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I have large damp patches on the ground floor internal walls of a terraced house built around 1900. These extend to about six feet in height - and over the full width of the walls. I have had a damp technician attend. He said there did not seem to be a problem with rising damp. The damp meter indicated the bricks were dry but the old mortar in between was significantly damp. He said this was due to salts in the old mortar. I intend to treat the old mortar with salt stabiliser then apply two coats of SBR slurry. I then intend to dry line the wall on wooden battens then skim over this. Is this a sensible option to solve the problem ?

If you drill the wall and attach battens you could have damp bridging problems.
Try painting 3 coats of aquapruff ontop of the slurry,on the last coat throw coarse sand on the wall so when it dries the drywall adhesive will have more grip to the wall.

Thanks for the advice Welsh Brickie. I've looked at the Cementone Aquaprufe product which sounds good. I have taken on board your advice about the damp bridging problems with the battens. If I use Aquaprufe do you think it pointless to first coat the walls with SBR slurry as the 3 coats of Aquaprufe should sufficiently tank the walls. Also Sometimes I have noted damp patches coming through plaster where the dabs of drywall adhesive have been applied. Could you advise further please.

no use the slurry it will fill the deep holes and give the paint more grip.If its applied right you shouldnt have any problems,just take your time.

Thanks again. Are you aware of damp patches appearing through plasterboard where the plasterboard adhesive dabs have been applied. Is it due to the hygroscopic element of the adhesive drawing in moisture from the room? I've seen this in some cases and my next door neighbour is currently experiencing this in a job he is involved with.

you will get damp circles in the drying out period for about 3-7 days after aplication but if its still occuring then damp is the cause,its highly unlikely to occur in internal walls,its usually on external walls.

Have applied the Aquaprufe. Tried a number of different brushes and roller - these all quickly clogged up . Finally tried a cheap 4" paintbrush with polyester bristles which applied the aquaprufe very well. I'm due to put on the final third coat. Aquaprufe dries quickly and I'll have to be quick in applying some sharp sand to this in order to provide a key for the plasterboard adhesive. Hope the plasterboard sticks to the wall okay.