Treated Dry Rot is growing again

[markwm]

18 months ago I discovered lots of dry rot growing under the cavity of our living room. It was all over the soil floor and up the walls, cause of it was due to the fact dodgy tradesman had left timber on the wet ground to rot...

At the time I got a specialist company in to do the work. Now today I needed to go under the floor to do some work on the radiator pipework and noticed that white mycelium dry rot is growing again on an area of brickwork about 600mm2. It's on the external wall, and obviously it's below ground level.

The company whom I paid to do the work offered a 5yr guarantee, but is it worth getting them back? Or should I attempt to tackle it myself? They failed once, so what's to say they won't fail again.

 

[Schoolmarm]

Are the original causes rectified? We need superMatt.


Is it ventilated at all under there?

 

[markwm]

It's extremely well ventilated, I've been down under there all morning and there's plenty of draft coming from air bricks.

 

[Schoolmarm]

Oh well done. Matt will be here soon hopefully with expert advice.

 

[biffvernon]

Ventilation notwithstanding, it's still too wet. Find more ways to stop the water getting in and remove what does get in.
The longlasting and effective treatment for dry-rot is low humidity.

 

[markwm]

It's impossible to stop the wall getting damp. It's an external solid wall below ground

 

[biffvernon]

So the timber needs to kept isolated from the permanently damp masonry. Even 'dry' rot doesn't thrive on dry timber and it will die of hunger eventually if all it can eat is wet bricks.

 

[markwm]

Well, this is the thing. It growing on the wall and there's no timber anywhere near it. All the joist ends are sat on galvanised plates, thus not in contact with the damp wall. As you can see from the pic the dry rot is in the middle surrounded by masonry.

 

[biffvernon]

In that case I doubt whether you have a problem at all. The harmless fungus is probably feeding off organic material in the soil the other side of the wall and is just having a sniff round indoors to see what's what. Brush it off if it makes you feel better.

 

[Matt Green]

18 months ago I discovered lots of dry rot growing under the cavity of our living room. It was all over the soil floor and up the walls, cause of it was due to the fact dodgy tradesman had left timber on the wet ground to rot...

Really? If so, the ground would have to be very wet indeed and wet with fresh water too. Have you got a high water table beneath that floor? Local water courses? A drain behind that wall?

At the time I got a specialist company in to do the work.

What exactly did they do? I can see they replaced the joist ends and removed the fluffy mycelium, what else? It might be important. Check the terms of the guarentee, what does it say about keeping the building in a watertight condition? They might well come back and spray the mycelium for you, that really should be all they do and all they offer to do. Getting rid of sub-floor dry rot is difficult because as Biff said, it's feeding on humus in the soil. He's also right in as much as it isn't doing anything. It's forming strands to stop it dehydrating and there is no timber around for it to damage.

Scrub it off with a wire brush and keep checking on it would be the best bet, guarentee or not. It will stave eventually, but it might take a while. I certainly wouldn't pay for any more work. I hope you didn't pay too much for what you did have done. I am curious as to why it's so wet under that floor though.

M.

 

[markwm]

You pretty much got is spot on. Very high water table. There's a natural spring somewhere nearby.

The cavity under the floor is deep as well, 4ft probably so the soil will be 'damp'.

Company replaced joist ends, treated timbers, removed dry rot, sprayed everywhere with some form of treatment. However, I do notice odds little bits of timber left on the sub floor. Seems they didn't remove them all and I myself have removed some afterwards.

If I scrub it off with a brush, should I spray the wall with something? I have some cuprinol 5 star in the garage?

 

[Matt Green]

Cupranol is a wood treatment: I would just wire brush it off, remove the strands from where they fall and check the wall again in a few month time witha view to doing the same. Pretty much any commercial fungicide will kill the mycelium if you want to (and it might make it easier to remove if it's stubborn).

M.

 

[Penners]

It's forming strands to stop it dehydrating

Matt, could you explain that behaviour a bit more, please? Are the strands hunting for water?

 

[Matt Green]

It's forming strands to stop it dehydrating

Matt, could you explain that behaviour a bit more, please? Are the strands hunting for water?

No: food (wet wood), always food. From the organism's point of view, why look for anything that isn't going to provide you with energy? It might find a lake, but it would still die. The formation of strands have been looked at by people much more able that I, but the short version is that they have less surface area than the same volume of individual hyphae and so lose less water to the atmoshpere as a result. It's a survival adaptation and you see less when when dry rot is happy.


M.

 

[Penners]

Thanks for the explanation, Matt. It's a shame that markwm's dry rot isn't very happy...

 

[markwm]

I'll brush it off and then spray the wall with fungicidal wash. Thanks guys

 

[biffvernon]

fungicidal wash.

If you are really intent on murder just use some bleach - it will kill any fungus just as effectively but will leave less of a nasty taste on the planet. (And it's much cheaper.)

 

[Penners]

bleach.....will leave less of a nasty taste on the planet.

Really? Is bleach relatively innocuous, environmentally speaking?

 

[biffvernon]

Relatively yes, once it's done it's oxidising work there's nothing much harmful left, whereas a fungicide may have a lasting biocidal effect.

 

[Penners]

That's worth knowing. Thanks Biff.