Help please - dry mix queries. - Dry mix as base layer, first project

[The Not So Handy Man]

Hello,

New Build, onto of an Old Cement Works Factory place...
Ground appears solid, Found lots of stones, chalk and alsorts.
First DIY project i have done without the help of my DIY expert old man...

Proper DIY job I'm completing in my garden.
Large Patio area, Approx 20m2 in a Abnormal shape. its an 'L' shape but instead of a 90 degree turn its wider.

After speaking with my DIY expert Father (30 odd years of trial and error around his own house), he said that the ground seems solid enough and that if i was to compact a dry mix layer down and then sharp sand ontop, it should be strong enough for the 600mm x 600mm x 20mm porcelian Slabs i'm putting down.

I started by digging out down a fair amount so that the level points away from the house. Compacted the soil down till i couldn't see my foot prints when i walked over it.

Next i started laying a dry mix, of 3:1 (Sharp Sand, Cement) and compacted this down.

Here's my problem. I ran out of time and didn't fully complete the dry mix layer, and the whacker plate i hired has now gone, i need to hire it again to finish of my dry mix layer.

The Dry mix that i have put down is now a week old, it has gone solid and im not worried about the strength of it, if i was to wet the week old dry mix first can i put more dry mix ontop of it and compact it down? Or will there be issues with the old and new dry mix bonding together?

I understand this is not a professional job by far, i accept any insults based on the 'proper' DIY job i've done. I just need to know if i can put a new dry mix (3:1 sharp sand:cement) ontop of an already half cured dry mix without issues in the next 5 - 10 years.

If i should use a bonding agent, can anyone recommend one? im from the UK.

[Tony McC]

I'm struggling to follow this build-up.

Why the dry mix? Why not a proper sub-base?

Are you really planning to lay porcelain onto sand?

Sounds like a recipe for disaster to me!

[The Not So Handy Man]

It started with my dad telling me that I don’t need sub base.

The ground workers that put the existing patio down had installed it with a dry mix, so those were the reasons.

And yes really planning on laying porcelain onto sand!

Could you provide any advice? Will the new dry mix bond with the old dry mix? Or should I use some form of bonding agent?

What is the problem with laying porcelain onto sand? The company say that you can lay them on sand?

[The Not So Handy Man]

These are the slabs I am getting! They say you can ly them on near enough anything:
https://www.toppstiles.co.uk/eversca....0Square

I understand they may sink after a little while but I don’t mind lifting them up and putting more sand under to bring them back up.

Do you think this build up will last at least 5-8 years?

[The Not So Handy Man]

Any advice regarding laying new dry mix on old dry mix is highly appreciated and why you don’t think I should lay the slabs on sand? Have you known anyone to lay them on sand? Have they had problems

[Tony McC]

5-8 years? You'll do well to get 5-8 weeks!

While you could lay on sand (laying on gravel to counter frost heave is common in Europe - read this page) you have to accept that it WILL move and start to look somewhat higgledy-piggledy. That's not what we normally expect in Britain and Ireland where our maritime climate protects us from forst heave, so we expect our paving to stay put.

How do you think that sand bed will behave in the sort of torrenbtial downpours we've had over the last couple of weks? Or through a winter inundation?

Once they start to move, there is a significant risk of chipping and spalling to the arisses, and they can start to rock or become loose, drift out of alignment.

Would you lay your kitchen floor tiling on sand?

You can choose to lay them on a bed of feather if you wish, but the accepted methodology for installing porcelain paving in Britain and Ireland is either a full mortar bed or an outdoor grade adhesive over a concrete base.

And I wouldn't be taking pavement construction advice from a floor tile retailer!

[The Not So Handy Man]

Right so my main worry is that during heavy rain the sand will likely flow away? Can that be stopped by using kiln dried sand in the joints? Such as with block paving? Because the kiln dried sand helps add a lot of strength to block paving from what I’ve read online. The concrete base will mean the sand can’t really go anywhere? Have you seen or do you know anyone that has land porcelain slabs on sand ontop of a concrete base with kiln sand within the joints? Or is this all education/experience you are giving this advice from?

[Tony McC]

Sand in the joints will, not surprisingly, not prevent sand from the bed being washed out in heavy rain.

While KDS adds strength via the very narrow joints of a block pavement, it does not behave in the same way with porcelain paving. Completely different materials and completely different construction methods.

I *have* seen a porcelain patio laid on sand and I told the guy responsible he was feckin' eejit, in front of the customer he was trying to rob of good money for appallingly shoddy work.

Not sure what you mean about "education/experience". I've spent, so far, over 50 years in the paving trade. You can choose to listen or you can ignore me. You decide. I haven't the time to deal with this level of nonsense.

[The Not So Handy Man]

No need to be rude. I’m inexperienced and just asking questions because I couldn’t find anything online.

I am going to lay the slabs on a mortar bed as per your advice.

Thanks for your help

[MikeG]

All the information you need to lay a porcelain patio is on this website.

[The Not So Handy Man]

This started with questions about dry mix and turned into questions about porcelain.

Turns out I just put more dry mix ontop and it worked well. So incase anyone else has the same problem, you can put an inch of dry mix cement on old dry mix and it works fine. Just make it a strong mix.

[MikeG]

The two layers will have gone off as just that. I would hold fire a little bit before telling others it’s fine to do so. There are ways it should be done and for good reason. You must realise you are asking for advice on how to do it not properly? It’s your patio and you can do it how you want, but I assume you wanted a professional opinion?

[The Not So Handy Man]

I would love a professional opinion on how to lay new dry mix concrete ontop of old dry mix concrete, that is the whole reason I cane to this forum. But no one has told me the proper way of doing it. Could you tell me how?