Quarry Tile Floor.......damp membrane

[aspley]

Am doing up a 150year old farmhouse which has old quarry tiled floors . The tiles are solid but in poor visual nick having been laid 100years ago.

Question is....to save digging up the floors to 12" or so, would I get away with a polythene membrane and 3"screed reinforced with glass fibre to provide a damp proofed and flatter floor??

 

[Softus]

I don't understand - are you proposing to increase the height of the floor by 3"? Or dig down 3"?

Bear in mind that in attempting to prevent damp coming up you might create more problems than you solve. Any DPM that you install has to be contiguous with the wall DPC, otherwise the damp you're trying to keep down will rise up in the joint between slab and wall.

I would address this by digging down to at least one course below DPC, and installing the membrane by sticking it with bitumen paint to that brick course (or courses). This dictates the minimum height for your dig, which in practical terms might mean you have to go deeper in order to cast a thick enough slab before you screed.

 

[aspley]

Thanks for your interest.

I am unashamedly trying for a short cut by screeding over what is there.
The height is not an issue as all the old wooden door lintels are coming out and it's easy to take a course of brickwork out at the same time.

I am really just trying to avoid that 12" dig and concrete laying task.

The building does have a slate damp course and the final level of the screed would remain below that.

What do you think.....I have seen your posts elsewhere and would welcome your well reasoned opinion.

 

[Softus]

I am unashamedly trying for a short cut by screeding over what is there.

I respect your honesty.

You're only human, and I've been faced with this dilemma myself.

The height is not an issue as all the old wooden door lintels are coming out and it's easy to take a course of brickwork out at the same time.

This part has confused me - what would removing a brick course achieve?

I am really just trying to avoid that 12" dig and concrete laying task.

All I can say is that each time that I've bitten the bullet, I've been glad afterwards that I did. If you're in task avoidance mode, and we all do it from time to time, then you're not making any decision for the right reason. Obviously it's better to do less work, but not at the cost of doing the job right.

The building does have a slate damp course and the final level of the screed would remain below that.

This leads me to ask you: what are the symptoms of the problem that you're really trying to solve?

 

[aspley]

Removing the course of brickwork above the old door frames would allow me to raise the doors a tad to compensate for 3"screed.

The floor does not have a damp membrane. The tiles are laid on old ash and sand as far as I can tell. I just felt a damp course would be a good idea .

 

[Softus]

Removing the course of brickwork above the old door frames would allow me to raise the doors a tad to compensate for 3"screed.

Ah - I get it now. Sorry to have been thick about it.

The floor does not have a damp membrane. The tiles are laid on old ash and sand as far as I can tell. I just felt a damp course would be a good idea .

I would be sorely tempted to leave things as they are. If you suspect an increasing damp problem then this is more likely to be down to factors outside the house rather than underneath, but the only problem is a cosmetic one then I wouldn't dig, and I wouldn't screed it.

As detailed earlier, then only proper remedy to a lack of a conventional concrete/DPM/screed base is to provide one - you can't just introduce the top layer and get away with it.

The problem with a 3" screed is that wouldn't be strong enough without a substantial raft underneath, and any 'tectonic' movement, as might occur in a very old house, could easily fracture it - then you'll have more problems than you started with.

Sorry to be the one throwing cold water over your plans, but it would pain me to think of you gaily screeding and tiling and then regretting it in a few months time.