Flagstone floorboard junction

[Samantha L]

Hi All,

I’ve just given our kitchen a mini makeover (will be changing it completely when funds allow) and just took up a manky bit of carpet we inherited and found where the wooden floor meets the flagstones under the oven is rotten. In places and gaps have been filled with expanding foam. This area of the kitchen is pretty damp due to high ground levels externally (again something to be remedied in the future). We’ll replace this floorboard but given the flagstone seems to either attract moisture due to salts present, or moisture passing through I’m not sure how to prevent this happening again, or at least limit the wood rotting quickly. Is it just a case of treating the replacement board or any other suggestions? Thanks in advance

 

[Cubist]

I think theres a more likely source of damp in that kitchen which might also explain why there was a carpet and how it came to be so manky. If that is a fan oven it's unlikely to have an extractor, for obvious reasons. The oven can during the cook and subsequent cooling stages produce large quantities of moisture laden air that condenses out on the door panel and from there runs down to drip onto the floor below. It would be easy for you to test this by justing putting a shallow dish of vegetable in to roast.

For the future though and to reduce damp transfer to the floorboard it would be sensible to scribe cut the edge of the board to provide a narrow air gap of say 5mm and before fixing the board you could perhaps also apply a little varnish to that edge too. However, if the source of the damp turns out to be condensation from the oven then an alternate solution may be needed.

BTW - have the joists below that floor been affected?

 

[Samantha L]

Hi @Cubist, thanks for your reply.

There’s currently no extraction in the kitchen. Hopefully something we can put in soon. Even the window by our sink has no opening, probably because of the depth of the sill and worktops. Would need pretty long arms to open it but I do wish there was the option! There’s a window on the other side though, so currently doing our best to keep it ventilated, especially when cooking. Agree it could be moisture from the oven condensing.

On the joists, possibly - but haven’t taken the floorboard up yet to check. There is a slight spring in that corner where the expanding foam is though, so quite likely! Plan is to move the kitchen to the other side of the room eventually, so I’m loathed to do too much right now as will be ripping it all out in the next couple of years.

 

[Kearn]

Really depends on what’s happening under there. I’ll assume the slabs are still directly on earth, they will wick up moisture from the ground, especially in this rainy weather, that’s normal and they need to be able to evaporate that moisture from their surfaces. However, you’ve got adjacent boards, assuming over a void with joists?

How does the slab area stop and the void begin?

Any timber against the slabs will always suck up moisture from the slabs, so a simple air gap works, but leaves a gap in your floor. Alternatively, twist up and wedge oakum into the gap to provide a traditional barrier.

 

[Flyfisher]

Totally agree. I suspect that expanding foam is doing a lot more harm than good and the first thing I'd do is remove it. The resulting air-gap might be all that's necessary to allow any moisture to naturally evaporate.

The second thing I'd do is to get some form of extraction into the kitchen area before its absence starts to cause other problems.

 

[Samantha L]

Really depends on what’s happening under there. I’ll assume the slabs are still directly on earth, they will wick up moisture from the ground, especially in this rainy weather, that’s normal and they need to be able to evaporate that moisture from their surfaces. However, you’ve got adjacent boards, assuming over a void with joists?

How does the slab area stop and the void begin?

Any timber against the slabs will always suck up moisture from the slabs, so a simple air gap works, but leaves a gap in your floor. Alternatively, twist up and wedge oakum into the gap to provide a traditional barrier.

Hi @Kearn. Not entirely sure if the slabs are on earth still or whether they were put on a bed of cement. I’ll find out when I lift the offending board. It’s definitely over a void with joists. We have some kind of vent pipe coming out of the ground outside on the other side of the wall. So I’m curious to see what’s going on under there.

 

[Samantha L]

Totally agree. I suspect that expanding foam is doing a lot more harm than good and the first thing I'd do is remove it. The resulting air-gap might be all that's necessary to allow any moisture to naturally evaporate.

The second thing I'd do is to get some form of extraction into the kitchen area before its absence starts to cause other problems.

Agreed @Flyfisher I should dig out that foam. Just a bit worried it might leave a nice entry point for if I do that before I’m ready to replace with a new board

Extraction is definitely high on my list of priorities. Will get it put in at the same time as one for the bathroom. We’ve already got issues with humidity on ground floor due to high ground levels externally and lots of cement pointing.

 

[Itchinfilth]

How long ago did you remove the carpet?
I have taken up lots of coverings over flags in our house and the flags were damp. Within a few days they were dry.
As a first, get rid of the expanding foam

 

[Samantha L]

How long ago did you remove the carpet?
I have taken up lots of coverings over flags in our house and the flags were damp. Within a few days they were dry.
As a first, get rid of the expanding foam

Hi @Itchinfilth. The carpet was only covering the floorboards, it’s was butted up against the flags covering the expanding foam.