black tar........

[Dibbo]

Hi, probably an old one this but I cant find any reference to this....we have black tar running down the outside of our chimney from the fire. We burn excel nuggets and wood. The wood is supposed to be seasoned but you never can tell really. Its ruining the roof and paintwork. Anyone any ideas as to causes? Ta

Dibbo

[Dibbo]

Hi, probably an old one this but I cant find any reference to this....we have black tar running down the outside of our chimney from the fire. We burn excel nuggets and wood. The wood is supposed to be seasoned but you never can tell really. Its ruining the roof and paintwork. Anyone any ideas as to causes? Ta

Dibbo

[churchward]

it can be a number of reasons. A selection could be:

 

Wood not seasoned and still sappy

stove burning too cool it should be running about 300-400 degrees F to burn efficiently.

Edited December 9, 2014 by churchward

[Keeping Up]

Do you have a double-skinned chimney? If not, this will happen. You need either a double-skinned chimney or a separate inner liner.

 

If you have a double-skinned chimney, is the inner a good fit inside the flue? Most mass-produced double-skinned chimneys have an inner which is far too small (so it will fit inside any size flue) and therefore don't work properly. If so, stuff the gap between the inner and outer with rockwool or spray in some fireproof expanding foam (available from all good diy stores)

 

If you have a coolie-hat on top of the chimney, remove it otherwise a small amount of tar will condense on the underside and drip onto the roof.

[kevinl]

Incomplete combustion, you're burning the fire at too low temperature and distilling all the tar out of the fuel before it burns, that condenses when it hits the cold air and turns into gunge. Either run the fire hotter so it burns clean, put less fuel in but more often or get a double skinned chimney so the gas exits before in condenses.

Aldi were selling flue magnetic thermometers for under a fiver, the lower zone is marked as the "creosote" area i.e. where you're distilling the fuel before you burn it. Try some different kinds of nuggets they don't all burn the same, if it's coming from the wood then a twin walled chimney might help.

K

[John V]

some types of wood even if seasoned are more prone to it I think Leylandii and some other conifers fairly bad as they have a high creosote content......also if wet (as opposed to green) seems more of a problem

[Athy]

Have you got a single-skin chimney? A double-skinned one is widely thought to reduce oozy tar seepage misery.

[LEO]

Hi,

 

Sounds as though you need a decent double skinned chimney, which allows condensation to run back down the chimney to the fire.

 

Can be purchased but easily made yourself.

 

L

 

Athy beat me to it....

Edited December 9, 2014 by LEO

[Phil Ambrose]

My vote too is for a double skinned chimney, I would also add, lose the coolie hat, stuff condenses on the underside and drips onto the roof. I had a bit of a problem even though I had a double skinned chimney, getting rid of the coolie hat sorted it.

Phil

[dmr]

If you are a liveaboard then its difficult, though not impossible, to avoid a bit of a tar stain down the side of the boat. Together with the bags of coal and pile of logs on the roof it is just another sign that you are a liveaboard boat. One boat down here on the K&A has cleverly incorporated it into the paint scheme.

 

.............Dave

[Mac of Cygnet]

Ah, but the OP says the tar is running down the outside of his chimney. A double skin chimney sends tar back down that would otherwise run down the inside and out the base of a single skin chimney and onto the roof.

 

I can think of only two reasons why tar would run down the outside of a chimney:

 

1. The chimney has a small split it in. Have a good look to see exactly where the tar is coming from.

 

2. As Phil says, it can be dripping from a coolie hat, especially in wet or cold weather. I take mine off whenever I light the fire (or whenever I negotiate an overhanging branch!)

 

But a double skin is advisable nevertheless.

[Dibbo]

Thanks for info so far...we have as double skin chimney, a tall one too. Will try it with out coolie and see. It also gathers at the base between the collar and chimney... Fire tends to be reasdonably hot as only form of heating as such. Do agree with dmr as we are live-aboards.....

[Señor Chris]

You could try high-temperature silicone sealant around the chimney/collar join.

[kevinl]

Incomplete combustion, you're burning the fire at too low temperature and distilling all the tar out of the fuel before it burns, that condenses when it hits the cold air and turns into gunge. Either run the fire hotter so it burns clean, put less fuel in but more often or get a double skinned chimney so the gas exits before in condenses.

Aldi were selling flue magnetic thermometers for under a fiver, the lower zone is marked as the "creosote" area i.e. where you're distilling the fuel before you burn it. Try some different kinds of nuggets they don't all burn the same, if it's coming from the wood then a twin walled chimney might help.

K

[Mac of Cygnet]

You could try high-temperature silicone sealant around the chimney/collar join.

That would make the chimney very difficult to remove, for low bridges, etc, and the seal would be broken whenever you did remove it.

 

However, tar gathering at the base between collar and chimney means that the double skin is not doing its job, because smoke and tar are percolating up the outside of the inner skin and over the top of the collar. This last is where you want to seal it, by stuffing fireproof material up between the inner and outer skins so that it forms a barrier when the chimney is fully seated over the collar. I use scrunched up cooking foil, but rockwool would also be suitable.

[Mac of Cygnet]

This topic is duplicated. I've reported it so the OP can have all his answers in one place.

[bizzard]

Virtually all of the goo oozes out from between where the chimney overlaps the collar flange. Stupid in my opinion. Just find a bit of pipe a loose fit and silicon it lightly INSIDE the collar orifice, problem sorted. Make sure your coal and wood is dry.

[valrene9600]

"Edited as my link is not working. Big fingers and small phone

Edited December 9, 2014 by valrene9600

[valrene9600]

http://boatlife.blogspot.co.uk/2012/11/is-your-chimney-messy-killer.html?m=1

 

Hope this works./

[john6767]

That would make the chimney very difficult to remove, for low bridges, etc, and the seal would be broken whenever you did remove it.

 

However, tar gathering at the base between collar and chimney means that the double skin is not doing its job, because smoke and tar are percolating up the outside of the inner skin and over the top of the collar. This last is where you want to seal it, by stuffing fireproof material up between the inner and outer skins so that it forms a barrier when the chimney is fully seated over the collar. I use scrunched up cooking foil, but rockwool would also be suitable.

I filled the gap between the inner and outer on ours with high temp expanding foam, that stopped stuff going up between the 2, condensing and running out of the bottom.

[LoneWolf]

Thanks for info so far...we have as double skin chimney, a tall one too. Will try it with out coolie and see. It also gathers at the base between the collar and chimney... Fire tends to be reasdonably hot as only form of heating as such. Do agree with dmr as we are live-aboards.....

 

it sounds like your flue and the inner skin of the chimney may not be fitting together properly allowing the smoke to get between the skins of the chimney where the tar is forming and running down

 

Make sure the inner skin fits inside the flue pipe (or, i suppose, the other way round) so the smoke cant escape the inner skin

 

Before too long if it's not sorted, you'll have tarry stuff running down the flue inside the boat - it's pretty corrosive i think and seems to get through plumba flue eventually.

[LoneWolf]

That would make the chimney very difficult to remove, for low bridges, etc, and the seal would be broken whenever you did remove it.

 

However, tar gathering at the base between collar and chimney means that the double skin is not doing its job, because smoke and tar are percolating up the outside of the inner skin and over the top of the collar. This last is where you want to seal it, by stuffing fireproof material up between the inner and outer skins so that it forms a barrier when the chimney is fully seated over the collar. I use scrunched up cooking foil, but rockwool would also be suitable.

 

I think you're right about where the smoke is causing the problem but surely stuffing stuff in the chimney is just a bodge to soak up the tar. I don't think smoke should be getting between the skins in the first place. it should go from flue to innerskin without any leaking

 

I think with your method the OP will just be storing up problems for himself as he wont be noticing the tar problem but it will be sitting on the collar seal and working its way through until it runs down the flue inside and makes a godawful mess

 

And the chimney will corrode pretty quick i'll bet

[Mac of Cygnet]

I think you're right about where the smoke is causing the problem but surely stuffing stuff in the chimney is just a bodge to soak up the tar. I don't think smoke should be getting between the skins in the first place. it should go from flue to innerskin without any leaking

It's not just to soak up the tar. If the seal is good it will stop the flow of tar-laden smoke up and over the collar. No flow = no deposits.

 

The only way no smoke will get between the skins is for the inner skin to be a tight push fit into the flue - very difficult to achieve unless custom made.

[LoneWolf]

It's not just to soak up the tar. If the seal is good it will stop the flow of tar-laden smoke up and over the collar. No flow = no deposits.

 

The only way no smoke will get between the skins is for the inner skin to be a tight push fit into the flue - very difficult to achieve unless custom made.

 

maybe i am misunderstanding what you mean. So you stuff the space with rockwool surely smoke will still.... oh hang on - maybe i dont know what rockwool is - is it solid? if so apologies, i can see how that would help. I think there may still be a small problem over time though

so when you say you stuffed it with crumpled foil you really packed it in tight?

 

Agree with the second - i've just redone my flue to achieve just that. I had to take the pipe to an engineering workshop anyway to put a bend in it so i took the chimney as well and they skimmed it to fit. I was probably lucky to get a flue pipe that was just too small to take the chimney

 

 

edited to add: i have now googled rockwool and had a think over tea & crumpets and have decided i was wrong to call it a bodge, sorry for that. I think it is an additional defense due to the difficulties of getting a proper flue/innerskin fit. I'm going to incorporate it into plan: Stop tar getting in the boat (which seems to have become Plan:completely refurb the stove area)

 

That rockwool stuff looks just like the tar stained stuff i pulled out of the collar seal. I'm going to stuff some in the inside space round the collar i think

Edited December 9, 2014 by LoneWolf

[valrene9600]

As I said in my link above it lasts for years. Easy to remove for chimney cleaning just lifts straight out leaving main chimney in place that is also easy to lift off. Cheaper than a double skin chim that you then have to pack with stuff to fill the gap.

Only time it will leak again is in my example link when after quite a few years the inner starts to corrode I have spare plates and can make a new one in 30 minutes.

Get a stainless steel chimney and your problems are over.