Moisture appearing on floorboards near fire hearth

[Phoenixfc7]

Hi

Having had a new hearth fitted and about to get carpets put in I'm worried about the cause behind this water appearing through the floor boards. Basically I had to dig up the old concrete hearth and took a few bags of soil type stuff up and then refilled with broken bricks and sand with a new concrete base. Then the hearth was fitted a good few weeks after. That was about 3 months ago and now the carpets will be going in I noticed after shifting things out that the floorboards appear to be drawing water. My concern is that it's drawing from the ground due to the soil base I came across as I would assume it would have dried by now. Any help gratefully received. Thanks

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• Phoenixfc7
• 4 Sep 2013
• 1

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• Phoenixfc7
• 4 Sep 2013
• 1

 

[Phoenixfc7]

Here's the pics I hope!

 

[big-all]

i assume the floor boards are extremely dusty as the the differential looks extreme
concrete can take 6 months to dry out dependent on thickness

if there is a connection between the hearth and the ground you must have a dpm to stop moisture transference

if the floor is dusty please wash/mop it clean and take another picture

 

[dann09]

I agree with big-all.

In pic no 2 are the boards landing on a joist thats running parallel with the hearth (a trimmer)?

What is the black thing or stuff thats peeping out from under the hearth?

 

[mattysupra]

i assume the floor boards are extremely dusty as the the differential looks extreme
concrete can take 6 months to dry out dependent on thickness

Can take a a lot longer than that. 6 months is a average for a concrete subfloor that is approx 4" deep.

Concrete drying calculation is 1mm per day up to 50mm deep. Over 50mm deep it is 1/2mm per day .

This is calculated at a 55% rh moisture level and at 21c.

If the concrete has been covered up with a fireplace then it will takes years to dry. This also all depends on if you installed a dpm sheet under it.

As imple fix for this is to cut the concrete back and a barrier put in place between the floorboards and the concrete other wise they will soon be rotten.

 

[Phoenixfc7]

to answer the questions
the black stuff I assume is the grout that the guy who fit the hearth used.
The boards do sit on a joist that runs across the front of the hearth right up to the base the hearth is sat on.
The concrete is aprox 2-3 inch thick and it appeared dry before the hearth was put down. Last night I sanded the area and cleaned it and these are the pics.

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• Phoenixfc7
• 5 Sep 2013
• 1

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• Phoenixfc7
• 5 Sep 2013
• 1

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• Phoenixfc7
• 5 Sep 2013
• 1

 

[dann09]

A couple of things:
the hearth should not sit on any wood, but if the hearth extends more than 300mm off the face of the c/breast then it should be safe if not strictly legal.

And, as above, the trimming joist should be masked from any masonry contact with a Membrane (DPM). Perhaps, you can slip some membrane in from above or below the floor. Lightly prise the T&G ends up to provide an access gap.

If, from below floor, you cant get a bit of membrane behind the joist to separate it from the masonry, then leave it - the joist will probably outlast your occupancy.

Traditionally, a wood "margin" to finish and cover the T&G was fixed around, and butted up to, the constructional hearth.

It looks like it will be an excellent bit of work when finished. Well done.

 

[Phoenixfc7]

Hi

Thanks for the advice. The hearth is not sitting on top of any wood, it is sat on top of the concrete base which you can still see a couple of inches of before the floor boards butt up to it. It sounds like its just drying out and once that fire is going I am sure it will dry out quicker! I will do as you suggest and pride the floor board up and try and slide in a membrane hopefully in between the joist too.