Thermal XP board over lime plaster?

littlemiss19

Hi everyone,

We live in a Victorian terrace that has a few damp issues and are having a bit of a mare with our damp specialists. We asked them to provide damp-proof course around our fireplace in the dining room and in the pantry as the original plaster was flaking away. We commissioned a survey from an independent damp-proof specialist who recommended using lime plaster. We asked the damp specialists to use it and they agreed. 

Since the job has been completed we have two issues;

1. In the dining room the lime plaster top coat (skim?) is really rough like course sandpaper. 
2. The plaster in the pantry is blotchy. We waited 4 weeks and have put on a coat of Wickes' New plaster paint as an undercoat and it's really patchy. 

For the first issue, they have said they are not able to get the skim any smoother and don't normally work with lime (not mentioned when they agreed to take the job on). They offered to try another lime skim coat but could not guarantee it will be any smoother. They have suggested we pay for thermal boarding and then a multi-finish skim on top of the boarding. They are looking to charge us another £700 for this. Obviously, we are not happy to have to pay extra for their incompetence/lack of communication. We are not experts and are wondering if this is a suitable and effective type of damp-proof course.

For the second issue, they informed us that they used lime backing and then gypsum multi-finish skim. Which I understand could be an issue as they react to each other. However, I think that as we have attempted to paint over it, we may not be in a position to get them to redo the plastering. 

We have yet to pay them in full having only paid a 30% deposit. 

Any thoughts on either issue would be appreciated. 

Thanks,
Little miss

FreeBear

littlemiss19 said:

Hi everyone,

We live in a Victorian terrace that has a few damp issues and are having a bit of a mare with our damp specialists. We asked them to provide damp-proof course around our fireplace in the dining room and in the pantry as the original plaster was flaking away. We commissioned a survey from an independent damp-proof specialist who recommended using lime plaster. We asked the damp specialists to use it and they agreed. 

Since the job has been completed we have two issues;

1. In the dining room the lime plaster top coat (skim?) is really rough like course sandpaper. 
2. The plaster in the pantry is blotchy. We waited 4 weeks and have put on a coat of Wickes' New plaster paint as an undercoat and it's really patchy. 

For the first issue, they have said they are not able to get the skim any smoother and don't normally work with lime (not mentioned when they agreed to take the job on). They offered to try another lime skim coat but could not guarantee it will be any smoother. They have suggested we pay for thermal boarding and then a multi-finish skim on top of the boarding. They are looking to charge us another £700 for this. Obviously, we are not happy to have to pay extra for their incompetence/lack of communication. We are not experts and are wondering if this is a suitable and effective type of damp-proof course.

For the second issue, they informed us that they used lime backing and then gypsum multi-finish skim. Which I understand could be an issue as they react to each other. However, I think that as we have attempted to paint over it, we may not be in a position to get them to redo the plastering. 

We have yet to pay them in full having only paid a 30% deposit. 

Any thoughts on either issue would be appreciated. 

Thanks,
Little miss

Presumably this was a chemical injected DPC ?

Did they then slap the usual waterproof render on the wall to a height of 1-1.2m before plastering ?

I have done a bit of lime plastering, and it really isn't that difficult to get a smooth finish. The key is to use the right mix for the final coat - I use a mix of one part lime putty to two parts fine marble powder and apply less than 1mm thick. Get the right mix, and you can get a polished finish.

Putting gypsum over the top of lime is frowned upon by purists - It can be done, but only after the lime is fully hardened and dry. If you do it too soon, the gypsum skim will crack.

As for overboarding with XPS or Celotex type insulated plasterboard - You need to know if the work done has cured the damp. If there is still damp in the wall, it will be trapped by the insulated PB and quietly do damage to the wall unseen. If you were going to insulate this wall, I would have suggested cork or woodfibre boards with a (pure) lime skim.

ChasingtheWelshdream

FreeBear said:

As for overboarding with XPS or Celotex type insulated plasterboard - You need to know if the work done has cured the damp. If there is still damp in the wall, it will be trapped by the insulated PB and quietly do damage to the wall unseen. If you were going to insulate this wall, I would have suggested cork or woodfibre boards with a (pure) lime skim.

I second this, having done just this.

Waterproof render slapped onto a 'damp' wall by previous owners. A tide mark came through, I hacked off the plaster/render to find a brick-sized hole that had just been filled in with plaster, with cold air blasting through. There is no evidence of penetrating damp, but investigating further seemed that the hole was funnelling in cold air and concentrating it around the area, with condensation forming when cold. The 'damp' was just masked. I have now repaired the hole properly and watched it carefully over the last few weeks. Now I am satisfied the 'damp' is cured, I have decided it is safe to put insulation on (finished yesterday!!).

I wouldn't have put the insulation on if the damp persisted, but have also repointed the other side of the wall in lime, so it can still breathe externally.