New Patio

[oneilly]

Hi guys, I need a little advise please, I had a patio layed in November not a great time to have it done I know, but I just looked out at it and found the grout between the slaps is crumbling away.

What do you think is the problem, I'm going to call the company back but I just want to know what I'm talking about before I call them!

Thanks guys

 

[r896neo]

Nothing wrong with laying a patio in november.

The best case scenario is that the pointing was just badly done i.e dry brush in. Or the frost may have got to it? If it was frosty the night or night after it was done that may have damaged it.

Worst case scenario is that the pointing is cracking up because the slabs are moving. There is no fix for this apart from lifting and relaying.

What slabs are they? sandstone, pressed concrete? And how were they laid? i.e full bed of mortar/ spot bedded/ laid on screeded sand.

 

[oneilly]

Thanks for your reply, I'm not sure how they were layed but the company are well respected, I think the frost got into them before they set.

They are polished sand stone.

 

[r896neo]

Ok, so its obviously a good few quid spent on it then.

In that case i would want to check the bedding mortar has gone off properly too? Are any of the slabs rocking at all?

If the pointing has been turned to marzepan by the frost then the mortar the flags are layed on will have been vulnerable too, Albeit to a slightly lesser extent than the pointing mortar.

Its hard to give you any more information without seeing it in the flesh. For reference, the bedding mortar should be a full continuous layer and not just big dollops in each corner and one in the middle.

The bedding should be very hard. Mortar that is solid but soft and crumbles when poked is a classic sign of frost damage.

 

[oneilly]

Thanks again, the slabs all feel very firm without movement.

It looks like it's just the pointing, would all the pointing need to come out or can it be scraped down until it hits solid motar?

 

[trowlerman]

if the slabs aint rocking then it sounds like a repiont , probably caused by frost

 

[Newapprentice]

Were you around when they did the pointing?

Were they on their hands and knees pointing with sand and cement or did you notice if they used a resin?

 

[oneilly]

No I wasn't around, but down the side of the house which is protected by the weather the pointing is fine.

But I do believe they were on their hands and knees, as they are a decent company.

 

[r896neo]

Not being on hands and knees does not mean a bad job. There are many high end resin products which perform brilliantly but unfortunately some of the cheaper 1 part brush in ones are crap.

There is no real way to check the bedding without lifting a slab. If the pointing has been damaged by frost then its not unreasonable to ask them to lift a slab and check the bedding mortar.

If the bedding had been ruined by the frost then the only way to check this would be testing it for hardness. The fact that the slabs don;t rock does not guarantee that the bedding is ok because frost ruined mortar dries out fine but remains very soft.

If you don;t want to lift one then poke out some of the pointing and try jamming something like a screwdriver down into the bedding mortar.
It should not really go into it at all.

(bear in mind to get to the bedding mortar you need to be about 25-35mm below the top surface of the slab)

 

[oneilly]

Not being on hands and knees does not mean a bad job. There are many high end resin products which perform brilliantly but unfortunately some of the cheaper 1 part brush in ones are crap.

There is no real way to check the bedding without lifting a slab. If the pointing has been damaged by frost then its not unreasonable to ask them to lift a slab and check the bedding mortar.

If the bedding had been ruined by the frost then the only way to check this would be testing it for hardness. The fact that the slabs don;t rock does not guarantee that the bedding is ok because frost ruined mortar dries out fine but remains very soft.

If you don;t want to lift one then poke out some of the pointing and try jamming something like a screwdriver down into the bedding mortar.
It should not really go into it at all.

(bear in mind to get to the bedding mortar you need to be about 25-35mm below the top surface of the slab)

Thanks very much for this, I'll have a little dig around tomorrow, just so I know, when they come back to replace the motar grouting, will they have to scrape it all out or can they just go over the top of the failed stuff.

That may sound like an ignorant question but I just want to know what I should expect when they come back.

 

[r896neo]

all of it must be chased out to a depth of at least 20mm

 

[oneilly]

Just a little update, the guys came back and raked it all out and checked under the slabs.

They did a great job.

Thanks for all your help!