Refixing loose patio slab

[Merlin5]

Hi guys. 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 or dip in the area under the slab. 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 or building sand or it doesn't matter, 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? And a gauging trowel? I also want to fill a small 3 inch by 1 inch hole in my front wall.next to the window frame.

How much sand and cement do you think I should buy? Will I need more than a 20kg bag of sand and a 25kg bag of cement?

Do I need a tuck pointer for the mortar joints around the slab and a piece of old hose to finish the mortar joints?

 

[ktuludays]

Lay the slab on a dry bed of sand/cement 3 parts sand to 1 cement.

1 bag of sand and cement will do both jobs, you'll have plenty of cement left.

Building sand will suffice

 

[Merlin5]

Lay the slab on a dry bed of sand/cement 3 parts sand to 1 cement.

1 bag of sand and cement will do both jobs, you'll have plenty of cement left.

Building sand will suffice

Thanks ktuludays, much appreciated.
Actually, I can't find a 20kg bag of sand, only this and I've no idea how many kg is in the bag. Think it'll be enough?
https://www.homebase.co.uk/sharp-sand_p921213

As I'll be mixing 3 parts sand to 1 part cement with water, what do you mean by 'drybed' of sand and cement?

 

[ktuludays]

Thanks ktuludays, much appreciated.
Actually, I can't find a 20kg bag of sand, only this and I've no idea how many kg is in the bag. Think it'll be enough?
https://www.homebase.co.uk/sharp-sand_p921213

As I'll be mixing 3 parts sand to 1 part cement with water, what do you mean by 'drybed' of sand and cement?

At that price it's probably around the 20kg mark.

Mix the sand and cement dry and fill the void under the slab, level off, lay your slab and water afterwards. This should be sufficient. If you want to mix wet you'll need to dig out the base that's currently there under that slab.

 

[Merlin5]

At that price it's probably around the 20kg mark.

Mix the sand and cement dry and fill the void under the slab, level off, lay your slab and water afterwards. This should be sufficient. If you want to mix wet you'll need to dig out the base that's currently there under that slab.

Thanks. How do I water after the slab is laid, and shall I make up a 3 to 1 for the pointing and add water to that I presume?

 

[Ian H]

I would splodge it down on a wet mix.

 

[Munroast]

If what is in there already is sand - then dig out 3 or 4 inches, mix a shovel full of cement into the sandy stuff that has come out - put it back in (without adding water), lay slab on top and tamp it down until it is in the correct position - repoint - job done. (the natural dampness in the ground will help the cement go off and semi bond it all together.)

You may very well get away without using cement, plenty slabs are laid very successfully onto sharp sand.

 

[Merlin5]

Thanks guys. I just bought 40kg bag of coarse sharp sand, that was their smallest bag, 25kg general purpose cement, gloves, gauging trowel and gorilla tub for under £20 from builders depot. I need to go weight training, these bags are ******* heavy! I've moved them to my shed before opening or there'd be a right mess moving from front patio, through my flat and into the garden. I'll just measure out what I need straight from the shed. What's the best way to protect the sand and cement from moisture once opened, put a thick plastic bag over the bags? And if kept dry does the cement last long?

 

[Merlin5]

All done. Took a few minutes of relifting the slab a few times to remove excess sand and cement and smooth it down because the slab was sitting a bit high, but now it's pretty flush with the rest. And then pointed the surrounding gaps with the leftover sand and cement. No water added to anything.