Damp in garage wall

[Marineboy]

My son has just moved house and has a problem with his garage. It is brick built and the short side looks to have been built up against a concrete slab, or possibly the slab has been laid after the garage was built. The slab is 150mm, so is directly in contact with the bottom two courses of the garage wall. The inside of this wall is damp, so the assumption is that the slab is holding/directing water against the brick.

We have started to dig out the slab where it immediately abuts the wall, with the idea of creating a gap - see photo. However, the concrete is proving extremely difficult to remove. Is there another way of solving the problem. I was thinking somehow of laying a strip of DPC material along the junction but not sure how or if this would work.

Any ideas welcome.

 

[SammyQ]

Where is tbe damp course in your photo please Marineboy?

Sam

 

[Marineboy]

Where is tbe damp course in your photo please Marineboy?

Sam

Hi Sam, I cant actually see a dpc in the garage wall. There may be one under the slab that the garage was built on.

 

[Oddbod70]

Youve got your work cut out trying to do that by hand. I think you are on the right track buy creating a gap, esp if its only that one wall thats damp. That suggests that the slab rather than a lack of damp proofing Is a lot of the problem. how thick is the garage wall? Half or single brick?

i think id be hiring a concrete cut saw and a small breaker for a day to do that. A couple of hours, assuming you can get at it.

 

[RichardG]

I would hire in a big disk cutter, ideally one designed for this sort of work, and then cut straight down the edge of the wall. You can then just lift out the offending piece. I paid £20 per day for the last one I hired.

 

[Ttrees]

What's the solution if there is no damp course?

 

[Daniel2]

What's the solution if there is no damp course?

Put one in retrospectively, between the concrete slab and the garage wall.
I would suggest going down around 50 cm below the garage floor level.

 

[owen]

The other option is to just tank out the inside of the garage wall with k11 slurry and then a coat of renderlight over the top

 

[SammyQ]

Superficially - remember we're only looking at one photo - my guess is that the concrete higher outside than the garage floor inside is bridging a DPC/DPM. The fact that the majority of the garage is dry suggests there IS one. Regretably, I think you are going to have to keep digging. A 9" angle grinder MIGHT be man enough (with a diamond blade) to get through that slab about 12" out from the wall, but I agree, a trolley mounted saw is probably a better option. A midway alternative would be one of those petrol driven, hand-held, saws you see workmen opening holes with in roadways or pavements. That and a bl**dy big crowbar or pickaxe!!

Sam

 

[Oddbod70]

What's the solution if there is no damp course?

Good question ttrees! Its why i asked what the construction was. If its only that one wall that is damp then it may be just be ventilation thats keeping the damp at bay. One of the driest garages I ever saw was only single brick, but must have had a really clear gap between the inner and outer leaves And exactly the right amount of air going through.

 

[SammyQ]

"Put one in retrospectively, between the concrete slab and the garage wall.
I would suggest going down around 50 cm below the garage floor level."

Two things Daniel (in the absence of our resident architect, I hope I get this right):

1. If you do not seal or tank the new DPC/M to the wall properly, it will conduct water up the wall face by capillary action, back to square one.

2. 50cm seems perilously close to the same depth of any actual founds that the wall of the garage is built on. LOAD of labour too, to get down that far. MikeG used to recommend 2 bricks depth below a DPC/M if you were in a tight spot, like here. Not pretty, or ideal, but it would do.

An air gap, far enough down - two bricks?? - will prevent water ingress, just make sure the trench created drains well, otherwise your new pond will just perpetuate the problem.

I had this exact problem with a neighbour's flower bed(*$*!) and raking the soil back cured it.

Sam

 

[Marineboy]

Thanks for all your replies folks. The garage is single skin and there is no sign whatsoever of damp in the other walls. I was hoping for a quick and easy fix but I guessed there wouldn’t be one. Hiring a concrete cutter seems to be the way to go. Thanks again.

 

[SammyQ]

only single brick, but must have had a really clear gap between the inner and outer leaves

Do you mean "faces" instead of "leaves" OddBod? A single skin wall cannot have two 'leaves'?

I agree, ventilation is a very good preventer of damp, my present garage has gaps all the way round because of corrugated roofing. BUT, and it's a very BIG but, in claggy (cold, high humidity) winter weather, you get hypothermia dead easily AND the (small) amount of condensation on tools encourages tinworm.

Sam

 

[Oddbod70]

Do you mean "faces" instead of "leaves" OddBod? A single skin wall cannot have two 'leaves'?

I agree, ventilation is a very good preventer of damp, my present garage has gaps all the way round because of corrugated roofing. BUT, and it's a very BIG but, in claggy (cold, high humidity) winter weather, you get hypothermia dead easily AND the (small) amount of condensation on tools encourages tinworm.

Sam

Sorry, my confusingly poor choice of terminology. in the garage example i was thinking of the walls were Only single brick thick but done as two seperate leaves tied together with ties (i sincerely hope!). so in practice it was a wall with a tiny cavity. I have no idea why, or even how it was done TBH, but it was clearly built by someone with a reasonable level of skill. My theory was that the tiny cavity was mainly clear and the lack of a full wall plate allowed it to stay dry.

There was ventilation, but not howling gale level, and there was very little condensation. I can‘t believe it was designed, I think it must have been a brilliantly lucky accident. Ive always wanted to try a recreate it, but I've never had the opportunity.

edit. Just for clarity i know is was sinle brick thck cos the “wall plate“ was a row of wierdly spaced flemish bond!

 

[Lons]

Pretty much what the other guys said Marineboy, ( where in Northumberland are you btw, I'm near Morpeth? ).
Assuming there is a DPC and you should be able to find that by careful searching and maybe a little raking with the edge of a cold chisel, you need ground level to be at least 150mm below that DPC so no alternative except to cut back the concrete slab and I'd recommend going a bit deeper and dropping in a length of field drain covered in pea gravel if you want a permanent solution though you also have to consider where you direct the water from that pipe.
Hiring a big cutter is the easiest solution but it is possible to cut a slot with a 9" grinder / diamond blade and then chop down with a 100mm cold chisel. There's no effective way to tank the wall without getting below the concrete anyway so has to be done.

cheers
Bob

 

[Marineboy]

Thanks Bob, I’m in Blyth. The field drain idea is a good one but I think what we’ll do first is create the gap and see how that works out.

 

[Lons]

Sorry, my confusingly poor choice of terminology. in the garage example i was thinking of the walls were Only single brick thick but done as two seperate leaves tied together with ties (i sincerely hope!). so in practice it was a wall with a tiny cavity. I have no idea why, or even how it was done TBH, but it was clearly built by someone with a reasonable level of skill. My theory was that the tiny cavity was mainly clear and the lack of a full wall plate allowed it to stay dry.

There was ventilation, but not howling gale level, and there was very little condensation. I can‘t believe it was designed, I think it must have been a brilliantly lucky accident. Ive always wanted to try a recreate it, but I've never had the opportunity.

edit. Just for clarity i know is was sinle brick thck cos the “wall plate“ was a row of wierdly spaced flemish bond!

If the tie bricks are flush each side then the cavity cant be more than 25mm i.e. a brick is nominal 225 x 100 x 75 and it's difficult for a brickie to keep that clear of mortar droppings unless it's filled with insulation though it can be done with care and would keep the inner leaf dry.

 

[Lons]

Thanks Bob, I’m in Blyth. The field drain idea is a good one but I think what we’ll do first is create the gap and see how that works out.

I'll drop you a pm with my mobile number if you want advice and if you need it I could always nip over and look at it as long as we can social distance as my missus is recovering from an op. You're lucky as there are several hire centres around you where you can get a cutter.

 

[RobinBHM]

Sometimes concrete paths against a wall can create damp by rain splash despite dpc being above the concrete.

If that's the case a professional waterproofed based on silane / siloxane would help.

If dpc is below concrete.....you've only got option of cutting concrete back, putting in new dpc higher ( which depends on internal floor level) or covering the wall internally.

 

[Daniel2]

"Put one in retrospectively, between the concrete slab and the garage wall.
I would suggest going down around 50 cm below the garage floor level."

Two things Daniel (in the absence of our resident architect, I hope I get this right):

1. If you do not seal or tank the new DPC/M to the wall properly, it will conduct water up the wall face by capillary action, back to square one.

2. 50cm seems perilously close to the same depth of any actual founds that the wall of the garage is built on. LOAD of labour too, to get down that far. MikeG used to recommend 2 bricks depth below a DPC/M if you were in a tight spot, like here. Not pretty, or ideal, but it would do.

An air gap, far enough down - two bricks?? - will prevent water ingress, just make sure the trench created drains well, otherwise your new pond will just perpetuate the problem.

I had this exact problem with a neighbour's flower bed(*$*!) and raking the soil back cured it.

Sam

I agree, Sam.
I was thinking more about this stuff ....