Some dry rot in a bathroom floor joist

[AndersonC]

I'm ripping out the old T&G pine, ready for 25mm ply for tiling on.

The end joist, shown in the pics, has some dry rot present along the top edge. This can be seen in the second photo, at the left hand end where it's about 1/4" deep. It has also penetrated where nails have held the boards down.

This is probably a combination of water getting at it (it sits under the pipes) and poor ventilation.

I need this sorting fast, would the application of a decent timber treatment (cuprinol) stop it spreading through the joist?

I can improve the ventilation in this part of the floor also, is this recommended? And I can most certainly prevent moisture getting to it by sorting the plumbing good and proper!

I'm off to get some Cuprinol now, however I could do with your suggestions. The joists are 5"x3" and this one spans about 6 feet.

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• AndersonC
• 6 Aug 2008
• 3

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• AndersonC
• 6 Aug 2008
• 2

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• AndersonC
• 6 Aug 2008
• 2

Thanks

 

[JohnD]

you have to cut out and replace all affected timber, and timber in contact with and beyond the affected part (wrap it in polythene to carry it away for disposal, vac up the dust). the spores and roots are very pernicious

Cuprinol make good preservers that you can spray onto nearby timber and brick

You must treat the replacement timber too

There should be guidance around http://www.cuprinol.co.uk/products/products_treatment.html though I don't see their dry rot liquid on that page, perhaps they have taken it off the DIY market. You can drench the sound and new timber in Green Preserver. try http://www.cuprinol.co.uk/advice/index.html

 

[AndersonC]

Cut out and replace? Oh dear!!

I'll get more of the boards off and see how the rest of it looks. Is there an easier option than replacing the whole joist?

Anyway, thanks for the response Mr D.

 

[JohnD]

for a 6' joist, taking it out and putting in a new one sounds much easier than trying to joint it.

I've only had wet rot myself. Do you see tendrils, fluff, red dust, fruiting bodies, cubical cracking of the timber?

Poke it with an old screwdriver and see how deep it goes. It may have travelled along teh laths of the ceiling below.

 

[AndersonC]

I've pulled up a fair few boards now.

Approx 18'' of the end joist (4-5 board widths) are affected at the left hand end of the joist as indicated in the pictures in the OP. At the other end of the same joist, there is an area mildly affected which is about 1 board width. This lies below the toliet supply plumbing. There are none of the characteristics which JohnD has described to indicate the presence of wet rot; from previous experience in my parents house this looks like dry rot.

Anyway, the remainder of this joist (a good four feet, and the other joists seem sound, when poked hard by a screwdriver.

I am endeavouring to vacuum up the dust but can't get the nozzle into a tight space behind the affected joist.

I have acquired ronseal treatment, as I could not get hand of cuprinol. According to the 'strapline' this should do exactly as it says on the tin (so I won't go throwing it in rivers

I will treat all the timber I have uncovered in the floor and the L+P ceiling attached to it for now and see if any further advice pops up. Boards are off for chiminea fuel (when the bl**dy sun comes out!)

Thanks a lot.

 

[gregers]

well all infected timber needs to be removed and replaced with new tanilized
timber,ceiling should be taken down and walls treated etc etc etc,but if your not prepared to do all of that and you think just spraying the stuff around will work,maybe it will maybe it wont???but reinstalling everything in your bathroom then for it to reemerge your going to be 1 happy bunny 'not'.the joist ends will no doubt be totally rotten and the wall plate.but if you have absolutely no chance of removing said timber it might be worth drilling into it and injecting it with the dry rot fluid,this way you ensure the heart of the timber is treated not just the 3mm on 3 sides.

 

[AndersonC]

well all infected timber needs to be removed and replaced with new tanilized
timber,ceiling should be taken down and walls treated etc etc etc,but if your not prepared to do all of that

No chance. I am working on the bathroom at the moment. Ripping the kitchen ceiling out is a definite no no.

and you think just spraying the stuff around will work,maybe it will maybe it wont???

I am not "just spraying the stuff around" I am applying it very thoroughly to the timber by brush. Maybe it will work???

but reinstalling everything in your bathroom then for it to reemerge your going to be 1 happy bunny 'not'.

Quite true, if I assume you mean "you're going to be 1 happy bunny 'not'."

the joist ends will no doubt be totally rotten and the wall plate.

Quite an assumption. One end of the joist is fine as it sits under part of the landing and I have part of it exposed from another job. The other end, which fits into the bathroom wall may be rotting, however I cannot find out without destructive inspection. It appears to be a very localised attack which may indicate it is rather new. By stepping in now and heavily treating the affected (and surrounding) timber I may have been lucky enough to prevent a spread to the extent you describe.

but if you have absolutely no chance of removing said timber it might be worth drilling into it and injecting it with the dry rot fluid,this way you ensure the heart of the timber is treated not just the 3mm on 3 sides.

Right, this I will do. I have applied three coats to the outside of the joist so far. I have also treated the sound L&P ceiling and the new ply I am going to fit over the floor.

What I am certainly also able to do is get some air bricks fitted within the vicinity of this floorspace to ensure it is ventilated, there are currently none.

 

[skwdenyer]

If you're fitting air bricks you're going to have a cold floor / ceiling! At the very least you need to lag those pipes, otherwise they could freeze (and anyhow it is just good practice).

If you want to ensure water absolutely can't reach this or any other area again, you're going to have to do better than chipboard / ply + tiles. You'll need to properly tank the entire bathroom.

Also, if these are just 5" x 3" joists, I would have thought they'd be a little flexible to tile on the ply. At the very least you might want to glue and screw the ply down, and perhaps fit some cross-noggins first (difficult with the ceiling in-situ).

What I've done in the past for a bathroom with similar joisting is to reinforce the sides of the joists with steel (glued and screwed in place) before replacing the floor - makes a huge difference, stops the tiles / grout cracking, and so on.

 

[Lower]

Can't see any signs of dry rot in that photo. Just wet rot that has dried.

 

[ladylola]

To be honest I was thinking the same, it doesn't really look like dry rot. Another name for dry rot is "cubic rot" because simply put the timber forms into little cubes as it is attacked and moisture is drawn from it. Internally you would normally find the mycilium or fungus threads running between the cubes and the whole thing becomes fragile to touch.
Working on heritage buildings we used to come into contact with this quite often and whilist nowadays it's not normally treated in the past we used mayonaise paste on timbers that just could not be removed. I'm not sure if you can still get it but it may be worth a call to a specialist.

 

[gregers]

well i use pro bor 20 from safegaurd chemicals very similar application as the old mayo paste that we used to use back in the day.
both dry/wet rot do cuboidal cracking.

 

[AronSearle]

Dry rot still needs moisture to continue to grow, what it does however is transport moisture from the wet areas of timber, to dry areas of timber allowing itself to spread. The fungus will also possibly take moisture from the wall, and transport it to the timber though it's ability to do so is limited, but the masonry itself should be dry or isolated from the timber.

If you remove the source of moisture, and dry the timber, you stop the dry rot. The spores are already present in nearly all buildings and the air itself, so you don't need to treat chopped out bits of timber like they are highly infectious.

The general advice of chop it all out +500mm of sound timber, is just that, general.

In many historic buildings such advice would be considered far to inappropriate. Often the dry rot itself is scraped away, (and where the beams are exposed and aesthetic, new slivers of timber is spliced in or resin repair is used), and the drying of the timber is closely monitored.

Treatment will at most penetrate a few mm's, it is only used to help protect the timber during drying. Even rod injections are limited and generally unnecessary.

If the other joists are not showing signs of moisture, it is more likely leaks or condensation from the pipe dropping water onto the beams top edge, extra ventilation of the floor should not be necessary, instead fix the leak or lag the pipe.

If I understand you correctly the rot is only 1/4" deep on the top of the joist, scrap this away, dry the timber, and re-level the surface of the joist either with resin or timber planed in to fit. The rot will not become active again without a source of moisture.

The joist is probably oversized and can afford to lose that depth on its cross section, but that is really for an engineer to comment on.

Do not seal the timbers back in until they are dry.