Outdoor patio base options

[AverageDIYerEssex]

Hi all. Wanted to get peoples advice on my next project. So I have some bifolds with 600x600x8mm tiles inside and plan on putting the same tiles outside so it flows. Currently there are big standard outdoor slabs not cemented down as pictured.

My initial plan was to take all the existing slabs up, build several wooded frames and then hardcore and cement them to make a long base and then standard tile on top of that.

However other friends and family have got my brain thinking about other, and maybe easier options and wondered what your opinions are or advice on how best to do it.

Suggestions included building a wooden base with joists etc and then over boarding it and tiling on that. Another was pouring the big concrete slabs on top of the existing slabs laid on the floor.

Really any advice welcomed. Thank you.

 

[Nintendofan]

are your current tiles inside slip resistant when wet?

 

[AverageDIYerEssex]

are your current tiles inside slip resistant when wet?

Hi. They are to a degree but not the best for outdoors. However I have found a couple of products to treat them to make them better. To be fair I've walked on them with wet feet indoors and their surprisingly unslippery

 

[Nintendofan]

Hi. They are to a degree but not the best for outdoors. However I have found a couple of products to treat them to make them better. To be fair I've walked on them with wet feet indoors and their surprisingly unslippery

now add a bit of algea/moss and loose leaves over the winter and tell me they're still not that slippy

 

[AverageDIYerEssex]

now add a bit of algea/moss and loose leaves over the winter and tell me they're still not that slippy

I appreciate what you're saying however I am asking for advice on the foundations of which to lay them not on how slippery they'll be in winter.

 

[yorksbuilder]

Some questions:
1. What level do you want the finished outdoor patio to be?
2. Does your lawn slope towards the house, away from, or is it flat?
3. Where is your DPC located in the brick wall?

 

[AverageDIYerEssex]

Some questions:
1. What level do you want the finished outdoor patio to be?
2. Does your lawn slope towards the house, away from, or is it flat?
3. Where is your DPC located in the brick wall?

Hi and thanks for your reply.

1. Pretty much level with the top of the bifold cill so around 150-180mm (I have loads of hardcore and blocks left over from demolishing the hole for the bifolds I could make use of)

2. It's pretty much flat but plan of re-landscaping it afterwards and returning so could do something with it then if needed.

3. The DPM would be lower than this level I believe. However I wasn't planning on going all the way to the house because do the air bricks etc so was going to leave a 100mm gap between the new base and the the house to a) allow some air into the air bricks (I was thinking I would also run a pipe through the new base to the front to allow RW tea air to flow towards the air brick if that makes sense. And also to allow any water that drains from the window cill outlets (underneath the cill) to go into this 'gulley'. There is a drain pipe each end of the the house so could potential direct anything Into that too.

 

[yorksbuilder]

Building regs state that you need to have min of 150mm between the patio and the DPC. If you bridge it you will have damp issues inside the house, and if you build higher than it, even leaving a small gap you may have questions during survey if you sell the house.. (which you can deal with but separate subject)

If you really want a level-as-possible transition from inside to out , i would build an aco-drain along under the lip of the bifoild threshold cill, so any rain running off there will flow in to the drain. Then plumb the slot drain into a combined sewer or properly build soakaway
For the small gap between the drain and the house wall, you canlay concrete along the base of this, and slope it sideways to remove any water out from there, or run some 50mm pipe transverse to the house to take any water away from the house

then take up paving slabs
inspect the old base
remove if its bad (soil, weeds, worms etc)
place new sub base (plus weed membrane if you want)
100mm crushed stone sub base
100mm concrete slab on top of this, finished with powerfloat to the tile thickness Plus tile adhesive thickness depth below the aco drain at your threshold.

Slope the slab away from your house at 1:80 slope

I highly recommend not using the internal tiles, (not all are suitable for outdoor), and using proper non slip outdoor 20mm thick porcelain tiles

 

[yorksbuilder]

Guidance for the construction method of slot drain: https://www.pavingexpert.com/dpc01#workarounds

 

[mrrusty]

Using interior style tiles outside fixed with normal cement-based tile adhesive is perfectly possible provided they are designed to be totally frostproof. However, there is another factor in play and that is expansion and contraction of the concrete slab and the tiles. Outside the potential temperature range (summer winter) is going to be higher than inside, so any differential expansion between the concrete and the tiles could cause cracking. My very quick calc over a 30 degree temp range gives an expansion differential of ~0.5mm over a 6m distance between typical ceramic tile (0.007 mm/deg/m) and typical concrete (0.01 mm/deg/m) - not much, but perhaps enough to take in to account.

I have used 600x600 porcelain in a small inside/outside patio area 3m x 3m exposed to frost (about 30 degree temp range) over a concrete pad and I used Ditra uncoupling membrane. 5 years on and it's solid - no cracking.

 

[AverageDIYerEssex]

Thank you so so much for such helpful and informative replies. This is exactly the help I wanted thank you.

I will be re-reading it over and over to fully understand it this evening lol.

I don't actually know where abouts the DPC is on my house, I cannot see it sticking out like you sometimes can. Potentially where the normal bricks change to block work? I'm not sure. I have this pic from when the opening was made and there is DPC in that place on the inside course as pictures.

Another quick Q which will help me digest it tonight... if I am only having the patio and sub base against the house directly below and/adjacent to the opening for the bifolds... is it as important regarding the DPC levels as there is nothing above it for damp to rise to? Do I make sense? As in there is no bricks as it's the opening and bifolds above that join. Just a thought I've had.

 

[AverageDIYerEssex]

Regarding the arco drain, I was planning on doing something like this in an earlier plan. Would it be suitable to plumb this into the drainpipes that come down either side of the opening from the roof? It will all be the same rain water

 

[yorksbuilder]

Another quick Q which will help me digest it tonight... if I am only having the patio and sub base against the house directly below and/adjacent to the opening for the bifolds... is it as important regarding the DPC levels as there is nothing above it for damp to rise to? Do I make sense? As in there is no bricks as it's the opening and bifolds above that join. Just a thought I've had.

Yes you make sense. Yes it's as important as moisture if trapped behind the patio can be absorbed along your wall and not just up it

 

[yorksbuilder]

Would it be suitable to plumb this into the drainpipes that come down either side of the opening from the roof? It will all be the same rain water

Yes you could, as long as it ends up draining to a proper rainwater gulley

 

[AverageDIYerEssex]

Thanks again for your help. So I've had the crayons out and knocked this up and hoping it's incorporated what you suggested to some extent. The 'empty channel' is where I could lay the arco falling from the centre running sideways and into the drainpipes at either side of the bifolds.

I was planning on having the tiles sitting slightly above the cill going halfway up it as picture.

Am I on the right lines?