I am looking to renovate my garage a little and have an issue with damp in the back right corner. It is an exterior garage of single brick wall construction so appreciate it is never going to be 100% dry, however in winter the corner actually becomes a puddle so I was looking for any tips on how to remedy the situation as best as possible.
Pic of internal corner;
Corner.jpg (189.09 KiB) Viewed 2848 times
Pic of exterior drainage channel (apologies for mess but just finished sanding and repainting window!);
Exterior.jpg (58.94 KiB) Viewed 2848 times
I plan to clear the exterior channel which appears to be blocked with clay at the lowest point so I am unsure if it is attached to drainage or meant to be a soak away. I will poke around with a coat hanger to see if I make contact with any pipework, however in the meantime is there any damp proofing for brickwork that will help whilst keeping the look of the bricks (i.e. not tanking slurry)?
Do you know when the garage built? Are you able to identify an existing damp proof course/membrane? I’m pretty sure I can see the mortar line where the DPC is located on your internal picture.
If I’m right, and you can then you should start by ensuring that the external ground levels are no less than 150mm below the DPC. This will depressurise it and prevent what is know as splash back. You can consider installing a french drain (basically a gravelled filled trench) Don’t waste your time with chemical damp proof injections, they are a waste of time unless what you are experiencing is true rising damp and such a thing is not as common as many builders/damp proofing contractors will have you believe. Providing you can maintain external ground levels being lower than the existing damp proof course (if there is one) or lower than the internal floor levels, you should then consider managing ventilation and temperature within the structure. It is single skinned therefore it will be susceptible to cold spots which can lead to condensation in the colder months.
These users thanked the author Surveyorman for the post:
Thanks for the response Surveyorman. Unfortunately no, I am unsure when it was built. House is circa 1930's with a drive that leads up to it so maybe original. I have looked closely internally (pics below) and it looks like there is a DPC, but only going one brick up inside (7-8cm). Measuring from the window it appears a concrete gully is actually built up an additional 7cm externally meaning the concrete is likely at the exact same level as the DPC It is downhill to that corner externally and outside was extremely overgrown when we purchased so I guess over the years the gully got clogged up and any dampness unable to soak away has crept into the brickwork and with little to no DPC, that is why we are left with a puddle!
It's annoying as the garage is in pretty poor nick really so do not want to throw money at it given in a couple of years I probably will tear down and build an extension to the house in its place. It would just be nice to have a fairly dry garage in the meantime. I am now thinking to scrub down the concrete gully, as there is a lot of moss that must be trapping moisture and trying Thompson's Water Seal on the outside. Bit of a bodge so if you have any tips I am all ears
Ok, so the issue here is that the damp proof course of your garage (there is definitely one in place here) is being bridged by the external ground levels. Good building practice is to ensure that ground levels are at least 150mm (2 brick courses) below the level of your DPC. Your suggestion of Cleaning it out will not really “cut the mustard”.
You need to look to either lowering the external ground levels or installing a French drain where possible.
A French drain is essentially a shallow trench filled with gravel.
Dig your trench 150mm below the DPC level and circa 150mm wide. Back fill this trench with pea shingle gravel. It may also be beneficial for you to line your trench with a geotextile membrane to prevent the earth “bleeding” back into your trench. Take care not to fill the stones above the level of your damp proof course.
Once you have done the above, you will have succeeded in “relieving” the damp proof course thus allowing it to function unimpeded. See how this affects the internal at times of heavy rainfall before you decide to do anything else to the garage.
Your DPC is irrelevant for protecting the solid floor and any masonry below the DPC.
There's no membrane (DPM) present and then there's that plinth/ledge effect on the outside. The ledge will be catching and holding rainwater and allowing it to penetrate through the single brick skin onto the slab inside the garage.
The ledge will also be absorbing water from the channel.
Your outside pic shows two step downs which suggests that you are on a slope or a hillside? Is there a retaining wall nearby?
Ground water coming down a slope is very difficult to deal with.
The drainage channel invert is almost level with the slab floor (FFL) and it might be helping cause rising damp and penetrating damp?
Clean out the channel and find and clean where it drains to.
These users thanked the author wes56 for the post:
Yeah - going to give a good clean out tomorrow and lifted a drain cover near the house that might link to it. Just unsure if it is a soak away at present so hopefully a poke around with a coat hanger will give me an idea if there is pipe down there - just so much clay and junk down there from years of build-up.
The garden is sloped and there is a retaining wall just behind the garage (pics below). In my eagerness to renovate the garage I detached an old gutter than went across the whole window (yellow dashes) and now have one going straight into the channel. With reflection the last owner probably did this to take as much water away from the problem area itself so I have probably just made it worse (will wait for next big rains to judge)
Just trying to do what I can before having to call someone else in so on with cleaning and poking!
The down pipe seems to have an angle fitting t the bottom ?
The angle fitting is pointing away from the channel, its pointing in the opposite direction.
With your location of garage and house you will probably continue to get excessive ground water coming down the slope.
Have you had a look under the floor in the main house rear elevation wall?
Lift the manhole cover, operate all toilets and taps and see where they enter the manhole.
If there's a spare inlet hole in the manhole side then push a hose pipe up there to free any clogged soil sediment from the channel perhaps?
No - I have not lifted the floor in the house yet (gulp).
I cleared the gutter and blasted the drainage hole, however it appears it is a soak away as I could not locate a pipe down there (had a good rummage around with the powerhouse. I lifted the drain cover and flushed, turned on all the taps and can now confirm the drainage is only for the house and a single drain in the middle of the garage floor.
You are quite right that the downpipe pipe is angled away to a drainage channel on the other side of the garage and that seems to be working (i.e. diverting most of the water away from the problem area!). One cheap and cheerful option I was considering was bitchumen paint?
Again, the water ingress is not severe in the garage and I wondered if bitchumen paint on the bottom couple of courses of bricks would help?
you wont be able to keep the water out with sealants or bitumen.
where is the angled downpipe fitting diverting water to? Anyhow, the main problem is ground water not water from the roof.
It is downhill to that corner externally and outside was extremely overgrown when we purchased so I guess over the years the gully got clogged up and any dampness unable to soak away has crept into the brickwork and with little to no DPC, that is why we are left with a puddle!
