Plastering over damp walls.

[whoisthedaddy]

Hi all,

I am renovating an old Victorian end terrace house which has been suffering from a little damp.

I have just removed most of the existing plaster as it was damp and almost falling off the walls.

A damp specialist is injecting a chemical damp proof over the next week or so but the question remains as to whether I dot and dab or use battens. The plasterer I use says that dot and dab will be fine but I have my doubts given the previous history of dampness. (3 of the walls are external - the front/back and side). I am worried about damp coming through the dot and dabs and penetrating the plasterboard.

I have a couple of questions:
1. Presumably the walls could also be plastered over brick with no plasterboard at all?
2. Is it possible to dot and dab insulated boards - I suspect the answer to this is no! if so are these the ones that are 4 times or so more expensive and you have to batten them as well - yikes?
3. Are there any shortcuts or tips for fixing wooden battens. I seem to remember somewhere that there are special nail in fixings that can be used which will speed up the process? What size should the battens be and what is the best way of padding them out?

Thanks
Lee.

 

[Richard C]

A damp specialist is injecting a chemical damp proof over the next week or so but the question remains as to whether I dot and dab or use battens. The plasterer I use says that dot and dab will be fine but I have my doubts given the previous history of dampness. (3 of the walls are external - the front/back and side). I am worried about damp coming through the dot and dabs and penetrating the plasterboard.

You should not D&D standard wall board on external solid brick walls as the adhesive dots will cause cold spots which can lead to condensation. There must be no further damp ingress (presumably why you’re having the damp treatment) or it will show through, are they injecting a damp proof course or treating the walls externally?

1. Presumably the walls could also be plastered over brick with no plasterboard at all?

Yes you can but older houses originally used a breathable lime render. You can use a waterproof render mix or a specialist base plaster such as Dry-Coat but there must be no sign of damp remaining in the wall. Make sure your plasterer knows what he’s doing!

2. Is it possible to dot and dab insulated boards - I suspect the answer to this is no! if so are these the ones that are 4 times or so more expensive and you have to batten them as well - yikes?

You can D&D insulation board but you must also use nailable plugs or through fixings to mechanically secure the boards to the wall; you can also batten. Damp can be expensive to eradicate but cost is relative!

You should also be aware that if you’ve removed more than 24% of the plaster from external walls, Building Regs. Require you upgrade insulation to current standards so, strictly speaking, you should be upgrading the insulation anyway. If not, be careful you don’t get caught out & this can happen if you’re having BI inspections of other controlled building work.

3. Are there any shortcuts or tips for fixing wooden battens. I seem to remember somewhere that there are special nail in fixings that can be used which will speed up the process? What size should the battens be and what is the best way of padding them out?

Generally shortcuts = bodge = unreliability. I would not advise nails for fixing battens, bashing old brickwork with a hammer can cause an awful lot of damage loosening the mortar joints & even damage the bricks themselves. If you have a decent hammer drill, battens are not difficult to fix with screws/plugs, use packers to keep them level.

 

[whoisthedaddy]

Richard,

Many thanks for taking the time to reply.

There were a number of reasons for the damp but mainly a lack of damp proof course, lack of ventilation, blocked up fireplaces with no vents (and full of soot!). I am confident that once the chemical damp proof course has been installed with air vents, chimney ventilation etc. all will be dry!

I think I am going to go with the waterproof cement based plaster solution for a number of reasons but mainly because it seems easier and quicker and therefore cheaper than wooden battens!

A couple of other forums have some interesting feedback on Izonil waterproof and breathable plaster but need to check the cost with Buildbase tomorrow and compare this to DriCoat. (I have no experience of either so will ask around and speak to my plasterer). My plasterer is really good so I have no worries at all there.

With regard to issue of removing over 24% of plaster from external walls I fear I may already have removed this amount - Doh!.

I am using Building Control (putting lintel in supporting wall) but using a private company (jhai) as they were cheaper and more reactive that the council. My impression is that they are less stringent but time will tell - either way I'll keep the inspector away from the rear walls anyway! Thanks for the heads up....

Thanks for the advice.
Regards
Lee.

 

[northernwarrior]

Normally the DPC company would provide a specification for you to follow, otherwise they may claim invalidation of guarantee if the dpc fails, but as rich c said it's usually followed up with a sand cement spec (loads of contention re this) or breathable lightweight plaster like limelite ,dri coat, izonil (normally double the cost of others) i am an approved contractor for the following company, give em a shout
http://www.sovchem.co.uk/category-name/plasterers-renders.html

 

[Richard C]

I think I am going to go with the waterproof cement based plaster solution for a number of reasons but mainly because it seems easier and quicker and therefore cheaper than wooden battens!

I would agree with going for a plaster/render solution but I don’t agree it would be cheaper than batens & boards, it won't.

A couple of other forums have some interesting feedback on Izonil waterproof and breathable plaster but need to check the cost with Buildbase tomorrow and compare this to DriCoat. (I have no experience of either so will ask around and speak to my plasterer).

Traitor ; there are others on here with far more experience than I regarding damp renders/plasters, hopefully they can also advise.

My plasterer is really good so I have no worries at all there.

I hope your right but if he suggested D&D plasterboard onto an external solid wall, I’d be concerned; there is far more to plastering than getting a good skim finish!

With regard to issue of removing over 24% of plaster from external walls I fear I may already have removed this amount - Doh!. I am using Building Control (putting lintel in supporting wall) but using a private company (jhai) as they were cheaper and more reactive that the council. My impression is that they are less stringent but time will tell - either way I'll keep the inspector away from the rear walls anyway! Thanks for the heads up....

IMO it’s a stupid regulation but we all have to do our bit to save the planet . I think an independent BI is more inclined to “ be blind” but who knows; just be careful.

Also be mindful of northernwarrior advice regarding warranty of your new DPC!