skimming on to cement in basement

[ljn]

Context:
Basement of a grade II listed building with brick walls, built on chalk. There is not much damp.
The floor is breathable limecrete ( I have just done that).
No DPC in the walls.
So there is moisture in the floor, walls and air.

I have had structural steel joists and posts put in. The first meter from the ground I have clad the steel with water resistant board- the kind you can use in bathrooms, and with green plasterboard in the upper parts. What would you render the boards with?

The brick walls, external and party, are mostly rendered with cement. That's how I found them. They are skimmed in part with pink gypsum. In parts they are skimmed with a grey/cement coloured skim. Parts were clad with plasterboard others with and old fashioned MDF- the light cardboardy version that you can break with your hands. Behind them there are raw bricks.
I would replace the MDF with green plasterboard.

So the walls are a bit of a crazy patchwork.
Would it be appropriate to skim everything with lime? On top of boards, cement etc?

A lime specialist who has proposed hacking all the cement and rendering with lime, but that would be a big job I'd prefer not to tackle, and also quite destructive, as it would take the front off all the bricks.

Any tips before I ask the Building Control inspector/CO?

I know that in the other listed buildings in the area they have used a high tech damp-resistant render.

 

[Lime]

I have had structural steel joists and posts put in.

What did the CO say about the installation at the time?
My opinion of covering up steel in an attempt to stop rust is futile because condensation occurs on steel and the water needs to evaporate otherwise the rusting will become serious.

 

[ljn]

The steels have a coating to prevents rust. That is what the engineer/Building control specified.
Cladding the steels with plasterboard was a requirement to protect them from fire, so leaving them bare is not an option.
The steels are set in deep concrete foundation piers, so there might be less damp there than the rest of the floor which is a more breathable limecrete.

My question is what to put on the plasterboard.

In general, there isn't any "damp problem". Being built on a high piece of chalk and on the basement it is quite dry.
But however "dry" it tends to be, I'd prefer to use something that can cope with a bit of humidity, possibly letting any water content to evaporate.

 

[CHRIS]

I'd prefer to use something that can cope with a bit of humidity, possibly letting any water content to evaporate.

Why not try and use some green moisture resistant plaster board that you can use in a bathroom and then just tape and joint it and finish with some roll on plaster (http://www.lime.org.uk/paints_finishing/Roll-on_Plaster.asp) i used this on a plaster board wall in my kitchen and looks quite good as it has a bit of texture, I think for fire stopping on steel you may have to double up on the 12.5mm plaster board but I will find out.

 

[ljn]

Thanks chris.
I got the floor materials from lime.org (Through limecrete.co.uk who did the job).
I guess if you can roll the lime onto cement render, you can also skim with lime.

Pink "fireline" plasterboard would be the one for fire. The building inspector is happy with a single 12mm layer.
But that isn't water resistant, so at the base, to the hight of 1 m circa, I used the hardybacker, which should be both water resistant and fire resistant.

 

[CHRIS]

Why not prime the plaster board with DG27 from Mike Wye and the skim the whole lot in a lime plaster. Just scrim tape the joints and when done lime wash the lot.

I would remove as much cement render as possible but don't do any more damage than is really necessary as it will be a real headache.

 

[ljn]

I spoke to Mike Wye /Ty-Mawr. They supplied the materials for the limecrete floor and were very helpful. They suggested painting the surfaces with a primer and then skim with lime. But it is more of an aesthetic patch than a practical solution.

Another alternative is a product called Izonil: http://www.izonil.com/us/plaster.html