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			<title>Green Building Forum - soot/tar coming through lime plaster</title>
			<lastBuildDate>Sun, 24 May 2026 17:13:37 +0100</lastBuildDate>
			<link>https://www.greenbuildingforum.co.uk/newforum/</link>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3239#Comment_3239</link>
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		<pubDate>Tue, 15 May 2007 17:57:11 +0100</pubDate>
		<author>Rachel</author>
		<description>
			<![CDATA[Hi, a friend has been working on an old house. There was old soot coming through the chimney wall, and it's been hard to stop it coming through the lime plaster. He tried manure then lime, which usually works, but the soot is still coming through... any suggestions?]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3241#Comment_3241</link>
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		<pubDate>Tue, 15 May 2007 18:42:28 +0100</pubDate>
		<author>tony</author>
		<description>
			<![CDATA[Not easy the problem is tar. The chimney has had lot of smoke and tar going up it in the past and this has leeched into the mortar and is now on its way out through the plaster. Most likely this tar contains both oil and water soluble fractions. Is the chimney still used? If so it will need lining. In any case the best plan is going to be to construct a new wall as thin as possible which has no contact ( battens will be OK ) with the problem area. Isolation is the name of the game. The alternative is to rebuild the chimney.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3247#Comment_3247</link>
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		<pubDate>Tue, 15 May 2007 22:05:51 +0100</pubDate>
		<author>chuckey</author>
		<description>
			<![CDATA[Over on the period property forum there is exactly the same discussion going on. I have this problem with tar coming through some "Knauf" finish plaster thats 5 years old.  I am hoping that when I am ready to decorate the room, that a coat (or two) of stain blocking paint will hide it prior to papering. The first thing is not to generate any more tar, line the flue/discontinue using the open fire. It is extremely unlikely, but in the event of moisture carrying the stain with it, dry out the flue, i.e. cap it and ventilate it.  You can see the limestone blocks on the cottages are black from the tar leaching through them over the years (200+) but the lime mortar is still white(ish), because the tar has not penetrated it. I wonder are you using hydraulic lime?<br />   Frank]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3251#Comment_3251</link>
		<guid isPermaLink="false">https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3251#Comment_3251</guid>
		<pubDate>Tue, 15 May 2007 22:55:41 +0100</pubDate>
		<author>Chris Wardle</author>
		<description>
			<![CDATA[I've got the same problem on a chimney, no longer in use.  Tried papering, stain block paint etc, always comes back through.  Just have to use stain blocker and re-decorate the area once a year.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3257#Comment_3257</link>
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		<pubDate>Wed, 16 May 2007 08:49:11 +0100</pubDate>
		<author>Gervase Webb</author>
		<description>
			<![CDATA[With manure, it needs to be as fresh as possible - the best place to get it is from the floor of a milking parlour first thing in the morning, as it's dead fresh, easy to shovel up and not contaminated by loads of straw and feed.<br />Dilute it to the consistency of melted ice-cream in a bucket or trug and whip it up with a paddle mixer, then paint two coats on to the sooty surface, rubbing it well in and allowing it to dry thoroughly  between coats. Then mix in manure to the scratch coat in a ratio of 3:9:1 lime:sand:manure, working the surface and trowelling up any cracks with a wooden float as they appear. Scratch a key when it's green hard and plaster second coat and lime skim as normal. I've not known that method fail, and have used it over walls that were oozing tar.<br />It's the technique that was used for parging chimney linings in the UK for hundreds of years, and is still used on flues in developing countries.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3311#Comment_3311</link>
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		<pubDate>Fri, 18 May 2007 17:30:41 +0100</pubDate>
		<author>chuckey</author>
		<description>
			<![CDATA[Wonderful solution (groan), do you know how it works? I wonder if I can get my brothers-in-law to start a business with me, selling "farm fresh flue seal" in plastic tubs.<br />   Frank]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3316#Comment_3316</link>
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		<pubDate>Fri, 18 May 2007 22:32:48 +0100</pubDate>
		<author>Gervase Webb</author>
		<description>
			<![CDATA[Dunno how it works - I'm told it's summat to do with the mucous in fresh cow dung - but it does work. And there probably is a roaring trade to be made - if people buy ready-made vanilla limewash I'm sure they'll pay good money for cow crap!]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3436#Comment_3436</link>
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		<pubDate>Thu, 24 May 2007 20:20:49 +0100</pubDate>
		<author>suibhne</author>
		<description>
			<![CDATA[Gervase, I like your idea. Ive just opened up an old fireplace and am going to move my solid fuel rayburn back into it, after I plaster the lower half which is visible. I was wondering if this mixture of fresh cow manure would help prevent cracking of the plastering directly behind the rayburn which is probably going to get excessively hot ?<br /><br />I live beside a dairy farmer so procuring the manure wont be a problem, just a little awkward to ask :)<br /><br />Thanks !]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3439#Comment_3439</link>
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		<pubDate>Fri, 25 May 2007 07:59:28 +0100</pubDate>
		<author>tony</author>
		<description>
			<![CDATA[Lime plaster will do the job with no dung. Before the days of admixtures cow dung was commonly used as a workability agent.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3441#Comment_3441</link>
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		<pubDate>Fri, 25 May 2007 10:01:37 +0100</pubDate>
		<author>Rachel</author>
		<description>
			<![CDATA[We have found that just lime plaster without the dung doesn't always do the job if there's a possibility of soot coming through. Dung also does a good job of crack prevention.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3444#Comment_3444</link>
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		<pubDate>Fri, 25 May 2007 13:32:13 +0100</pubDate>
		<author>tony</author>
		<description>
			<![CDATA[My  comment was for Suibhne and about the heatproof and anti cracking properties of lime render.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3445#Comment_3445</link>
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		<pubDate>Fri, 25 May 2007 14:53:43 +0100</pubDate>
		<author>funcrusher</author>
		<description>
			<![CDATA[EASY. I  use 'knotting', just painted over the plaster, and it works perfectly. That is not surprising, because knotting is designed as a barrier to prevent the sticky sap in knots from staining paint - and the sticky sap usually contains natural turpentine, which is what creates the tar in your chimney! Knotting is I think a form of shellac, made i think from a natural gum of a tropical tree?<br /><br />The solvent is meths by the way, and a little knotting goes a long way so not as expensive as it first seems. You can buy it at any DIY store. If you want a lot, go to a commercial decorators merchant.<br /><br />It is extremely easy to use - but don't spill any because it will be diffuclt to remove once dry.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3448#Comment_3448</link>
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		<pubDate>Fri, 25 May 2007 19:22:49 +0100</pubDate>
		<author>Gervase Webb</author>
		<description>
			<![CDATA[The problem with a shellac or varnish - or any of the modern polymer barrier paints -  is that the plaster is no longer breathable or flexible, and the surface won't take limewash or water-bound distempers.<br />As for cracking, any lime plaster will withstand the heat of a nearby stove provided it has a chance to carbonate fully and dry out before the heat hits it. The dung does make it more flexible, however, and is the best way to stop soot and tar leaching.]]>
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		<title>soot/tar coming through lime plaster</title>
		<link>https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=288&amp;Focus=3452#Comment_3452</link>
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		<pubDate>Sat, 26 May 2007 14:52:14 +0100</pubDate>
		<author>suibhne</author>
		<description>
			<![CDATA[Excellent, thanks a lot for your opinions. Seems lime plaster on its own should be good enough for the job I need.]]>
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