimney yet but should be this morning - so I felt It'd be better to ask him now when he had half a chimney built rather than 1-1.5 built.

Anyway - I told him the storey and he said that they stopped using lime about 5 yrs ago, and they now use a fine cement & sand mix.

I told him that the brother in law said I should get the thing re-done by taking a block out and draining it, and the builder said that the cement at the bottom would be hard by now.


Am I being conned ?
Or is the builder telling the truth - Do they not use lime anymore ?
I looked in the homebond book and it too mentioned lime.

I asked him if he could use it from now on, and he said no problem.

Any advice is appreciated.

Regards,
Wolverine.
 
Check the http://www.environ.ie/DOEI/DOEIPol.nsf/wvNavView/wwdConstruction?OpenDocument&Lang=en (DoE buildings regulations/standards) to see if they specify what should be used in this context.
 
The traditional mix is a 1:1:12 (Cement:Lime:Sand) mix (as outlined on page 110 of the Homebond Manual). This weak mix would allow for expansion and contraction of the flue liners when they heat up/ cool down. The addition of lime is primarily for reasons of workability. Cement lean mixes are difficult to work with (they are stiffer and there's no "fat") so it is usual practice to add lime or plasticiser to improve their workability.If your builder has used an equally weak cement only mix I imagine it should be okay, but I think the addition of lime in any future work is probably best. It should be realitvely easy to ascertain the strength of the mix used already- if weak it will easily be displaced with a masonry nail or similar and a weak mix will allow for the thermal movement anticipated once fires are lit. In the past it was common for flue to be (erroneously) packed with dry sand (no cement or lime at all) which resulted in problems later- this would be more worrying if it were the case.
 
Thanks Guys.

Carpenter - The brother in law was able to dip his hand in a grab a fistfull of the stuff. He seemed to think that this was wrong, and should be corrected.

It's looked like normal wet sand, and without any force it fell apart in his hand like any bit of wet sand.
Should this happen ?

Has the builder kinda cut a corner here by not using it ?
or is it as he said - they've stopped using lime in the industry for last 5 yrs and they now use a lean or fine cement mix ?

I've looked in the building regulations and can't find any reference to it.
I've seen it in the homebond book alright.


Thanks Again,
Wolverine.
 
Lime is still in use in building but it has certainly been supplanted somewhat by more modern mortar additives such as SBR and plasticiser. I don't think he would be trying to cut corners by omitting lime- lime is cheap and adding it to the mix would entail no additional effort or cost. A weak sand cement mix (1: 12) should stay firm but crumble when compressed. Take a sample and dry it indoors- if there is some cement content the sample should hold it's shape and crumble when compressed, unlike pure sand. If in any doubt ask you builder to confirm (in writing if needs be) the materials used are fit for the purpose. If no cement was used your brother in law is quite correct in his assertion that the material should be removed and the packing re-done to your specification.
 
Hi All,

Just dragging this old post up because I wanted to ask a quick question about chimney filling. My blocklayer is about to fill the chimney and he has suggested using a new product that arrives in bags like cement and is simply poured down the outside of the flues straight out of the bag. He said it was recommended to him and its supposed to be 'great stuff'. Does anyone know the name of this as I'm gonna order it from the hardware soon! I suppose the hardware will know its name but has anyone any advice on this stuff!
 
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