damp plaster

geordief

2 questions really.

I have a chimney stack with 4 flues 2 of which are completely blocked (one with a lead cap (just bent over and stuck in place with silicon mastic) and the other with cement).

In addition these capped flues do not have any vent at the base where the fireplaces presumably used to be in the house.

This was done before my time , by a professional roofer , but I am wondering whether I should be unblocking them (and capping them correctly)
.
The caps have been in place for 25 years and I am wondering whether any moisture trapped in at the time may now be long evaporated (through the room walls if by no other way)

On the other hand , if there has been damage to the stack itself (which there has -and I fixed it last Winter) would that introduce more moisture that might benefit from the uncapping of the flues ?


The second question is this.

When plaster has been damp for a long period of time (but not especially damaged -it is firm and completely attached to the rendering behind) how long can it take to dry out if we assume that the source of the dampness has been fixed?

I ask because I have attempted to speed up this process by keeping a fire in the chimney behind the plaster lit for 7 days now and counting (prior to that I just left the plaster exposed for 6 weeks or so after I had fixed the source of dampness from the chimney stack behind)
.
When I feel the plaster with my hand it is warm (not hot but perhaps 3 or 4 degrees above body temperature) continuously but it is not really drying out completely.It will probably take paint but I am reluctant to start because I assume it must be possible to dry it out entirely first by this means .

So is it possible for very old plaster to be extremely slow to dry completely (even with a source of heat behind it from a lighted chimney for 7 days and nights at a stretch)? - or is it more likely that the rendering behind the damp parts are holding the moisture and causing the endless drying period?

BryanF

geordief wrote: »

2 questions really.

I have a chimney stack with 4 flues 2 of which are completely blocked (one with a lead cap (just bent over and stuck in place with silicon mastic) and the other with cement).

In addition these capped flues do not have any vent at the base where the fireplaces presumably used to be in the house.

This was done before my time , by a professional roofer , but I am wondering whether I should be unblocking them (and capping them correctly)
.
The caps have been in place for 25 years and I am wondering whether any moisture trapped in at the time may now be long evaporated (through the room walls if by no other way)

On the other hand , if there has been damage to the stack itself (which there has -and I fixed it last Winter) would that introduce more moisture that might benefit from the uncapping of the flues ?

you need to get up on the roof/attic and inspect the chimneys/roof. there are moisture meters on th emarket that might help you find the route of the problem..

geordief wrote: »

The second question is this.

When plaster has been damp for a long period of time (but not especially damaged -it is firm and completely attached to the rendering behind) how long can it take to dry out if we assume that the source of the dampness has been fixed?

I ask because I have attempted to speed up this process by keeping a fire in the chimney behind the plaster lit for 7 days now and counting (prior to that I just left the plaster exposed for 6 weeks or so after I had fixed the source of dampness from the chimney stack behind)
.
When I feel the plaster with my hand it is warm (not hot but perhaps 3 or 4 degrees above body temperature) continuously but it is not really drying out completely.It will probably take paint but I am reluctant to start because I assume it must be possible to dry it out entirely first by this means .

So is it possible for very old plaster to be extremely slow to dry completely (even with a source of heat behind it from a lighted chimney for 7 days and nights at a stretch)? - or is it more likely that the rendering behind the damp parts are holding the moisture and causing the endless drying period?

sounds like you need to solve question A before solving question B

geordief

BryanF wrote: »

you need to get up on the roof/attic and inspect the chimneys/roof. there are moisture meters on th emarket that might help you find the route of the problem..

sounds like you need to solve question A before solving question B

(thanks for reading my post.I know it was long winded.)

I did all that last winter.I chased out the (large) cracks in the rendering , especially around the actual pots.I filled them in with Tetrion All Purpose Filler
after which I gave 2 coats or Masonry Paint.

This stabilized the problem but since it wasn't clearing up completely I decided to scrape off all the (indoors) paint -about 2 months ago , a lot of which was Damp Seal .

This showed considerable dampness in the plaster itself all over the wall (I do have a moisture meter) but within a few weeks nearly all the plaster had dried out perfectly acceptably.

However there are areas in the wall (the exposed plaster) that are resisting this dry out and so I decided to back warm theses areas with a continuous fire in the chimney (168 hours of continuous warmth that transmits right through into the room at about 40 degrees I guess)
But even this is painfully slow and that I why I am wondering if the moisture can actually get locked into the plaster even when the source of the moisture has gone.
Because if that can't happen I am at a bit of a dead end.

I could just repaint the room as I am confident the brown stains won't reappear but I really want to hold off until the dampness has gone entirely.

Going up to the attic is a job I don't enjoy as it is so cramped .I have done it though many times over the years and the last time I did find dampness below 3 or 4 feet below where the chimney stack meets the roof but not directly beneath the roof.

I guessed that might be residual from before I did the job on the chimney stack last Winter and that it might be soaking up from below .

If that is the case then the drying time could be years (that mightn't bother me if I was confident that the source of the water ingress was solved , that the room could be decorated and that the locked in dampness would gradually evaporate away in time )

I also checked the timbers of course with the moisture meter and they were bone dry.

BryanF

it sounds like you have a good grasp of the basics covered. it might be time to employ a specialist..

1. what year was the house built?
2. ie was a cavity tray installed in the chimney?
3. is it an old stone & lime wall/chimney?
4. is there a chance there is water migrating from elsewhere and only noticeable at the chimney?
5. is there any other damp/mould/condensation problems in the house?

niallb

Any chance you have a kerosene boiler venting into the stack ?

geordief

It is an old house (around 1800 and with very thick stone walls) and since I am guessing a cavity tray is something similar to a damp course I doubt there is anything like that.

There wouldn't be a damp course in the house at all but that wouldn't have a bearing on this as I am talking about an upstairs room.

I think you could be right about it being an old stone & lime wall/chimney as I have been told that there is also some added ingredient , perhaps turf -or ,God forbid animal manure that leaches through when it gets damp.

4)is there a chance there is water migrating from elsewhere and only noticeable at the chimney? I don't think so .There is a flat roof at one end but I have been up under it in bad weather and have never noticed any kind of a leak.Also that whole area is the highest part of the house..
..
5)yes terrible mould and dampness that I can't address since it is an old house and I don't have the money to heat it properly in the winter or even keep out the damp when we get humid weather (sometimes!) follwing on a cold spell- but this particular room is South facing ,upstairs and doesn't suffer really from mould (just mildew on the curtain linings that spreads from cold radiators I think)

No, niallb no kerosene boiler in that stack.Do they cause dampness ? We do have a stovethat uses another stack and after last winter there was a stain but it is the first I ever noticed (I did a job on that stack since and that stain is also taking a while to dry although it is far less serious maybe on account of the continuous use of the stove providing warmth)

heinbloed

As BryanF already said: it might be the time to get the specialist in.
You have a building from 1800 something. The chimneys propably of the same age. These are capped.

Sticking out into the cold they are cold at the top, with a temperature similar to the outside temperature - theoretically.
Naturally they take up water, ingressing rain,fog. Naturally a damp surface is colder than a dry surface, the internal material temperature of the chimneys (outside, the visible part above the roof) is therefore considerable colder than the air temperature outside. Evaporation of the contained moisture cools surfaces....

So you have a condensor.

This condensor will - similar to a heat pipe - produce water, condensate. Running down in your chimneys. Even if the chimneys are perfectly water tight condensation will occure. Esp. in Irish winter time.

Demolish them after getting permission. Reduce the height of the chimneys down to the heated space in the house. Fill the remaining chimneys, use them as a radiatior (see: thermal activation of structural elements,google).

geordief

heinbloed wrote: »

This condensor will - similar to a heat pipe - produce water, condensate. Running down in your chimneys. Even if the chimneys are perfectly water tight condensation will occure. Esp. in Irish winter time.

Demolish them after getting permission. Reduce the height of the chimneys down to the heated space in the house. Fill the remaining chimneys, use them as a radiatior (see: thermal activation of structural elements,google).

I couldn't see much immediately when I googled that term (you don't have an URL do you?) but I think I get the point.
Don't you think that you would get a similar result if you just filled in the redundant flues -and didn't bother about the demolition.
And if you filled them , would sand do the job (cement seems so final)?

heinbloed

Here the wiki explanation of the heat pipe:

http://en.wikipedia.org/wiki/Heat_pipe

Here a picture of a heat pipe in an evacuated tube used for solar thermal aplications:

http://ejaisolar.com/solar_collector_heat_pipe.asp

The closed copper tube is your chimney.Instead of having an organic solvent as a thermal carrier water will do the same job. It condenses at the coldest point and runs down again. Evaporates again because of the warm house, rises up to the coldest point where it condenses again.
Like fog in the cold grass, morning dew.
The cold impact, the 'transport of coldness' will stay, the chimney needs to be opened or demolished. Or heated so no condensation occures.
We see the same problem with condensing boilers connected to unsuitable chimneys, chimneys which are made fom porous materials.