Sand in chimney flue, possible causes?

jack of all

I remodelled the old open fire and fitted a new stove, complete with new hearth, over mantle etc over a month ago. It's been in constant use for a couple of weeks now and I'm very pleased with the set up, given that I'm burning less than half what I used. However there is one little niggling concern- I've found some very fine sand in the 90 deg bend at the back of the stove, on two ocassions over the past week. The sand is very fine and clean. First time this happened I reckoned it was due to some old mortar being dislodged from inside the flue. (The house is 10 years old and there were some hardened mortar droppings on the flue which could not be dislodged). If this is the case- great, if not I'm worried that the actual parging or filling arouind the flue liners may actually be trickling into the flue. I can't understand it though, this flue has been in use over ten years previously and we never had a problem. It's very strange. I'm going to monitor the situation for a few weeks and see if there's any more sand in the bend. Just wondering am I missing anything here?

yop

Its odd. Have you cleaned away the sand and does it come back?

jack of all

yop wrote: »

Its odd. Have you cleaned away the sand and does it come back?

It's very odd! I know the house is pretty solid and fairly well constructed (I'd be very surprised if neat sand was used to backfill around the flue liners). I removed a cupfull of sand the first time and perhaps a half cupfull last night.

JamesM

I haver seen very fine sand around flue liners. Not too often, but I have seen cases where it has blocked the 90 degree bends leading out from oil boilers. Maybe you are getting more heat than before from your stove and it has cracked the liner - or cement at the joints.
Jim.

jack of all

Interesting Jim, I thought that the flue gases would be cooler from the stove given that the stove is more efficient than an open fire? When I looked into fitting the stove this was one of the chief reasons put forward for fitting a new stainless steel liner (I didn't do this anyway). The chimney breast is certainly a bit warmer- but the stove is producing fantastic heat (although not overfired- I'm reluctant to overdo it). When I had the open fire I had an 18" fire back (2" wider than normal) with matching grate, so I had big fire, with coal the lot! Never had a problem with the fire before now and never noticed anything come out of the chimney other than soot! I'm wondering is the "sand" a fine residue from the EcoBrite I burn- could it be blowing up the flue and then settling in the bend? All I know is if I have to take out the stove and reline I'll cry!

JamesM

Flues and chimneys are not really my field, so I am only guessing on the cause.
I have mainly seen the sand in purpose built solid chimneys in boiler houses.
In these cases, I presume that the liner has cracked and the sand gets into the flue.
I hope that Iam wrong and it is only a deposit from the fuel you are using.
Jim.

jack of all

Cheers Jim, my only option at the moment is to monitor the situation for a few weeks and see what happens- if the issue persists I'll have to investigate further.

RKQ

A weak sand / cement mix is used around clay flues, in blockwork chimneys.
Sometimes a very weak mix is used, which looks like dry sand.

Any work on the flue has dis-lodged the seal around the fire top. This sand will continue to seap down - bit like an egg timer.

Seal around the flue, 90 bend, fire top etc to prevent sand escaping.

jack of all

Thanks, I'm familiar with masonry chimney construction- thing is I carried out no physical work to the chimney other than to fit a 5" steel to clay adaptor! No damage was caused to the liner in fitting, so I'm really baffled!

RKQ

Maybe the flue is cracked?
The fine sand wouldn't be noticed in the ash of a solid fuel fire.
Best of luck.

jack of all

The stove is coming out tomorrow to examine the source of the sand (after I removed another cupful today), if the liners are sound with maybe a gap in the mortar to be filled I'll make good with fire cement (local chimney expert suggests this remedy). Otherwise I'm looking at €2000 or so for relining with a multifuel liner!

Heatherview

Hi Jak of all
Wheh you take out stove check the following

1. Are the flue liners sq edge or rebated in chmney.

There may be one cracked or leaking at a joint and letting filling in ? Can you shine torch up chimney to investigate. If your house is reasonably old the flues would be just square edge and relying on mortar joint only. I think this could be your problem.

Good lUck
Heatherview

jack of all

Spent all day Saturday taking out the stove, making good and refitting, whilst trying to keep the new (light coloured) carpet clean! Filled a joint in the flue liners which appeared to be open and a tiny hairline crack. Did a very thorough job and was pretty pleased with the finished job (even beeter second time round!). I was 99% sure that this would cure the problem, but I was to be disappointed when I found a half cupful of sand in the stove the following day. To say I was gutted would be an understatement! I'm convinced the problem lies higher up the flue, well out of reach and this problem has most likely been there since construction and is in no way connected to the stove installation. All very frustrating and a waste of a Saturday to boot. I'm going to talk to a fireplace man at the weekend to discuss the options open to me. Thanks for all the replies anyway.

RKQ

Sorry to hear that!

"Filled a joint in the flue liners which appeared to be open and a tiny hairline crack". There must be a crack in another flue liner, further up.

jack of all

I've been lighting fires every night and (touch wood) haven't had any more sand in the flue for the past week or so, very strange...

RKQ

Hopefully the problem is solved.
(Maybe the hairline crack / gap allowed sand to fall when the flue was cold. Now that its being used, its expanded, closing the gap?)

jack of all

Who knows? I'm happy enough for the moment...