Mould under cabin substrate

[captain flint]

1 hour ago, Alan de Enfield said:

Warm air holds more moisture

Indeed. And when it warm air holding more moisture comes into contact with cold surfaces, some of the water condenses. 

 

Tbh I'm just puzzling over it for the hell of it really, at the end of the day I think the main things will be air flow, and time, the finer details probably aren't that important. 

 

I can see even after 1 day of my original set up that it's having the desired effect, there are some fully dry patches in the bilge already. Obviously, I'm talking about the base plate rather than the substrate, which I'm sure will take longer to dry out, but it's definitely all going in the right direction

1 hour ago, David Mack said:

My guess I that with a 6ft+ wide baseplate in contact with canal water across the bottom of the bilge space the air you blow in will pretty quickly chill anyway, so it won't make any difference (except to your electricity bill).

Or in other words, any additional moisture which the warmed air picks up as it enters the bilge space, will be matched by a reduction in the amount of water that same air can hold once it has cooled down again, long before it leaves the bilge space at the other end of the cabin.

Good points. There will surely be *some* but it could well be negligible. Um, for all I know

[Tony Brooks]

18 hours ago, captain flint said:

That said, I can't be sure the inspection hatch is the only ventilation point. I've never seen any others, and I expect it is, but I can't be sure. 

 

On many boats, the floor is not sealed to the hull side or cabin lining, so there is a very good chance that there are other spaces through which air can enter the bilge. The same might apply around window trims on some boats.

[captain flint]

36 minutes ago, Tony Brooks said:

 

On many boats, the floor is not sealed to the hull side or cabin lining, so there is a very good chance that there are other spaces through which air can enter the bilge. The same might apply around window trims on some boats.

Thanks. Yes something I'd read on another thread on here on roughly that topic had raised that possibility. I'm adding in a desk fan at the aft end where the dehumidifier is, to help ensure a good through breeze

[captain flint]

So... I've hit a problem. I'll go into it below for anyone who wants to read about it/just to get it off my chest - but my main question is, is there any device that could help me work out where the steel struts/ribs in the bilge are? The ones the substrate* is fixed to. I'm wondering if getting the floor taken up and replacing the damp OSB board substrate with marine ply is something that can be assessed for do-ability before cutting into it, or if you can only really tell after you've chopped into it. I aware of stud/wiring/etc detectors, and am wondering if something like that could help here

 

*not sure "substrate" is the right word here but anyway. I think you will know what I mean. 

 

*

 

That's the short(ish) question.no need to read on, really. But if you want the long story, here you go:

 

We got the damp OSB under the floorboards dry. Took a few weeks, setting up fans and blowing air here and there and all that. Moisture meter readings finally got below 20%. 

 

We'd had to empty the main water tank at the start of the whole thing, as the tap between it and the pump didn't work and needed replacing (as did the pump itself). 

 

Then the very nice fella at the boat yard, was getting our ducks in a row for fitting the new pump. It was in a slightly different position compared to before, as there was no filter before. So he needed to check that the pipes all lined up. Which involved removing the end cap that we'd put on the pipe that attached to the pump outlet. 

 

There were indeed some adjustments needed, so he decided that the new tap and pump were going in the next day.

 

He forgot to put the end cap back on that night, though, before he left. He was thinking that since the main water tank was empty, there was no water in the system to worry about. This annoys me a lot. He has apogised. Which doesn't really help but blame doesn't fix things so we'll leave that aside. 

 

So... There was still a bit of water in the calorifier. And I didn't notice he'd neglected to replace the end cap. 

 

When I turned on the diesel heating system on that night, the increased pressure from the now heated calorifier meant an amount (?) of water burped out of the pipe. Onto the  dry substrate we'd been so painstakingly drying out.

 

In fact, it went right down a hole I had put in the substrate, to increase air flow for drying out the bilge. I had placed a little 12v fan there, but by this stage that had been removed it by then. So there was just a hole, perfectly placed near the end of the pups. So the water really got into the substrate better than ever before, following the tilt of the boat toward the stern, flowing along the underside of the substrate.

 

Admittedly it's a smaller area of damp than the patch that had built up slowly over time from a weeping pump. But now the moisture readings are higher than they were when I came into the yard with this problem in the first place. Over 50% in some places if you dig deep in with the prongs. Though I've got the topsurface fairly dry, barely above 20%. Used a heat gun. 

 

It's very annoying. 

 

A part of me thinks just wait for it to dry (as I said. I've got the visible substrate quite dry using a heat gun, but my moisture meter readings for deeper into it are still above 50% in some places. That's what you get, I guess, when instead of a very very slow leak, coming from above, you have a short, sharp leak, coming from below).

 

Problem with just leaving it to dry over time is that I don't really know how well ventilated it is. Maybe there's a gap at the edge, near the hull, as some lane said it's pretty common practice. Maybe they're isn't.

 

I could increase ventilation, I guess, with some more holes, though I don't really love the thought of blowing all those mould spores into the cabin (I had vented the extractor out of the boat when using the hole I've already got, not really possible to rig up once everything is back in place for various reasons) 

 

Hence me wondering about the feasibility of the fairly drastic measure of taking up a few more floorboards, cutting out the OSB that's damp (and is a liability, especially in the area near the tank and pump), and replacing with marine ply. 

 

I know it would be disruptive and time consuming but if it's doable I might be interested. Finding out where those steel struts/ribs in the bilge/hull would be a good start to working out of it can realistically be done. 

 

I would say answers on a postcard please, but that wouldn't be fair after writing this bleeding essay. If you've read this far, then thank you. Let's face it, those who haven't are probably wise! 

 

DISCLAIMER: My description of the latest leak is of course supposition, based on circumstancial evidence: missing end cap, position of hole, shape of damp patch, angle of boat, moisture meter readings. Seems the most likely explanation to me and the fella doing the work, but I appreciate that we can't be absolutely certain we know what happened. No sign of any further leak since, though. And yes, the end cap is back on. 

[Tony Brooks]

7 hours ago, captain flint said:

So... I've hit a problem. I'll go into it below for anyone who wants to read about it/just to get it off my chest - but my main question is, is there any device that could help me work out where the steel struts/ribs in the bilge are? The ones the substrate* is fixed to. I'm wondering if getting the floor taken up and replacing the damp OSB board substrate with marine ply is something that can be assessed for do-ability before cutting into it, or if you can only really tell after you've chopped into it. I aware of stud/wiring/etc detectors, and am wondering if something like that could help here

 

Unless this is just a shell with floor, it could turn out to be a much larger job than you think, because narrowboats tend to have all the bulkheads and partitions sat on the floor and often fixed to it.

 

Unless you can see signs of screws securing the floor, I fear stud detectors are the only sensible way for a DIY, and even then I have had very mixed results.

 

If the OSB is one of the damp proof ones, you may be best advised to leave it as it is and treat any mould. It could be more wet resistant than much so-called marine ply.

[captain flint]

1 hour ago, Tony Brooks said:

 

Unless this is just a shell with floor, it could turn out to be a much larger job than you think, because narrowboats tend to have all the bulkheads and partitions sat on the floor and often fixed to it.

 

Unless you can see signs of screws securing the floor, I fear stud detectors are the only sensible way for a DIY, and even then I have had very mixed results.

 

If the OSB is one of the damp proof ones, you may be best advised to leave it as it is and treat any mould. It could be more wet resistant than much so-called marine 

Thanks for your thoughts. It's actually a professional fit out, despite the materials used. Including rather hydroscopic OSB board, sadly, not water resistant at all. 

 

Pretty sure the bulkheads are attached to the floor but the area in question has no bulkheads, and I was wondering about chopping out the damp section, as opposed to replacing the entire substrate, which would, I'm imagine, involve taking out everything except the lining on the sides and ceiling, ie, bathroom, bulkheads, stove, galley - if it came to all that, I think I would be better off just selling the boat. It's in pretty decent nick. Or it was until this damp issue arose. 

 

But I'm not sure if chopping out just a section is really feasible, it might be that getting it dry is the only option. 

 

In terms of treating the mould, I assume you mean just the mould on the top side of the substrate, and basically ignoring the mould underneath, in the bilge? 

 

I do get that I don't live and breathe in the bilge, but I do worry that too get it dry it needs to be well ventilated, which basically, in effect, means getting air from the bilge into the cabin, so any mould down there might as well be in the cabin. 

 

Plus we've all seen a boat that looks OK but has that must smell of mould coming from somewhere unseen. It's not a good thing. If there's any way to avoid that I'd like to. 

 

It's a head scratcher

[Tony Brooks]

Cutting a section out is perfectly feasible as long as you can secure something to support the edges of the cut-out section all round to make an access trap, probably very similar, but larger, than what you have at the back of the cabin.

 

The bit you cut out will be scrap, so you can probe this by drilling a hole to establish the thickness of the material. Once you know that you can use a circular saw to a mm less and use that to cut around the rotten section, Then a Worx type vibrating saw/multi-tool to deal with the 1 mm. I think you can get a small plunge circular saws specifically designed for this type of job.

[captain flint]

20 minutes ago, Tony Brooks said:

Cutting a section out is perfectly feasible as long as you can secure something to support the edges of the cut-out section all round to make an access trap, probably very similar, but larger, than what you have at the back of the cabin.

 

The bit you cut out will be scrap, so you can probe this by drilling a hole to establish the thickness of the material. Once you know that you can use a circular saw to a mm less and use that to cut around the rotten section, Then a Worx type vibrating saw/multi-tool to deal with the 1 mm. I think you can get a small plunge circular saws specifically designed for this type of job.

Thanks again for your suggestions

 

I think I know what you mean by access trap - a section you can lift to access/inspect the bilge, right? To be honest the one at the back end of the cabin is just a section of substrate cut out, and not really secured at all, you just kind of pop it in and out as best you can(!) 

 

I'm guessing by securing something to support the edges you mean something above the substrate (and below the floorboards on top of it)? Doable, I suppose, but tricky in that it would mean reducing the thickness of the floorboards to accommodate the fixing, I think? 

One of the things I'm wondering about is how bad it would be just to do nothing except put the floor back and give it time. Would that be asking for trouble?! 

[Tony Brooks]

1 hour ago, captain flint said:

Thanks again for your suggestions

 

I think I know what you mean by access trap - a section you can lift to access/inspect the bilge, right? To be honest the one at the back end of the cabin is just a section of substrate cut out, and not really secured at all, you just kind of pop it in and out as best you can(!) 

 

I'm guessing by securing something to support the edges you mean something above the substrate (and below the floorboards on top of it)? Doable, I suppose, but tricky in that it would mean reducing the thickness of the floorboards to accommodate the fixing, I think? 

One of the things I'm wondering about is how bad it would be just to do nothing except put the floor back and give it time. Would that be asking for trouble?! 

 

There is usually a gap between the bottom of the floor boarding and the top of the ballast that will allow you to fit a length of timber or metal around the edge of the hole onto the bottom of the existing floor boards, extending into the "hole" so the new section of the board has something to sit on. You will need more than one section for the run that passes over the bearers. I usually use timber glued and screwed from above, with the screw heads in countersunk holes.

 

Depending upon how the bearers run and their location in respect of the hole you might find it satisfactory just to drop a new piece of board into the hole so it rests on the bearers, but when you walk on it the edges may well flex

 

I don't really understand the bit about putting the floor back down unless what you actually walk on is some sort of decorative finish that sits on the actual floor boarding, and if it is I think it depends on how permeable it is. If it is not then any residual damp can't escape, so putting the "floor" back down might not be such a good idea until you are sure all the damp has gone. (I am not commenting upon the damp meter reading). If it is permeable, then any residual damp can still escape into the boat. I tried to indicate that letting it dry out and if necessary treating any mould may be the best option.
 

[captain flint]

It's wooden floorboards laid on top of the actual board. So yes, decorative, basically. Not very permeable. I'm going to leave them off for it to dry out, then put them down when dry. 

 

The top side of the actual board is pretty wet but it's evidently still damp underneath. 

 

I already treated the mould on the top, which was not extensive anyway.

 

Do you have any suggestions for treating any mould underneath the floor?? Can't think how one would do that*

 

*(without removing the board, at which point I think I would just go ahead and replace it with ply as per your helpful suggestion. I'm currently thinking I won't do that now, and see how it goes. That can always been done later if it's really necessary, but the board looks and sounds structurally sound so right now that would feel a bit premature and pessimistic. Fingers crossed). 

 

Thanks again

[Tony Brooks]

24 minutes ago, captain flint said:

It's wooden floorboards laid on top of the actual board. So yes, decorative, basically. Not very permeable. I'm going to leave them off for it to dry out, then put them down when dry. 

 

The top side of the actual board is pretty wet but it's evidently still damp underneath. 

 

I already treated the mould on the top, which was not extensive anyway.

 

Do you have any suggestions for treating any mould underneath the floor?? Can't think how one would do that*

 

*(without removing the board, at which point I think I would just go ahead and replace it with ply as per your helpful suggestion. I'm currently thinking I won't do that now, and see how it goes. That can always been done later if it's really necessary, but the board looks and sounds structurally sound so right now that would feel a bit premature and pessimistic. Fingers crossed). 

 

Thanks again

 

No idea how to treat any mould under the floor apart from drilling a load of small (2mm?) holes nearly all the way through the board and flooding them with whatever anti-mould/anti-rot liquid you have already used.

 

If it is mould and not rot mycelium, then once the whole lot dries out I would hope that it would die. Happy for our more knowledgeable members to say different though.

[Tracy D'arth]

I don't think rot mycelium will grow on OSB due to the resin it is made with.

When it dries out I would expect it to be OK to leave in situ. It will take months of dry warm weather to fully dry out even if ventilated.

To find the angle irons underneath you could try a very strong magnet, neodymium, but if the boards are on timber cross bearers as they usually are then it may be too big a distance. But you may find the screw heads this way.

In my view, modern marine ply is worse than OSB for strength, durability and cost.

[Tony Brooks]

1 hour ago, Tracy D'arth said:

n my view, modern marine ply is worse than OSB for strength, durability and cost.

 

 

I second that, providing it is quality OSB3 or better. No voids that I have ever seen, lots in much modern so-called marine ply, and no areas where the adhesive between plies is missing.

[captain flint]

On 24/02/2024 at 16:23, Tony Brooks said:

 

 

I second that, providing it is quality OSB3 or better. No voids that I have ever seen, lots in much modern so-called marine ply, and no areas where the adhesive between plies is missing.

 

Thanks Tony and Tracy, nice hear, though I'm slightly scratching my head simply because it's so hydroscipic, I can't help but feel if the same situation I had faced had occurred on decent ply it would have been far easier to sort out? But that's very interesting re rot mycelium not looking the resin. I must say that, structurally, the OSB seems perfectly sound despite everything. 

 

When it comes to the mould, I've  messaged to stick an endoscope camera down there. Tricky business, but I could just about see that while there are plenty of spots of black mould, they're very small, and it's localised. I figure it's not that advanced, it's under the floor, and hopefully will eventually dry out. Currently quite well ventilated but harder to keep it that way once the floorboards that are laid on top of the osb are replaced. Then again it was a bone dry bilge once so with a bit of luck it can be again. 

 

I'm going to keep the floorboards up for another 10 weeks or so and see how dry it is by then. It's quite disruptive though. At some point they will go back and I will just have to monitor things for musty smells etc. If absolutely necessary, they can always be taken up again and a more drastic solution sought at that point.