Refixing loose patio slab

[Merlin5]

I've lifted a patio slab that was rocking when stepped on and also had some broken pointing.

There's loose sand underneath which I've piled to one side and it was covering a bit of a cavity. I'm wondering whether to pat the sand back down and just put some large blobs of sand and cement mix in each corner?

Do I need sharp sand, building sand, or some other type of sand, and would you recommend mixing 4 parts sand to 1 part cement? That's what I've been seeing on YouTube videos. And 3 to 1 for mortar joints? I also want to fill a small hole in my front wall.next to the window frame.

How much sand and cement do you think I should buy? I'm going to go to builders depot they're normally pretty inexpensive.

I'll need a bucket. And I'll need a trowel but I don't know what size. And should I use a piece of old hose to smooth out new pointing or just fill the gaps around the slab and brush away excess?

 

[Merlin5]

tbh I don't know about the exact measurement but I will advise you to be careful when working near wet cement and not to get it on yourself or clothes as you can get pretty bad burns.

Burns? Didn't know that.

 

[Merlin5]

Blimey sadat, that's a bit scary. Will marigold washing up gloves do?

For underneath the slab mix 4 parts sharp sand to 1 part cement. Compact all of that sand so its nice and flat. Spread the cement mix all over the area where the slab is going to go and as deep as possible. Dont just put blobs in corner. With whats left over you could then poke that into your hole.

Thanks apg. Good idea to use what's left over for the hole. So, cover over the sandy area too. Not sure what you mean by as deep as possible unless you mean pack the cavity covered by the sand?

Do you think these will be enough for under the slab, the pointing and the hole in the wall? It doesn't say how many Kg in the sand bag.

https://www.diy.com/departments/tarmac-sharp-sand-large-bag/5030349012445_BQ.prd

https://www.diy.com/departments/blue-circle-multipurpose-cement-25kg-bag/35715_BQ.prd?rrec=true

 

[Merlin5]

I mean when you lay the cement mixture make sure its not just 1mm thin. Try and put a good amount down so the slab can bed in properly.

Yes a sinngle bag of sharp sand and a single bag of cement will be more than enough.

Awesome, thanks, I'll get those tomorrow.
I'm also going to buy a 26 litre gorilla tub, it's one of those very flexible mixing buckets that should make it easier to clean away dried cement.
A gauging trowel and maybe a tuck pointer unless I can find something at home to bed the pointing mortar in place.

 

[Merlin5]

Normal it's the cut 5 gloves like these: https://www.screwfix.com/c/safety-workwear/work-gloves/cat850338?glovecutrating=cut_level_5 but I think the marigold should be fine as long as you don't make contact with bare skin and your skin is sensitive.

Also make sure not to get it on your clothes especially in the knees area when you are kneeling down.

Thanks, I'll use my old marigolds. Saw a video where a guy was handling a sand and cement wet mix, although a fairly dry wet mix, with thin nitrile type gloves.

 

[Merlin5]

Op... Dig out about half and inch of all the old sand and remove any cement from the edges of the other tiles.

Get one bag cement and one bag builders/sharp sand (no gravel in it) Make up a mix of 1 part cement to 3-4 parts cement. No water...

Put the new mix down level and flat. (piling in corners creates a vacuum under the slab and will crack it) place the tile on sand and using a small level to make it accurate.

Using a slightly strong 50/50 mix of sand and cement and pack it into the gaps evenly around the edges.

You can leave it after that, the moisture in the air with eventually set it in place. However the packing of the sand should make it very strong in place anyway.

So mix one part cement to four parts sand and no water. Then mix 50/50 sand and cement for the pointing, I presume I must add water to that though?

 

[Merlin5]

Well I got a gorilla tub, 40kg coarse sharp sand, 25kg cement, trowel and gloves for under £20 from builders depot. **** me though, I need to go weight training, those bags are heavy, particularly the sand!

So the problem now is, how do I move and store the sand bag once opened? It'll need to come through my flat to my garden shed but I can see it pouring out everywhere. Maybe I should put it in the shed before opening and then take what I need from there. Does cement ever go off if kept dry?

Ok sorted, moved to shed. I've kept the sandbag off the floor in case insects want to bite through it.

 

[Merlin5]

All done and yes, no water added. Took a few relifts of the slab to remove excess sand and cement and smooth it down before the slab was sitting flush. Then I used the excess to fill the pointing gaps. Hopefully it shouldn't wobble anymore. I'll mix some sand and cement with water tomorrow to fill in the hole in the wall.

 

[Merlin5]

Cheers sadat. I just bought a couple more tools. Needed a chisel for breaking grouting as I'm thinking of redoing the pointing on a wall. This chisel is really nice and weighty, only £2.85. And I bought a plastering trowel but for the purpose of using it as a float.

 

[Merlin5]

I filled two holes and it's gone off and feels pretty solid. Very dark colour though. I used an odd ratio, 5:2. Should I have used a different ratio to make it lighter coloured? Whoever repaired the section above mine got a grey colour and smoother finish. I'm quite happy to smash it out and start again. I think I should have added more water, it was a bit dry and clumpy.

 

[Merlin5]

At 2.85 that's is really good value. I'm not sure about the mixture but you can always sand it down to get as smooth as you want to depending on how high grit you want to go up to.

Yes, that chisel seems to be very good value. I wish I didn't have a massive bag of coarse sharp sand and had bought soft builders sand instead. Apparently coarse will always have a gritty finish and builders sand would be smoother and lighter coloured, better for pointing I think.

 

[Merlin5]

Yeah wrong sand, building sand is the one for pointing. However matching mortar colours exactly isn't easy anyway.

I'd buy a bag of building sand from builders depot as it will no doubt be good quality but they don't do smaller than 40kg and I'm running out of shed space. Wickes and B&Q do smaller bags of builders sand from a company called Tarmac, but according to reviews on the B&Q page, it's not good, full of stones and grit apparently.

 

[Merlin5]

I use tarmac sand all the time and never had an issue, however you can buy mortar prmixed in tubs as well for small jobs. It is a little more pricey but no bags of sand laying around.

Ah that's good to know Tarmac is ok. What is the amount in those bags, is it about 20kg?
The premixed mortar is a good suggestion too.

could you not sand down when dried? You still retain the problem of the colour tho.

Actually I sanded it with 80 grit today. Looking a lot lighter coloured now.