Use DryRods to resolve failing mortar below DPC?

[lemoncurd99]

My garage wall is shared with next door neighbour's house. My side is exposed bricks with concrete floor; there is clearly a traditional bitumen DPC (the long strip type) in the brickwork about 3 courses up from the floor and it is working - bricks above DPC are bone dry. Alas, the ~ 3 courses below this DPC are wet and the mortar is failing - turning to dust and falling out. Some quite large gaps in the mortar along the whole stretch of the wall.

Neighbour's (suspended) floor is clearly above DPC as nothing to see his side; he has plastered walls in a decorated room, with no damp issues.
Have investigated roof above and other sources of damp ingress, no evidence of any nefarious source. Architect family member thinks it is just ground moisture.

Planning to install Dry Rods at lowest course of mortar above my garage floor (prob 30mm up above concrete), wait a few weeks, and then re-point the entire 3 courses. My questions:

1. Does this sound like a reasonable remedy?
2. Do I really need the scraper-out tool to remove debris after drilling, or will a quick suck with Henry hoover suffice?

Thanks in advance

 

[JohnD]

1. Does this sound like a reasonable remedy?

No.

Dry rods will not work, but I can sell you some magic beans that will be equally effective.

 

[JohnD]

2. Do I really need the scraper-out tool to remove debris after drilling, or will a quick suck with Henry hoover suffice?

You do not say how old the wall is, or what kind of mortar.

However

It is quite common for lime morter to be softened, and actually washed away, by long term water leaks.

In the absence of other evidence I will guess that is what you have.

Perhaps you had a spilling gutter, a blocked drain, or a leaking pipe. I hope you have found and rectified the fault.

I find a good treatment is to wash out the joints with a hose. The soft and useless material will wash out. Underground, the joints are often full of mud.

Once you have removed the perished material (and hopefully the wall has not fallen down) and the bricks have started to dry, you can repack them with a stiff mix of sand and cement mortar. As you work, it may soften and become wet as it absorbs water from the bricks. If they are too wet, you will have to wait for them to dry out more. If the perished mortar is very deep, clean out and repack small sections at a time, not next to each other.

There is no objection to using cement mortar underground, because buried mortar does not "breathe" as old lime walls above ground can.

Cement is not softened by damp, it will actually help it grow stronger.

 

[jj4091]

Ours has been like that for 25 years that I have lived here and never got any worse I used to be concerned about it but don't worry any more.
Is yours a 1940's house like ours as they seem to have put DP course in brickwork but not damp proof membrabe under the concrete and I assume that is how it was done then. So unless you are prepared to dig up the garage floor to resolve it then just live with it. I painted the lower courses of bricks with floor paint which may or may not have stopped it getting any worse.

 

[lemoncurd99]

Thanks both. It's a 1967 wall and assumed sand/cement mortar, probably with a small cavity, although hard to tell. Could well be to do with the concrete floor not having a membrane and abutting the bricks, therefore creating a 'bridge', although the concrete floor itself does not seem damp...

 

[JohnD]

Very strange that the mortar has eroded, then.

You can still repack it if you want.

 

[lemoncurd99]

Yes, think I will scrape out the mortar and re-point/pack it and take it from there...

 

[ree]

OP,
Why not post detailed pics, & context pics? Perhaps a pic showing the ground level outside the garage doors?
Grinding or raking out the beds & perps to 25mm depth might help below the DPC?
Careful not to damage the existing DPC
A 3:1 semi-dry sand & cement mix could be used for mortar pointing below the DPC.

I'm not keen on Dry Rods although some have found them worthwhile? In your case they would be useless.

 

[stuart45]

I'm not keen on Dry Rods although some have found them worthwhile?

A mate of mine has used them on some of his houses. He buys old run down Victorian properties and does the work and rents them out.
He's been in the trade since leaving school as a thatcher, so is used to old properties. Even back in the 90's, he was advising people to use lime render, lime plaster and breathable paints, so he understands how old buildings work.
However, with dry rods, he's found them to be effective on some really damp walls when used in combination with lime plaster.

 

[lemoncurd99]

Here are some photos. The first photo is taken from the inside of my garage. The DPC can be seen where the bricks change colour and the failed mortar is shown as powder on the floor. I have not 'raked' out the mortar; it falls out itself and I periodically sweep it up. The two small/circular stains on the right hand side of photo on garage floor are oil from my bicycle. The other darker patches on the concrete floor toward the left of the picture could be discolouration or could be ground moisture.

The second photo is taken from outside my garage's rear door showing this wall as "2 bricks" wide; this photo projects into the neighbour's garden over the dividing wall (the boundary is not aligned to the edge of my garage, so my garage dog-legs into next door. This photo shows 3.5 courses of bricks below the DPC.

 

[stuart45]

It's ground salts that break down cement mortar. When they get to the surface and crystallize. It's the same with brickwork on the seafront where the salt air affects the joints.

 

[ree]

OP,
Why not do what I suggested in post #8?

 

[flameport]

External paving has been installed right up to the wall, so there is no ventilation - water will run off of the paving into the wall, soaking it, and there is nowhere for the water to escape.
Remove the paving that's against the wall and replace with gravel.

Paving level is also too high, should be at least 150mm below the DPC, although that isn't the cause of this problem.

 

[ree]

Poster #13,
I think that you are referring to the neighbour's wall?

 

[lemoncurd99]

OP,
Why not do what I suggested in post #8?

Yes, I think I will. Going to get some supplies this week and give it a go (first timer)