Damp either side of bay pre 1900 victorian terrace

Postby helmo » Thu Jan 22, 2009 10:06 pm

I have damp patches about 5 ft up from floor level on either side of bay on the ground floor( solid brick walls 3 corse, suspended wooden floors) chemical dpc done concrete that was covering airbrick out front has been broken up and removed. The guys that did the injecting hacked off original plaster half way up wall and replaced it with plaster board adhered to the bricks with dabs of plaster then reskimmed, only the dabs are still very visible as damp patches in the reskim. There is painted pebble dash on front of house that was down to floor level so I hacked off lower 3ft. still no drying. What should I do next painstakingly hack off all the dashing??? remove plasterboard?? any suggestions where it could be coming from gutters clear bay felt ok help please
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Postby stoneyboy » Fri Jan 23, 2009 6:41 pm

Fitting plasterboard as you have described is wrong, you will probably be getting a very wet floor at the base of the plasterboard. Suggest your first move is to remove the plasterboard and concrete render the inside wall up to about 4ft.
If anything you should be repainting the outside rendering to stop water penetration, certainly not hacking it off.
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Postby Inform Timber and Damp » Sun Jan 25, 2009 1:33 pm

I am not keen on using dot and dab where damp is or was a problem, as both the adhesive and the plasterboard are very moisture sensitive and dabs will act as cold spots. damp on bays mostly caused bt water ingress around the window, corner posts and junction witjh the wall. Sound pebble dash is a good water repeller is it sound. is window wood or plastic ? does the cill project wall to throw water off building, are ground levels high, does pavement fall towards builing allowing water to sit against building? need to check all thse. Is the timber floor well ventilated below, are joists ok cos if it was rising damp or penetrating damp at base of wall problem these would be affected

Once source found tthen 2 options, tank using a cementitious slurry, and replaster in renovating plaster i prefer limelight or dri coat but can be difficult to source. or i have used drylined pnelling, others may think this strange but Victorians often panelled under windows and used drylining lathe and plaster very effectively if only slight moisture mvt. Many of our modern plasters fail very quickly in the same situation- modern tech eh!
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Postby helmo » Sun Jan 25, 2009 1:39 pm

The painted pebble dashing looks to be in good order after doing a bit of research i made the assumption that moisture maybe trapped within the walls as the house is old and lime mortar was probably used, would the dashing that was added some 50 years ago not be restricting the walls from breathing??

I am not sure if it may be penetrating damp or if its just condensation also, what is the best way to tell? would the concrete mortar not just restrict breathing more so and what would be the benefit of this?? originally the only damp patches appeared above the rising damp level about 5 ft and the wall paper rippled now i am concerned that it is rising that high as the new plasterboard is on the lower half of the wall and where it is fixed by the dabs bridging it has not dried.

Once the damp is correctly diagnosed i would also like to insulate these outer walls internally what is the best way of doing this without affecting the breathing?

thanks for any advice
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Postby helmo » Sun Jan 25, 2009 5:56 pm

Thanks for your reply, Window is double glazed pvc surround, pebble dash looks to be sound as does cill, i have removed the concrete path that went around the bay as it was blocking an air brick (not sure if i have to replace it though as soil beneath would gravel surfice or would this allow too much rain water to attack the foundations??

Not sure what the term "tank" is Would it be best to use a lime render on interior wall and to what height? and when thats done do i plaster directly onto the render or is there a way of incorporating insulation of some sort

I have repointed and replaced a few bricks under the bay and discovered it to be only one brick thick is this normal as the rest of the house is 3.

Obviously I dont want to decorate until i am sure damp source is isolated how long will i have to for it to dry out ?
( the walls have always been very cold would this affect the drying)

Many thanks for your input
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Postby Inform Timber and Damp » Tue Jan 27, 2009 9:50 pm

Any solid wall will allow some moisture movement most renders will be cement bases and restrict this movement which has the affect of reducing this 'breathing' affect of older lime mortars. Cement renders tend to deflect most water away but any moisture within the wall will not escape externally and could be forced internally causing damage to internal plaster aand decs. it is therefore impt that that the internal plaster can cope with this level of moisture ( were it is minimal ) or that it is isolated from the underlying wall by the use of a tanking layer( waterproof ) which holds the moisteure within the structure) or alternatively deflects the moisture somewhere else. Each situ is different but if the moisture within the wall is slight and external defects are fixed often replastering internally with a cement based plaster or render is often adequate. The diff comes in recognising the level of moisture present. Dot and dab is a very poor method on even the slightest problem wall.

Since you want to insulate consider a drylining approach with celotex or similar. It is not really practical to consider insulation and breathing because they are largey opposites. Hope this gives a bit more help.
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Postby jim beadman » Thu Jan 29, 2009 3:01 pm

whenever you install a dpc it takes months for the wall to dry out, the adhesive used for the plaster board is soaking up the moisture and showing as damp patches, platerer should have used sbr in the adhesive mix or tanked the wall befor plastering. tanking is a waterproof slurry that will stop the moisture comming through the wall. see the DIY Doctor projects section on Tanking and contact Property Repair Systems for free advice
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Postby helmo » Mon Feb 02, 2009 8:30 pm

so if i tank the inner walls with waterproof cement slurry then make a frame, plasterboard it and replaster how will the wall dry out as it is then sealed on both sides? should i use foil backed plaster board?
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