damp in 1850 farmhouse

[adamjseed]

Hi all,

I have an old 1850 farmhouse which suffers badly from damp. Its been neglected for the past 10 years. It is sold wall and rendered outside. It has been chemically injected into the brick some time ago but that has obviously failed.

What im thinking of doing is getting a new damp proof course as advised by a local company, which is injected into the mortar. This involves removing a degree of plaster. They then said they would re-plaster but im thinking of removing all plaster and using thermal board to add thermal properties to the house.

Is this a sensible approach to damp proofing - is there anything else I could do. Its really bad.

 

[JohnD]

Chemical injection is not much good, as you have observed. However if you invite a salesman who sells silicone injection into your home, he will advise you to buy silicone injection. The render is probably causing a damp bridge anyway.

How high above ground level is the damp? Is it in all external walls? Is it particular rooms? Is it in internal walls?

how high is the ground level compared to the internal floors?

Is there a particular source of water, such as ground raised against the wall; sloping paving causing rain to run towards house, leaking gutters, drains or downpipes?

How difficult would it be to dig a French Drain against the wall?

 

[adamjseed]

Hi JohnD

So in the worse place its about 1/1.5 meters high. I would say its a combination of:
A sold floor
Poor windows probably letting in water
there was a well there along time ago


Something funny that happened recently, I removed the plaster from an internal wall and the other side, that was still plastered, got really damp. But has not gotten any worse and appears to be drying out now.

The ground level is about the same as the internal floor
Gutters and drains arn't great but im repairing them as i go along
I'm not 100% sure on a french drain, but the side where it is worse is the only side where there isnt a concrete path right up against the house.

Just not sure where to go from here...

 

[JohnD]

I'm guessing the solid floor is either flags/bricks on damp earth, or concrete poured after the original wooden floor rotted. Most likely there is no DPM so it will be wet. One day you might consider digging it out and laying a better floor with DPM and insulation.

Does the concrete path slope away from the house, to carry rain away from the wall?

Exposing brickwork usually helps it to dry out by evaporation. In an old house, a good way to avoid damp walls is to achieve evaporation at a faster rate than damp gets into it. Render and drywall will have the opposite effect of slowing or preventing evaporation

On the wettest side, I'd suggest digging out a trench first (which will kick-start evaporation, and reduce water uptake by removing damp soil from contact with the wall) which you can later line and fill with pebbles. If the trench fills with water you have found a cause and can lead it away from the house to a soakaway or something. You may find the old brickwork needs thorough repointing as the old mortar may have washed away. Get a pointmaster gun or similar.

 

[adamjseed]

Actually the floor looks quite modern, its poured concrete with a plastic membrane under, I can see it at the edges. I dont think the floor was ever wood.

Ill try the trench and see what happens. Whats the most servere proofing? Can bricks be removed and replace with a membrane like the floor?

 

[JohnD]

it is possible to put a membrane or tanking on the outside surface of the wall, and I once did that before finding out that water will still get into the wall, upwards, from the foundation. You will do better to expose the brickwork so there is no wet soil against it, and it can dry out by evaporation. It is difficult for damp to travel up clean brickwork by more than one or two courses. Render and plaster help damp to spread.

On some of the anti-rising-damp enthusiasts websites, there are photos of brick bridges where the piers have stood in water for hundreds of years, and dutch warehouses by canals, and the water has not risen far.

 

[adamjseed]

Ok,

so it actually sounds like I shouldn't bother with a chemical damp proof course and try to dig a trench...

What would you recommenced to do on the inside? eg thermal board? should I use a membrane there?

 

[JohnD]

not sure.

With a solid floor, there is no chance of underfloor ventilation helping to dry it. You might use a sand and cement render, or lime plaster, on the inside rather than gypsum plaster, preferably painted with Supermatt (which is porous).

Also take off the skirting. When you renew it, screw onto plastic spacers so there is an air-gap. This will reduce the risk of rot.

If you hack off the plaster and render so it can air-dry, and do the trench, I am sure you will find the damp reduces. See if it becomes tolerable or if you need to do more.

If you put anything waterproof on the wall, it will hide the damp, but not cure it. Old houses work on the principle that damp will get in, so you have to ventilate it out. Lime plaster and lime mortar are "breathing" materials and much preferred.

If it was on a kitchen wall, you could leave the bricks bare, and ventilate the space behind units with air-bricks.

The water must be coming from somewhere. When you dig the trench you might find its source. Look very hard at gullies and downpipes which might be leaking into the ground, and at any old pipes.