Damp even with injection treatment... what factors to consider?

[d000hg]

Much of our Victorian house has had injection treatment but in a couple of places we have damp regardless - mainly in our utility room which is clearly a later addition. Initially I figured the treatment had simply failed but a handyman mate suggested otherwise and I think there are two possible factors, I'd welcome input on from more expert folk...

1. The house generally has the internal floors 6-12" higher than the ground outside i.e. the bottom course of bricks has ventilation bricks to the under-floor void. I assume this is done for good reason so that damp has to rise rather than being able to penetrate from the soil, is that correct? I notice the utility room, clearly a later addition, doesn't work this way. The room has a concrete floor seemingly at ground level so the row of injected bricks is actually one or two courses higher than the internal floor. To me that suggests it will not stop water coming up the bricks and into the concrete, i.e. it will stop the damp climbing up the wall but won't keep the room dry?
2. The outside of the house on this side has a large concrete yard which comes right up to the house. My mate says this gave rising water nowhere to go, and helped it get into the house. He suggested a fix is to cut a channel 6-12" wide around the house, filled with gravel, presumably to act in effect as an air-gap? In fact with my previous point this would actually sort of 'lift' the floor inside higher than the ground outside too.

Is my educated guesswork correct and is his suggestion sensible?

A related issue is that where the socket is in this room, the damp appears to have climbed from the floor up and around the socket. Is it plausible that fitting this cable has breached the injection treatment?

 

[chappers]

yep all sounds plausible and reasonable.

 

[chris1982]

Have the walls being replastered after the injection? Otherwise they might still contain hygroscopic salts.

 

[d000hg]

Have the walls being replastered after the injection? Otherwise they might still contain hygroscopic salts.

I couldn't say though based on the age of the treatment, state of the decoration, and the fact the previous owners talked about doing some pretty major renovations, I would expect they HAVE in this particular case.

 

[chris1982]

If the DPC is above the floor, they also should have tanked the walls from the floor to (just above) the new DPC level.

 

[d000hg]

Maybe that wasn't done, I think the DPC is getting on 20 years old and I'm not sure if there was as much choice back then? Presumably with a solid concrete floor, that too should be tanked if I want to try and improve matters, up to a height of a foot or so up the wall?

We have been considering replacing the laminate floor with tiles so perhaps we'll take the units off the walls and do this properly. Possibly a good place to learn some skills as ultimately it's just a utility room so if it's a bit crappy, not the end of the world!

 

[chappers]

a 20 year old injected course could easily have failed by now if it ever worked.

 

[d000hg]

Is there an obvious way to tell if that is the reason? And can they be re-done or do you only get one 'go'?

 

[Blagard]

One way to check is to get hold of a meter and check the walls yourself. You can buy a meter on amazon but don't take the readings literally, they are OK for comparative readings so the reading high up on an internal wall should give you a dry reading. e.g. one I have seen on amazon

https://www.amazon.co.uk/Proster-Mo...ring-Cardboard/dp/B01AAAL9MM/ref=sr_1_1_sspa?

 

[d000hg]

Oh I have one - great fun - but I meant to establish if the damp is due to failed injection course, or a scenario such as I described in my first post, that the water is getting in despite the treatment.

Presumably if the damp does/doesn't extend higher than the top of the injection course is a big clue.

If it extends higher only in one or two places e.g. up the course of a cable, that suggests the cable has breached the course?

 

[Doggit]

But what makes you think you have damp, as you haven't descibed any of the symptoms. You say that it has climbed up round the socket, and so yes, if it was injected, and then cement rendered, then putting in a socket would have brocken the "seal". What you would do there, would be to remove the electrical back box, paint the hole with bitumen, and then repalce the backbox; the surrounding area should then dry out, but might retain salts that would then atract moisture in the room. It's more than likely that a DPC was put in the concrete floor when it was installed.

Even if the old injection has failed, you can inject the mortar course with a silicone cream, and it's a DIY job, but you may need to add a cement render with a waterproofer in it to go between the injected course, and the floor.

As to the outside floor level; if it is too high, then you can cut a 6-8" channel that will go down below the inner floor level, but fill it with 1" stones, as gravel will get filled with earth, and track the water across.

 

[d000hg]

The main sign it's damp is the feeling of dampness... Also I used a damp meter and there is flaking paint

Thanks for the suggestions and advice... Most helpful.

 

[Doggit]

he main sign it's damp is the feeling of dampness.

Actually, unless it's very wet, it's sometimes difficult to judge whether it's damp or just cold. And flaking paint can be the result of poor workmanship. The average moisture meter doesn't tell you much in brickwork, and in truth, even the good quality professional damp meters don't tell you great deal more. Then you can get caught out where there's filler, as that will attract moisture from the air more so than plaster does. It can be a bloody minefield at times, and I've seen the professionals hack of a wall, and then look perplexed. I did a job recently where they said the wall was damp and needed a DPC, then found that the previous owners had taken the bonding down to the floor, and it had wicked up moisture from the concrete floor, and the wall was fine.

A lot of it is down to experience as well, but that's not to detract from the fact that you may well be right.