Conservatory walls drying out

[DavidJW]

I am having a new conservatory to replace a 20 year old softwood one which had gone rotten.

The walls and their foundations are new; but the base has been built up on top of the old concrete one with a 50mm polystyrene layer and plastic membrane. This was done about six weeks ago.

The photo at http://tinypic.com/view.php?pic=638kvmw is a close up of the wall showing the edge of the membrane.

What concerns me is the wavy white line and the dampness below it. The floor and the rest of the wall are completely dry. It is just the damp area running all round the bottom of the wall.

The conservatory suppliers say that this is perfectly normal. But I would be very unhappy if damp appeared after the walls have been plastered.

Do I have anything to worry about?

 

[noseall]

the first thing i noticed was the dpm has not been turned into the dpc joint.

i presume there is a dpc under that first course of blocks?

 

[noseall]

apart from the above, the efflorescent salt line IS perfectly normal.

 

[DavidJW]

I asked the supplier if there is a dpc in the inner skin of the wall and was assured that there is.

I'm not worried about the efflorescent salt line - that will get covered by the plaster. It is the dampness underneath that line, which does not appear to be drying out, which concerns me. Is it just a case of this will take a very long time to dry or could it indicate a fault in construction?

Presumably if there was no dpc the dampness would have risen up further considering the rain we have had and the wet ground.

 

[noseall]

Presumably if there was no dpc the dampness would have risen up further considering the rain we have had and the wet ground.

not necessarily no. if water has been ponding against the blockwork, then the dpc would be irrelevant.

is it a cavity wall construction?

 

[DavidJW]

if water has been ponding against the blockwork, then the dpc would be irrelevant.

is it a cavity wall construction?

Yes is is cavity wall the cavity is filled with fibreglass batts.

Please explain what you mean by 'ponding'.

 

[noseall]

Please explain what you mean by 'ponding'.

i assumed the 'connie' base would have been exposed to the weather, prior to the plastic sides and roof being fitted?

this would allow a certain amount of rain water to get trapped, creating ponding within the walls and floor and would result in the tide marks in your picture.

maybe?

 

[DavidJW]

You are quite right! It did rain quite heavily in the week between doing the base and putting up the walls and roof. The top of the wall was protected, so no rain could get down into the cavity. The dampness must just be the result of water laying on the base and splashing up. But why is it taking so long to dry out - five weeks

 

[noseall]

there could be a little water tapped in the cavity trough.

if the walls have been built correctly then there will be a space of some 225mm deep within the cavity and below the dpc. this space or trough has been known to fill with water, although it should not wick up into the blockwork if the dpc has been installed correctly.

 

[DavidJW]

although it should not wick up into the blockwork if the dpc has been installed correctly.

That's what I thought.

What would you do in this situation? The plasterer is supposed to start tomorrow!