DIY Doctor UK DIY Forums

Hello, just wondered if anyone could offer any advice as I'm in a bit of a fix!

I temporarily moved out of my house just after Christmas as it had secondary flooding - there was loads of rising damp all over downstairs & it was off the scale when they tested with damp meters. The house is a mid terrace built in 1896.

The downstairs of the house was gutted, floors up, kitchen out, all plaster stripped to halfway up the walls & dryers & dehumidifiers were in for 3 months. A DPC was then injected into the mortar between the bricks. I then got a drying out certificate & work was started to reinstate everything.

The house has been replastered (with a concrete render under the plaster, not plaster board) & the plaster has now been painted. About 2 months after the plastering was done a few damp patches have appeared just above the skirting boards, all in the same places as before. A couple of the patches look like dark water marks & are damp to the touch. The other patch has bubbled the plaster. I've been told not to worry, that's it's normal & is the salts coming out the brick & the remaining damp drying. I am worried though, as no-one seems to be able to tell me conclusively it's not rising damp again, & surely if I've had a drying out certificate the walls should have been dry, so nothing should be coming through the plaster at this stage, unless it's rising damp again?

I just wondered if anyone could tell me if this is normal as I have no idea about these things!

Thanks for reading!

yes it is normal for patching to occur it will disappear with time

Hi there. I hope i am able to help you.

First of all, who installed the dpc? & who carried out the replastering and what exactly did they use?

There are many reasons why a dpc may not appear to work but in this case im interested that neither the plasterer or dpc installer can answer your problems.

The render you talk about is interesting. Using a specific type of render and applying it correctly is key to a successful dpc treatmnt. Either a purpose mixed salt/water resistant renovation plaster system should be used or a sand/cement render comprising OPC, good quality loam free washed plaster sand, and salt inhibitor/water proofer. These render systems need to be applied in layers of specific thicknesses and should not cover the dpc intection holes. The purpose of this render is to prevent the migration of salts from within the wall to the surface. This type of render also means that the damp cannot easily migrate also.

So, your render may not be correct. If this is the case, salt may be passing through the render. Some of the salts you would expect to come accross are not visible and they are hygroscopic so they will hold moisture and cause damp stains. Also your render may have bridged the dpc, or even something on the walls in the adjoining properties.

The dpc may also not be installed in the correct location. (I am assuming the walls are solid 225mm brick and that a cream or gel type dpc has been used?) The dpc should not be compromised by ground levels either i.e. these should be at least 150mm below the dpc.

Finally what decorations have you applied on the wall? A non alkalie emulsion should be ok, but anything else may form a skin on the wall causing residual moisture to become trapped behind it.

oh, and one other thing, what tests were undertaken to be able to offer the drying certificate?

Thanks for taking the time to help.

The builders sub-contracted a company to do the dpc in April. Chemdry were the company responsible for the drying out equipment - they came every couple of weeks & took readings from the walls during the drying out process. In June it was within the normal range & was considered 'dry'. The builders then put on the render & plaster, but explained to us that they were using a damp inhibitor in the render - other than that, I don't have any further info at the moment. The plaster has been emulsioned.

I saw the injections sites before the floors were put back down, & it looked like they were in the right place.

I'm sorry I don't have all the right info to tell you at the moment. I'll find it all out though!

Thanks again!