Wobble - Laying patio

[adamjth]

Hi,

Last weekend I finished laying my patio and had followed various online tips & tricks. This week I have reviewed the 45 large paving stones to find that 9 of them are slighly wobbly. I think I may have been 2 stingy with the cement as I started at 6 to 1 sharp sand to cement but then moved to 4:1 after I had my doubts (and for the area of the patio that has the most traffic) I did use a rubber mallet with a spirit level and so I am bit disappointed now.

Anyway what is the best way to put these stones down again as I now have the cement base to chip away at. the wobble on the stones was marginal so I wondering if I should have just put cement round the sides but I guess that is bit naff

cheers

Adam

[London Stone Paving]

Hi Adam

Unfortunately you need to relay them. It would be impossible to re-consolidate them properly by just putting cement around the edges. It would not last more than a few weeks.

Was the paving originally laid on a fulll bed of mortar?

[adamjth]

Hi,

Yes, I followed the usual instructions with 50mm MOT1 ontop of crushed hardcore. Then last saturday I laid a mortar bed at 50mm which I layed initially at 6:1 (sand to cement) but on the area near the backdoor I have gone 4:1)

I have pulled up the stones now so my question is how do I put them down again keep them level against the stones around them. I guess I got to scrap the new mortar out and then put some fresh 4:1 mortar down?

thanks

Adam

[London Stone Paving]

Just scrape all the mortar out and start again. Take care that when you are lifitng the old mortar that you dont dislodge any of the slabs around them. This can happpen because all the mortar you need to scrape out will be bonded to the mortar under the good slabs

[adamjth]

Thx do you think 4:1 is the best mix? I read some peeps say is:- 3 sharp: 2 soft: 1 cement

[London Stone Paving]

I used to use 4-5 parts sharp sand 1 part cement when I laid paving. Lots of people do use a combination of sharp sand and soft sand though. I think the combination of soft and sharp makes the mix more pliable, which may suit you more.

[local patios and driveway]

could have been a dry mix that didnt give good adhesion to the slab. i would run a grinder around the outer edge of any slab to be relayed, then hammer and bolster the concrte out and use a pretty dry 5-1 sharp mix (so dry that you can make a ball of it in your hands that will hold its shape but if you toss it in the air it falls apart.) then use a slurry (1/4 bucket of water and i shovel of cement dust, mixed up) to bond the slab, easy, no mess and you will get adhesion via the slurry and save the day. each slab should only take 10 mins start to finish

[London Stone Paving]

No doubt that applying a slurry would give extra adhesion but is it not over kill ? (unless the stone is slate, then a bond bridge is essential). Laid myself and seen thousands of m2 of paving laid and never seen the need for a bond bridge unless it is a slate or maybe a granite.

What is the paving material you are using Adam?

[local patios and driveway]

the nice thing about using a dry mix is that you can accurattly screed the small area, fit the slab and if the levels are right apply the slurry.

[seanandruby]

Hi Adam. I can't see why you would change your mix halfway through a job. I personally think your mix was too strong for a patio. If your flags have stuck to the bedding it will make it that much more difficult to lift them and clean them. Also it will be more difficult to take out the bedding without disturbing the neighbouring flags. Depending on the condition of your sub soil it is not necessary ( sometimes) to have a cement bound bedding material. Maybe 8/1 or even 10/1 would of been a better option, or even just sharp sand unbound.

[adamjth]

Hi, I am newbie and reviewing the online materials I have seen various ratios recc'd on DIYdoctor, DIYNOT and this site. When I initially started laying the slabs I started to have my doubts so I switched to a stronger mix. This is the type of stone I am laying its a 600cm x 45cm x 4cm and I *think* its a flagstone type:-



Forgive me for being being ignornant but if you laid them on sharp sand alone what would bond them?

[seanandruby]

I'll pretend i did'nt notice you mention those other sites. That is where you went wrong. This site is the only one where you will get the right answers and be shown by the brewers and on site index how to go about it. You will get some conflict of how to do it and what to use but most of the lads on here are highly experienced and have adapted their own methods over time. we can only suggest to you, at the end of the day it is up to you to choose. Tony mc ( the gaffer ) has gone through a lot of trouble to set up this site and index and is second to non in the world. Please read the index through again and again and ag......But please stay away from rogue sites that tell you the wrong way of doing things. Why would you want to bond the flags to the bedding, it is a patio with hardly any weight and no traffic ?

[local patios and driveway]

this is the only site where people really know what they are saying, like sean said. if its wrong here you are gonna get jumped on hence the accuracy of advise. take this site as gospel, i do

[Turbina Magnum]

if slabs are wobling slightly and its not sandstone, and taking in to account that there is good bit of them wobling - to save money and time, I would take up all of them, fit screeding bars and screed literarly 3mm of sand on top of area and relay slabs. That way low spots will be covered with thin layer of sand and slabs woun`t woble but good spots gone have only 1-2 mm sand.
Relay seperate slabs is nightmare; If you gone be takeing out seperate slabs, the question is - how you do it without dameging them? With extractor? And if you dont have "trained eye" you be strugling to fit those slabs back in spot as bedding will be low or high and then you have to get them out again.
If it is sandstone, then sure you can relay each seperately.

[London Stone Paving]

if slabs are wobling slightly and its not sandstone, and taking in to account that there is good bit of them wobling - to save money and time, I would take up all of them, fit screeding bars and screed literarly 3mm of sand on top of area and relay slabs. That way low spots will be covered with thin layer of sand and slabs woun`t woble but good spots gone have only 1-2 mm sand.
Relay seperate slabs is nightmare; If you gone be takeing out seperate slabs, the question is - how you do it without dameging them? With extractor? And if you dont have "trained eye" you be strugling to fit those slabs back in spot as bedding will be low or high and then you have to get them out again.
If it is sandstone, then sure you can relay each seperately.

I'm gonna have to disagree with a lot of what you have said there.

lifting up all the slabs and laying a screed over the top sounds like a recipe for a complete bodge. It would be much easier to just relay the loose ones


Taking individual slabs out does need to be done very carefully. i would agree with local patios and driveways and run a grinder around the outside of the slabs and then gently remove the mortar in small sections.

I always found it quite easy to relay odd slabs because in most cases you have a few fixed edges to set the slabs too.