Yet another bodge job

[Mjward]

A few years ago a bought a veritable house of horrors. The latest finding, I was reapplying the patio grout the other day and no matter how much I put in, it just disappeared below.

"no, surely not, they didn't did they?"

They did.

Lifted up a few slabs and realised my patio structure is a few joists (not enough) with 18mm plywood (not marine grade) sheets on top, followed by dot & dab (not enough) adhesive for the patio itself. Unsurprisingly the ply was basically now like cardboard and the reason why the grout failed to find a home in a few places is where the ply had disappeared and there was nothing beneath.

So....

I've got too many projects on to give this a "proper" treatment so I'm working out the best bodge for a bodge and will deal properly at a later date.

My thoughts are...

(1) Check joists are sound/replace where needed
(2) replace all plywood
(3) drill a handful of drainage holes in ply
(4) treat plywood (inc edges) with yacht varnish
(5) re-lay patio

My logic is, with properly maintained grout, the volume of water getting to the ply should be minimal. What gets there should sit on the varnish until it either evaporates or builds up enough to find it's way to a drainage hole. Given the current setup lasted 13 years, I'm confident this bodge should get me through to when I can treat properly.

Question for you smart minds, with an economical hat on, what would you do differently?

TIA

 

[ChaiLatte]

What is the ventilation like to the underside? That will determine structural happiness.

I would consider adding 2a to your list: tile backer board (cement board). Alternatively, a wet room tanking membrane or slurry.

E.g. https://pureadhesion.co.uk/mira-tanking-kit-full-wet-room-solution/

You can probably build your own kit cheaper by buying a standard tanking slurry and buying the fabric separately (Selco have it in the roofing section). The primer is just SBR. If corners are needed, pre formed ones are not necessary; they can be folded origami-style yourself.

If you drill drainage holes, can you sleeve them with a plastic pipe that extends below the bottom of the plywood and seal the entry? Then the plywood should never see any water, only humidity from below, which ventilation will deal with.

 

[ChaiLatte]

Another slightly different option might be to waterproof the plywood properly (like a GRP flat roof), make sure it has a fall to shed water and then lay the slabs on plastic/rubber pads at each corner. This is how you would do a roof garden. Clearly, you have to restrain the slabs at the perimeter.

In effect, what you are doing is creating a very low headroom roof, with access on top of it.

In the post above, what you are doing is creating a tiled, suspended bathroom floor, where the 'ground floor' below has a low ceiling height.

 

[Bingy man]

No 5 . Leave it as is and rip the whole patio up when you have the time . No point spending money on a job that has been bodged , no doubt there will be other horrors so just let it be . Blobs , spots , dot and dab is pants as it leaves voids under the slabs for water to hold and freeze in the winter months. However unless I’ve miss read your post-why would slabs be laid on joists and plywood ? Is this patio internal ? or is just too early lol

 

[Phil Pascoe]

Move house.

 

[thetyreman]

can we see photos? is it outdoors or inside? I was going to suggest sand to lay the slabs on but that presumes that it's outdoors.

 

[paulrbarnard]

I’m with Phil on this one…

 

[Mjward]

What is the ventilation like to the underside? That will determine structural happiness.

I would consider adding 2a to your list: tile backer board (cement board). Alternatively, a wet room tanking membrane or slurry.

E.g. https://pureadhesion.co.uk/mira-tanking-kit-full-wet-room-solution/

You can probably build your own kit cheaper by buying a standard tanking slurry and buying the fabric separately (Selco have it in the roofing section). The primer is just SBR. If corners are needed, pre formed ones are not necessary; they can be folded origami-style yourself.

If you drill drainage holes, can you sleeve them with a plastic pipe that extends below the bottom of the plywood and seal the entry? Then the plywood should never see any water, only humidity from below, which ventilation will deal with.

Significant ventilation, ergo the reason I think the builders opted for this method. It was an extension where the floor is between 0.5-1m above (sloping) ground level.

So definitely optionality to sleeve and seal and ventilation is so good there is wildlife living under it

I did my bathroom last year so have a bit of familiarity with cement boards and tanking, was thinking varnish would suffice given how little water it will get but for the incremental coat maybe you're onto something with tanking.

 

[Mjward]

No 5 . Leave it as is and rip the whole patio up when you have the time . No point spending money on a job that has been bodged , no doubt there will be other horrors so just let it be . Blobs , spots , dot and dab is pants as it leaves voids under the slabs for water to hold and freeze in the winter months. However unless I’ve miss read your post-why would slabs be laid on joists and plywood ? Is this patio internal ? or is just too early lol

Rather than the original builders use cement or anything else to fill the gap, they've raised the external patio on joists to meet the ground floor level of the main house (this was all part of an extension 15 years back).

The joists are actually sound/dry but in lifting a handful of patio slabs to see underneath I took the lump hammer to the existing ply to see it's (lack of) structural integrity. That said, I'm knocking it as it's not the way I would have done it but it's lasted 15 years and only failing in places.

 

[Stigmorgan]

Option 6, remove the tiles/slabs and put decking boards down instead

 

[Mjward]

can we see photos? is it outdoors or inside? I was going to suggest sand to lay the slabs on but that presumes that it's outdoors.

It's outdoors BUT... Very very difficult to gain access on anything but foot. It's a dog leg stair case down from the road level. That said, it was done when the extension was built ie at that time the builders could have done it properly but now the extension blocks off vehicle access to the patio at the low level.

 

[Mjward]

Option 6, remove the tiles/slabs and put decking boards down instead

That's actually not a bad shout. I've just replaced a large area of decking so would weather nicely together.

 

[Mjward]

Pic for ref

 

[Stigmorgan]

That's actually not a bad shout. I've just replaced a large area of decking so would weather nicely together.

I do occasionally have good ideas just don't tell SWMBO

 

[Mjward]

I do occasionally have good ideas just don't tell SWMBO

My lips are sealed!

 

[Bingy man]

Rather than the original builders use cement or anything else to fill the gap, they've raised the external patio on joists to meet the ground floor level of the main house (this was all part of an extension 15 years back).

The joists are actually sound/dry but in lifting a handful of patio slabs to see underneath I took the lump hammer to the existing ply to see it's (lack of) structural integrity. That said, I'm knocking it as it's not the way I would have done it but it's lasted 15 years and only failing in places.

So I assume they could ( should ) of used hardcore to build up level , then then dry mix sharp sand / cement, I think it more luck than judgement that joists have lasted that long - I think the plywood has helped to protect joists but it sounds like they were next to fail .. if you go the decking route be wary of composite decking as it’s not as good as they make it sound .

 

[Mjward]

So I assume they could ( should ) of used hardcore to build up level , then then dry mix sharp sand / cement, I think it more luck than judgement that joists have lasted that long - I think the plywood has helped to protect joists but it sounds like they were next to fail .. if you go the decking route be wary of composite decking as it’s not as good as they make it sound .

Think what has saved it is the builders seem to be more knowledgeable about timber than the other building materials. They've kept the main structural joists away from the floor/soil. That and 15 years of I assume fairly good patio grout maintenance has kept water ingress to a minimum.

On a side note, what are the negatives of composite decking?

I replaced like-for-like timber decking solely to keep costs down but had only read positives about composite (other than the price)

 

[Morag Jones]

I bit the bullet 3 years ago and replaced a wooden deck with composite. Yes, it was outrageously expensive but that pain has passed, it looks fabulous and I have no regrets. But I have one thing I wish I had done.

As you see, we have unusual pets…. They are generous with little messages. Hence there’s a lot of sweeping/washing, once or twice a day. 365. This is why the plastic works so well for us as it doesn’t get algae or need treating.

As there is a high proportion of wood particle in the board for stability (with 2mm plastic decorative finish on top), any exposed end grain does take in some water. I’ve had some swelling at the ends where the water runs off.

I wish I had sealed these ends, have mused that CPES would have done the job. The planter is WIP and will report on success or otherwise.

We used to have a low fence around the deck, but they are birds!

 

[Bingy man]

Think what has saved it is the builders seem to be more knowledgeable about timber than the other building materials. They've kept the main structural joists away from the floor/soil. That and 15 years of I assume fairly good patio grout maintenance has kept water ingress to a minimum.

On a side note, what are the negatives of composite decking?

I replaced like-for-like timber decking solely to keep costs down but had only read positives about composite (other than the price)

The biggest issue when I researched composite decking was the subframe has to be designed for composite ( the distance centre to centre is less than timber ,, so it’s not as simple as replacing timber for composite without re designing the subframe , raised decks have to be installed with solid composite ( even more expensive) an air gap of 75 mm is required. If your composite deck boards are shorter than your deck width ( 3.6 boards but a 5 mtr width) then where the 2 boards meet you need a double joist ( more cost ) you then have to leave an expansion gap . Different expansion gaps end to end and lateral gaps between the boards depends on the outside temperature when installing them. The boards ( I’m not saying all ) are prone to splitting and cracking and shrinking and fading due to the effects of the weather changes. Although it’s resistant to rotting it’s susceptible to mould and mildew especially in shaded areas. So apart from the extreme cost and the installation requirements the advantages ( imo) don’t justify this cost . I’m removing a large deck + a smaller one later this year - install cost was approximately £8,000 and it’s suffered all of the above + damage to the corners and end panels and although it’s probably an extreme example it shows what can happen if not installed correctly.. I much prefer traditional timber decking and a regular maintenance regime ( cleaning and painting/ or oiling etc ..

 

[Bingy man]

I bit the bullet 3 years ago and replaced a wooden deck with composite. Yes, it was outrageously expensive but that pain has passed, it looks fabulous and I have no regrets. But I have one thing I wish I had done.

View attachment 185583

As you see, we have unusual pets…. They are generous with little messages. Hence there’s a lot of sweeping/washing, once or twice a day. 365. This is why the plastic works so well for us as it doesn’t get algae or need treating.

As there is a high proportion of wood particle in the board for stability (with 2mm plastic decorative finish on top), any exposed end grain does take in some water. I’ve had some swelling at the ends where the water runs off.

I wish I had sealed these ends, have mused that CPES would have done the job. The planter is WIP and will report on success or otherwise.

We used to have a low fence around the deck, but they are birds!

I actually like the choice of colours and designs of composite boards and overall yours looks stunning and just by your photo I can see that you take good care of it . If possible you should address the ends that you mentioned suffer from swelling before it’s beyond repair..