Damp in porch help

[fraya]

I hope someone can help me. I've read the thread on damp but I'm still unsure of what to do about a damp problem we have
We have a porch on the front of the house which has damp on one of the walls. The porch walls are stone, I'm not sure if they have a cavity, and the sides are (sorry about this I didn't put them in) plastic double glazed with a hideous plastic front door. I'm guessing the rain runs down the window and around the sill, and as there no drip channel underneath it runs down onto the wall and through to the inside. My first idea is to run a bead of sealant along the underside of the sill to see if the water drops off it when it runs underneath. We will be hacking the plaster off the inside wall and then I'm unsure of what to do.
I will want to put tongue and groove panelling on that wall (to match the other side which hasn't got any damp) but am wary of covering up and hiding future problems. I there anything else I can do to stop the damp and should I be lime plastering, pink plastering, or leave the wall unplastered and just panel?
I hope the pictures help and thank you in advance.

 

[Matt Green]

First picture: ground levels.

The plaster is likely failing because the external ground levels are not (at least) 6" below floor level. What's the floor construction?

 

[fraya]

As far as we know the floor rests on joists above a concrete base. Theres is a concrete slab a couple of inches below the gravel outside as well

 

[kevmiles1]

It looks like the plaster is gypsum (from the small patch i can see). I would find where the window is leaking and stop that then hack of the gypsum and replaster with lime and then limewash or distemper this will allow the wall to breathe. If you do this it should stop but I wouldnt use any selants if you are going to use lime

 

[Schoolmarm]

It looks like the plaster is gypsum (from the small patch i can see). I would find where the window is leaking and stop that then hack of the gypsum and replaster with lime and then limewash or distemper this will allow the wall to breathe. If you do this it should stop but I wouldnt use any selants if you are going to use lime

This is the right thing to do, but only after the ground levels are sorted. As being pointed out by Matt.

 

[Lime]

From what is shown, there is no drip edge on the sills either.
Combined with the high ground level I'd expect the wall to be damp.

 

[fraya]

Thank you for your replies.
To lower the outside level would it be best to dig up the concrete slab and put in a French drain or could we use those metal builders drainage channels?

 

[Lime]

Any lowering of levels is better than none but the best would be a lowering of all the ground surrounding the property (where it is high) to at least 2 metres away from the brick.

 

[fraya]

looks like a fun afternoon with the Kango hammer awaits then!

Thanks for the reply.

 

[MdB]

Something that hasn't been mentioned is condensation. The porch looks like it is uninsulated and unheated so the inside surfaces will be cold. Warm moist air from the house will hit inside walls of the porch and you will get condensation which will lead to mould and damp.

Reducing outside ground levels and adding drip lines are a good idea but will make very little difference to condensation levels if this is the cause of the damp patches.

If you have an internal door then ventilation in the porch to the outside could be considered though it will of course make the porch colder.

 

[fraya]

The humidity is very high there in the morning (I have a small humidity meter in there) but as the day warms up it goes down to acceptable levels. We try to leave the internal door open as much as possible to warm the porch from the house. I had considered putting a small radiator out there in the hope of solving the damp but it would mean running the pipe under the floorboards across the threshold to get to the right hand wall.

 

[Lime]

Looks much more like damp in the wall than condensation to me.
I'd expect the corners under the window to be affected and for black mould everywhere.
also condensation doesn't normally make the paint and plaster "blow".