On 2 Sep, 11:38, Mike wrote:
Hi
Long story but i'll try to not to go on for ever!. We had a 'pro' in
who injected DPC and re - plastered bottom metre or so of our ground
floor to solve rising damp. 6 months on we still have some damp and
have now given up on trying to get hold of the guy that did the work.
This is our first house and we simply cannot afford to pay anyone else
so need a DIY fix.
To be fair the job is not an entire disaster as it has worked in areas
where cement / sand undercoat was used. We opened up a chimney breast
before dampwork was done (to about 6 feet for a cooker) and for some
reason the guy has used plasterboard in this area plus in one other
small area of wall. We now appear to have penetrating damp in these
plasterboarded areas. you can clearly see damp circles where the dabs
are holding the plasterboard to the wall which get noticably worse on
wet days and salt crystals have formed on the surface of these
patches.
My guess is that the DPC is fine and the plasterboard is 100% the
problem (i know chimney breasts are problem areas but the other area
of plasterborded normal wall has the same problem and either side of
it is fine)
I'm guessing i need to rip out the plasterboard and re plaster as per
the rest of the house. Looking for a blow by blow run down of how to
do this, in particular how to treat / prime the brickwork, ratio of
mix for the undercoat and which damp proofing additives to use in the
mix (also not sure if i need to use additives in the skim coat?
Thanks to anyone who got through that lot and any advice will be much
appreciated.

The sand cement render would contain a proprietory damp/waterproofer
and form a containment barrier. As long as this containment also
crosses the chemical dpc it "works"
Exactly why the numpty didn't use the same technique in the problem
areas is beyond me.
Your idea is exactly right as to the way to deal with the problem. It
is possible that the new dpc is now exacerbating the original problem
as the damp is now rising in a concentrated area.
Regarding the preparation, chip away any old render or plaster as this
will wick the moisture upwards past the dpc if left in place. (I
assume he "did" put a dpc in the problem area???)
It should be perfectly fine to get adhesion to freshly chipped
surfaces without using pva or other adhesives. Sand and cement form a
perfectly good adhesion to brickwork as you can see by a properly
built brick wall! Don't forget to use waterproofer in the render mix.
If there is a problem with getting a starting adhesion "spatter" the
wall with mortar and let it dry (and stick) then use this as a key for
your render coat.