Rising damp in perimeter wall

[Anonymous]

Hi all

I have a suspected rising damp problem on the interior face of a perimeter wall, on a listed 17th C property. The wall is plastered internally with hydrated lime plaster and is showing dark patches near the junction with the interior floor. The interior floor is new and solid with a membrane. There are also damp patches which appear to be a result of water penetrating through the solid 9 inch wall. The property has no guttering.

The mineral breathable paints I have looked at require a maximum surface wetness of 18% and the damp patches are wetter than that. I am therefore unable presently to paint.

The advice I have received so far is to paint the wall with porous "cellar paint". This only comes in white and I suspect it would still show the darker damp patches from behind. White would also not fit in with the proposed colour scheme of the room.

Other advice I have read is to fit guttering and improve drainage around the base of the walls externally by making a run-off chamber (more efficient than a French Drain which can block). Also I can excavate a few inches around the base of the interior wall inside the property and ventilate it within the room but this will disrupt the solid interior floor and could potentially look awful with floor grilles. Is it possible that these measures will reduce the surface wetness to less than 18% so it can be painted?

Another possible option is the insertion of a slate or chemical DPC. Is this generally allowed by local councils on old listed buildings?

Thanks
Rob

 

[Anonymous]

A new, solid (concrete?) floor with a membrane....

 

[Anonymous]

A York stone floor with underfloor heating. The floor is unbreathable - solid concrete and insulation with a thick membrane. The damp problem has not worsened since the floor was laid.

 

[Anonymous]

It's very likely the damp isn't 'rising'. Chemical injection - keep your money.

Concrete flooring with a membrane wouldn't be my first choice, but as you have it now then you have to think around it.

How long ago was this laid? It can take concrete a very long time to dry - gallons upon gallons of water in there - and with a membrane it's only really able to go out and into your walls possibly. Some damp could be condensation.

What are your walls built from? What sort of render/pointing have they got?

 

[Anonymous]

hi, thanks for your message.

The floor slab is dry - tested with a damp meter. The wall is old brick with lime mortar and plastered internally in lime. Hydrated lime from a builders' merchant may have been used.

 

[Anonymous]

Well, damp meters aren't the most reliable method, although often it's an opposite problem with yours of damp reading when there is not a problem, and damp may still appear around the edges of a non-breathable floor.

Is the pointing sound? There may be gaps which are allowing ingress of moisture.

 

[Anonymous]

I would look outside for the problem. Could be splashback from the ground. I would certainly consider gutters. Mike.

 

[Anonymous]

How do the ground levels compare inside and out?

what did the new floor replace ?

 

[Anonymous]

As Mike says, the first thing I would do is fit guttering. The amount of whater running of a roof in heavy rain is astonishing, and if this is soaking into the ground right beside the house, it's bound to be at least partly responsible for the damp.
Curing damp is usually a step-by-step process. You do something, then you wait and see what effect it's had. If you don't want that wait to be too long, thenyou really need to hack off the lime plaster from inside the wall up to well above the damp line, in order to allow the wall to dry out properly. If you leave it in place, drying out could be a very slow process.

 

[Anonymous]

Hi there

Thanks to everyone for their responses! <IMG SRC="http://www.periodproperty.co.uk/discussing/smileys/smile.gif" BORDER=0 ALT="">

I think I am getting closer to finding one of the causes of the problem. I have removed a small section of the plaster and can see two coats - a thick scratch coat underneath and a thin finish coat on top (about 2mm).

When I dip the scratch coat in water it soaks it up like a sponge. However a drop applied to the finish coat sits on it without being absorbed.

The surface of the top coat is hard, white and shiny.
I seem to recall their using playpit sand and lime but it looks increasingly like they added something else - cement possibly?

Does anyone know where I can get it tested to see if it contains any cement please?

Thanks
Rob

 

[Anonymous]

Mostly the huge intelligence of craftsman helps them not to forget to give a shovel cement in any render and mortar. Scratch with your car key or any other metallic tool, if it is hard to get a hole in the render, it is cementous 'improved'. Maybe there are reactions between cement and sulfates in your wall which cause swelling and very hygroscopic water sucking salts, maybe the salts are 'only' nitrates, which will suck water too.

I recommend to tear off the damp mortars and giving a new pure hydratic lime render on it to adsorb the salts. Maybe this procedure must be done twice, but perhaps? The main thing is to get the salts out (if it is salt and not a leaky gutter).

Rising damp it will never be, because there is no capillary transport between the fine pored stones and the rough pored mortars.

An additional remark: Please do not trust in 'mineral' coatings, if they have dispersed synthetics in it as many water glass based paints from wellknown producers - in spite they are named 'mineral'. It is just a fake they developed for very intelligent conservators. It would be better to smear excrements on the wall.

Reason: The 'breathing' of coatings does not bother, because 1000:1 of water transports in walls are in fluid form and will be stopped by any sort of dispersive synthetic coating. So if you will certainly moisture up your wall, take such paints.

To get rid with damp problems, try the link.

Good luck

Konrad



Damp walls - a Guide

 

[Anonymous]

This thread needs further exploration... Gutter or no gutter, what surrounds the house - earth, gravel, paving...? And is the ground level outside even remotely higher than the floor level inside? Are the external walls covered in render? If so, the moisture is trapped between plaster inside and render outside, and has no way out but up. Not sure about the 'it isn't coming from the ground' argument.

We faced a similar situation. Whatever moisture used to come up through the floor of the house has to find a new way out because of the concrete floors. So it heads for the walls. If the ground surrounding the house allows, it'll evaporate out. WIthout gutters, this will take longer because the ground will be waterlogged, in which case you may find some in making its way inside. If your inside floor level is lower than the outside ground level, however, nothing you do will stop the damp, unlesss you even the playing field by lowering the outside ground level, or digging a small ditch to inside floor level around the house and filling it with gravel, for instance... earth contains moisture, full stop. Obviously, don't do anything that might structurally effect your house without professional advice... <IMG SRC="http://www.periodproperty.co.uk/discussing/smileys/smile.gif" BORDER=0 ALT="">