The damp patch on my hallway wall is back. Had it treated about four years ago by one of those companies that inject silicone or whatever it is into the brickwork. Cost about £600 at the time. Looked fine for a couple of years but it started showing through again last winter and now it’s worse than ever, brown stain spreading across the wall about a foot above the skirting.
Do I get the same company back and make them redo it, or is it worth getting an independent damp survey done first? Not sure whether the original treatment just failed or if there’s something else going on. The wall is the one that faces the front garden so it gets all the rain.
Also not sure what an independent survey costs. Anyone had one done recently? I know it’s how long is a piece of string but a rough figure would help.
Do not go back to the original company. They will diagnose rising damp again and sell you the same treatment. That is their business model.
Before you spend money on a survey, check the basics yourself. Is the ground level outside higher than the damp proof course? Has any soil or paving been piled up against the wall? Is the guttering above that wall in good shape or is rainwater running down the brickwork? Nine times out of ten what gets called rising damp is actually water getting in from outside due to something straightforward like that.
If you do want a survey, look for a chartered surveyor who is RICS registered and does not also sell damp treatments. Expect to pay around £250 to £350 for a standalone damp report on a small semi. The ones who offer free surveys are the ones who want to sell you injections.
Doris, I hate to be blunt but there is a very good chance you never had rising damp in the first place and the injection was a waste of £600. The damp proofing industry has been running this playbook for decades, they come out with a moisture meter, wave it at the wall, declare rising damp, and sell you a chemical DPC that you did not need. Most of what people call rising damp in houses of that era is condensation or a bridged DPC from raised external ground levels or render that has been taken below the damp course. If the patch is in the hallway I would bet money it is condensation related. Get a proper independent surveyor, not a damp company, to actually diagnose what is going on before you spend another penny on it.
@Frankie91 you might be right. The patch is on an external wall about a foot above the skirting, which is why the original company said rising damp. But it only comes back in winter so maybe condensation does make more sense? The hall has no radiator and no ventilation apart from the front door. Going to get someone independent out to look at it as Penny suggested. Not paying another £600 to be told the same thing.
@halfpenny_doris, the fact it only appears in winter is the giveaway that this is almost certainly not rising damp. Rising damp, to the extent it exists at all, does not take summers off.
Before you spend money on a surveyor, go outside and check two things. First, look at the ground level against the wall where the damp appears inside. If the soil or a path or a raised flower bed has built up above your damp proof course, that is your problem right there. The DPC on a house of your era is probably only a couple of courses above original ground level. Second, check the guttering directly above that section of wall. A leaking downpipe joint or an overflowing gutter will drive water into the brickwork and it will show up inside exactly where you are describing.
I had a very similar patch on the back wall of our kitchen about six years ago. Turned out to be a cracked hopper where the downpipe meets the gutter. £40 part from Screwfix and twenty minutes up a ladder. The wall dried out completely within a few weeks once the water stopped hitting it 
Quick update on this. Bought a hygrometer off Amazon for £8 like @greenwhistle_hants suggested. Stuck it on the hallway wall near the patch. Humidity is sitting at 72-74% most of the time, which from what I’ve read is well into condensation territory. So it looks like Frankie was probably right and I wasted £600 four years ago. Lovely. Going to try keeping the heating on low overnight and cracking a window, see if it shifts.
@halfpenny_doris, 72-74% is high but not catastrophically so. That is firmly in condensation territory rather than anything structural. The question is whether you have a ventilation problem or a heat problem, and in a lot of these older semis it is both.
Before you buy a dehumidifier, check whether the trickle vents on your windows are actually open. I know that sounds patronising but I found mine had been painted shut when I moved in and I did not notice for two years. Also check whether there is an airbrick on the external wall near where the patch appears. If it has been rendered over or blocked, that alone could explain it.
If the humidity stays above 65% even with the heating on and a window cracked, then yes a dehumidifier will help, but it is treating the symptom not the cause. A decent one will cost you £150-200 and add maybe £40-50 a year to your electricity bill, which is not nothing.
PS - happy Valentine’s Day to anyone whose idea of romance is reading about damp on a Saturday morning
Quick update on this. Opened all the trickle vents like @greenwhistle_hants suggested and stuck a cheap dehumidifier in the hallway. Hygrometer is now reading 58-62% most days. The patch hasn’t gone completely but it’s definitely lighter and not spreading. Going to leave it another couple of weeks before I decide whether to repaint or just live with it.