Repairing this porch floor doorway

[Sparrowhawk]

The ****** who built this porch spanned the door opening with chipboard and then laid tiles on top. Over 10-20 years, water has rotted the chipboard ("helped" by installing the UPVC door back to front with it draining inwards), the floor sagged and the tiles have broken.

 

The rest of the floor is presumed laid on concrete, with old terracotta tiles with the white tiles laid on top.

 

What's the easiest way to repair this? I note that the DPC stops at the side, so I'm thinking:

• DPC across the inner and outer bricks
• Something to pack the height (tile?)
• floor levelling compound to bring it up to the top of the white tiles

and then we'll lay something new over the top

 

Better way? And what would you pack the gap with? 

 

 

 

 

And yes, the whole internal structure of this porch is built from MDF, and not the moisture resistant kind 🤦‍♂️

[JpManning]

Before packing and levelling I'd sort the door, because that's the root of it. If the frame drains inwards it'll rot whatever you put back. Get the door and cill refitted the right way round, with the drainage slots weeping out and a decent seal under the cill.

For the threshold, cut out all the rotten chipboard back to sound material and see what's actually underneath. If it's a gap over the cavity, lay a strip of DPC across the inner and outer leaf, lapped up behind where the frame sits, then build it up with engineering brick or a cut concrete paving slab bedded on mortar. I'd avoid timber or plastic packers in there, anything that holds or wicks water will give you the same problem again.

Levelling compound is fine for the last few millimetres, but it doesn't like going on thick over a joint or anything that flexes, so get a solid base first. Prime the old tiles with the compound maker's primer and check they're well bonded before you go over them.

While it's all open I'd swap that MDF for moisture resistant board or treated timber, otherwise you'll be doing this again in a few years.

[Spinny]

Probably outward opening french doors fitted the other way around so that they would open inwards (as you would normally want for a porch).

[Sparrowhawk]

37 minutes ago, Spinny said:

Probably outward opening french doors fitted the other way around so that they would open inwards (as you would normally want for a porch).

 

That's exactly what they did. I've drilled drain holes on the now-outward side a year ago which helped and (since taking the photos) sealed the inward side drain holes, so will see how they go. TBH they need replacing so this is a "tide us over for a few years" bodge on the doors - but I'd like the floor repair to last longer. 

 

2 hours ago, JpManning said:

For the threshold, cut out all the rotten chipboard back to sound material and see what's actually underneath. If it's a gap over the cavity, lay a strip of DPC across the inner and outer leaf, lapped up behind where the frame sits, then build it up with engineering brick or a cut concrete paving slab bedded on mortar. I'd avoid timber or plastic packers in there, anything that holds or wicks water will give you the same problem again.

 

Paving slabs, that's a great idea. Yes, all under the chipboard is two rows of brick with a cavity like this, so a matter of finding something the right thickness. So you don't fix the DPC down, you lay it and then mortar and then the paving slabs, and rely weight to hold it in place?

 

With inward opening doors there's always going to be water dripping off the bottom when we open them in the rain, wet boots coming in etc so I want to make this new floor as waterproof as I can.

[JpManning]

2 hours ago, Sparrowhawk said:

 

That's exactly what they did. I've drilled drain holes on the now-outward side a year ago which helped and (since taking the photos) sealed the inward side drain holes, so will see how they go. TBH they need replacing so this is a "tide us over for a few years" bodge on the doors - but I'd like the floor repair to last longer. 

 

 

Paving slabs, that's a great idea. Yes, all under the chipboard is two rows of brick with a cavity like this, so a matter of finding something the right thickness. So you don't fix the DPC down, you lay it and then mortar and then the paving slabs, and rely weight to hold it in place?

 

With inward opening doors there's always going to be water dripping off the bottom when we open them in the rain, wet boots coming in etc so I want to make this new floor as waterproof as I can.

 

Yes, the DPC sits loose. You lay it across the full width (spanning both leaves and the cavity), then bed mortar on top and set the slabs. The weight holds it; you do not nail or screw it down, because any puncture defeats the point.

Keep joints lapped properly and take the membrane up a little at the door threshold so water cannot track under the door edge. With inward opening doors you want a proper threshold detail too: continuous DPM/DPC into an upstand or welt under the threshold, and a sealed sill so driving rain and wet footwear cannot soak into the floor make up.

For a more waterproof finish once the base is solid, a liquid applied tanking or a bonded waterproof membrane over the slabs before tiles or vinyl is worth it. Avoid relying on the old chipboard again in that wet zone.

[Nickfromwales]

@Sparrowhawk  

 

Chop a load of bricks / mortar / other out from the gap, then pour 2-part fibrous SLC in to get a uniform working platform around 50mm below DPC. 
 

Then use black jack liquid DPM, 2-3 coats, across the cured SLC and up the sides etc, and leave to dry. 
 

Then more of the 2 part SLC to the required level.

 

Find some complimenting mosiacs and tile the gap back in.

 

Pub.