Ventilation Mould and Moisture

[markm]

Hi

I have been looking at the forum for some time. It has been a really good source of information. Unfortunately, I am not experienced enough to offer reliable advice, but I hope that that changes in the near future.

For the past 10 months I have been working on a rubble stone and brick weaver’s cottage. We do not know the exact age of the house, but it’s probably from around the mid 19th centaury. As always, there was more work to do then expected, and we have ended up gutting the place,

Were possible, the Portland cement has been taken off internally and externally and replaced with natural hydraulic lime. The external walls on the inside have been replastered in NHL, using the guidance on the http://www.limestuff.co.uk, advice sheet. The plastering work was finished a week ago and we have been trying to let things dry out naturally. The internal temperature of the house is around 10 degrees C, without the need to use the central heating. However, there does appear to be moisture on the walls.

The property has a roof covering of traditional clay pantiles. Judging by the felt, it was last re roofed in the 1960’s. I know that it has been cold and damp, but we are starting to get white mould on the old felt and roof rafters. We have had some work done on the roof, such as leading around chimneys and replacing damaged rafters, tiles and felt. In addition, the internal walls of the roof space have been repointed, so generally, with all the plastering and pointing, we have been using a lot of water. We have not put any insulation in the roof as yet.

I am starting to think that I may have sealed up the roof void too tight. With all the faults and gaps, there used to be quite a few drafts. Some of the vertical brick joints did not have any mortar in them and you could see day light, now I think that ventilation was the reason. At the moment I have a dehumidifier working away in the loft and it is collecting a lot of water.

I am anxious to make sure that the house breathes properly, including the loft. I was going to fit a positive pressure ventilation system ( http://www.twistfix.co.uk/products/anti-condensation/nuaire-drimaster-product.html ) , but there is no point in doing that when the unit is sited in a loft, which has a tendency to damp. The other option is a whole house ventilation system such as the MANI3000 .( http://www.manrose.co.uk/specifications/manivent.pdf ).

To my request for advise please:

Should I turn the heat up to aid the drying of the lime plaster?

What is the best way to achieve ventilation in a loft roofed with traditional pantiles? “Santoft” make tile vents for the modern pantile, but it does not look suitable. There is little air coming from eaves and the tiles rest directly on the walls.

Has anyone experience of the whole house ventilation system or positive pressure ventilation system?

Thanks in anticipation.

Mark M.

 

[tobydog]

Hi Mark and welcome to the forum. A common response here is that someone more experienced will come along in a moment, however, for what it's worth, here's my personal view.

I would see any artificial ventilation system as a last resort. If you have tried everything else possible and still can't sort out the moisture problems then maybe consider them. You've clearly done quite a bit of work to the house and you still have quite a bit to go, so at the moment I would think that your house is still not balanced in terms of how it breaths. You could well have produced far more water than any old house might be designed to handle in such a short space of time so it might take a little longer to address through a combination of heating, ventilation and the dehumidifier. You could be looking at next spring/summer especially with rubble/brick.

You also need to bear in mind the time of year. Now is not a good time to naturally dry out old houses unless of course it gets very cold whereby the air can get very dry and could draw moisture out of the house. Also, bear in mind that if you are using the dehumidifier alongside extra ventilation, then you might find that you are dehumidifying your garden and everything around you. These units need to work in an enclosed environment. If you have actually sealed up your roof completely then it's likely that the moisture you are collecting in the loft is actually moisture from the whole house. Loft spaces themselves normally have no reason to be damp and it's usually what's going on below and the condensation it causes that's the biggest culprit.

Whilst NHL sets quick quickly compared to putty, I wouldn't be in too much of a hurry to dry it out too quickly. Lime plaster / render needs time and, in a perfect world, a natural drying environment.

How you ventilate and subsequently insulate your loft will depend on whether you want a cold or warm space. A cold space is far easier to achieve and should just require the opening up and clearing of the eaves with the usual ceiling insulation. Photo's would certainly help. If your tiles are in good condition, you could also consider opening up the felt in places to allow air flow but I would work on the eaves first to see if this sorts it.

Last spring we removed the cement from our timber frame plinth walls and with a few weeks the back of the sofa went moldy. It is now fine and the room is in balance. The plinth isn't totally dry, and it never will be because it was never intended to be but the sofa is no longer moldy.

As is the case with this educational site, I stand to be corrected.

Good luck and Happy Christmas to you and all.

 

[DJH]

Lime of course doesn't 'dry out', it cures from carbon dioxide in the air so my advice would be to open the doors and windows and let it cure at it's own pace. If you introduce heat then warm air against a cold wet wall will result in condensation which in turn inhibits the cure especially during the winter months. During the summer months we used to hang damp sisal, or sacking against newly lime plastered surfaces to stop them from drying out rather than curing. My advise is to open the doors and windows and let the air in though not if it's freezing.

That's always worked for me.

Happy Christmas

 

[markm]

Thank you Tobydog and DJH for your sound advice.

The tiles are OK, but I would not risk cutting the roof felt, as the coverage on these Somerset Pantiles is quite poor, as the overlap is minimal. Despite there being no insulation, there is litte air coming from the eave. If the mould persists, I guess I could put in a weather slate (away from the gas flue!) and take a core drill to the end gable wall.

I will continue to leave the doors and windows open when working there and let the NHL dry naturally. May be in a couple of months the building will have reached a balence.

Thanks once again

Mark M.

 

[middi]

Hello and welcome.

As to the general condensation, this is totally normal if you have just done loads of plastering and the temp. is kept at about 10 degC. It will take quite a long time for all those buckets of water used for the plastering to evaporate. The more heat and ventilation used within the building the faster the drying process will be. In an ideal world plastering is best carried out during late spring if the building needs to be occupied whilst plastering is carried out.

As to ventilation within the loft. if you have the usual pantile system with one of those hardly breatheable black sarking membranes ( and no insulation), the best , quickest and less costly options is to heavily insulate all the area above the upper rooms (?) ceiling joists and generously ventilate the loft space to avoid condensation and water drips ( bear in mind to especially insulate any water pipes if in the loft area)

Good luck
Middi

 

[markm]

Thank you Middi

Yes you have guessed the right felt membrane. As soon as the mould is under control, I will get that insualtion in.

Fortunately, we are not living in the house and so opening all the windows is not a problem. Ideally, we would have had the plastering done at a better time of year, but we were more concerned about structural issues. The woodworm was quite bad and only the main roof rafters and some first floor joist were worth saving. The external part of the rear rubble wall was only held up by the windows!

Sorry if my replies are delayed, as they are going through a moderator.

Thanks once again and Merry Christmas to you all.

Mark M.

 

[Penners]

I echo what has been said above. Think about all the water that has been used to make your lime plaster: it only has one way to escape from the newly plastered walls and that's into the house. If you've sealed up the building, then the internal air is very quickly going to get saturated (particularly if it's quite cold).

You need to get air moving through the house. If you're prepared to spend money to heat the house a bit, in the knowledge that you MUST also ventilate it well, then so much the better. This will allow your plaster to dry out gently while it's hardening.

As for the roof space, you must ensure that this is well ventilated, not just during the drying out period but for always. If your rafters get condensation on them which cannot escape, they can begin to rot.

 

[markm]

Thank you all for your advice.

Have posted thanks before, but as a new member my posts are going via a moderator, who rightly have other things on their minds at this time of year.

Ventilation and a bit of gentle heat seems to be the key. As I have said in previous posts, fortunately we are not living there, there was too much work required. I will get the insulation in when the mould is under control, to create a "cold" loft. I will make a decision on forced ventilation when the natural balance of the building is achieved - probably in the spring.

Merry Christmas to you all.

Mark M

 

[MatthewC]

What is the best way to achieve ventilation in a loft roofed with traditional pantiles? “Santoft” make tile vents for the modern pantile, but it does not look suitable. There is little air coming from eaves and the tiles rest directly on the walls.

Hi Mark

If you have pantiles resting "directly on the walls", surely the curve of each pantile allows ventilation? You need to make sure that the gaps have not been plugged up by some well-intentioned person since it was done in the 60's. That should ventilate the loft space, then use a breathable insulation material on the ceiling joists (e.g. various versions of sheepswool are available, if you can afford it).

Matthew

 

[markm]

Thank you Matthew.

Things have been delayed a bit over the Christmas period. It will be much easier to work when the rain stops.

I have been looking at tile vents, does anyone know one that is particularly suitable for "pantiles" ?

Happy New Year to you all

Mark M.

 

[Feltwell]

Mark - I've no personal knowledge of them, but "lapvents" have come up in similar conversations on here in the past.

http://www.lapvent.co.uk/index.html

 

[markm]

Thank you Feltwell.

Those look very interesting.

Happy New Year

Mark M.