Patio pointing keeps breaking up - Advice needed please

[suggett1976]

I have a problem with a patio pointing job we took on a few years back.

First some history.

It’s a big (expensive) house in Handscross, west sussex.
The house and patio is around 15 years old.
The entire sides and rear of the property is made up of 600x600 riven edge slabs. The slabs are laid dry onto a ballast/sand base with large pointing gaps. The pointing is birds mouth.
A lot off the pointing had crumbled, cracked or missing completely, you could see colour differences where it had been re-pointed.

As a company we had quoted to re-point the entire patio.
All the old was raked out and a new sand and cement was put back down with a birds mouth point.
mixed with a cement mixer. Everything was gauged to keep colour consistency.

The job was carried out towards the end of the summer, not to hot and dry conditions.
After the first winter, and a lot of snow, most of the pointing crumbled and broke out.
As we were carrying out the job in two stages we were only 60% through the job.
As good will we raked it all out and started the whole process again. This time finishing both stages of the job to completion (at our cost)
Same weather conditions as before.

We warned the customer that we feel the reason for the pointing to crack is because the slabs are laid dry onto a sand base, the base gets wet, the frost comes and expands under the slabs, cracking the pointing.

We have just had another few weeks of harsh weather and snow, and the pointing has cracked AGAIN.
As you can imagine the customer isn’t too pleased and has at the moment casually mentioned it to us in passing, but I expect he will want answers.

A new patio that was laid end of last year, on a concrete base lasted fine in the winter.

So what are your thoughts?

Why does it keep cracking?

Is it the base?

Or are we doing something wrong?

 

[noseall]

When we lay slabs we lay them like a brickie would lay bricks.

We solid bed the slabs with sharp sand mortar and then tease a joint up the side of the laid slab, using the bedding, ready to accept the neat fella.

What this means is that the bedding mortar and the joints are all connected.

As one.

Solid.

We don't use dry muck either. Not too wet but enough water to keep everything 'knitted'.

Sharp sand mortar dries like bell metal.

These idiots that lay slabs on dry screeds or spots then brush in some lousy dry dust and expect it to last want shooting.

Blame amateurish T.V. shows if you like.

I don't know why you are having problems but it could be down to the fact that extreme freezing temp's are having an expanding effect on the so-called slab base and it is pushing out your pointing. Either that or water is finding its way past your re-pointing efforts and pushing it out this way.

If it is any consolation, re-pointing will not fix a lousy bodge laid patio. Ye canny polish a turd.

 

[suggett1976]

I agree with everything you said.

Where to go from here?

Im pretty certain the customer wont want to rip it up and start again.

 

[^woody^]

The problem is that the slabs are laid on a sand base and they are flexing. This slightly cracks the joints and further slight movement expands the cracks. Water gets in, freezes, expands and cracks the joints further

Most likely you will need to use a geofix product with brushes in and then hardens to stay flexible

A lime based mix instead of cement may also work, but it will be trial and error

 

[noseall]

Say to the customer that theirs is not the first patio that you have re-pointed but it is the first to encounter problems in freezing weather.

Mebbe drop a hint that you could get an impartial structural surveyor involved to verify that the problem lies with the inferior laying of the patio, not your re-pointing and that you would be happy to do so.

You have tried your best but you can not make a silk purse out of a sows' ear.

 

[r896neo]

First tell us what your doing, what sand, what consistancy?

I agree with woody, it sounds like the sub-base is not up to it and repointing flags that are moving will only end in failure.

I personally prefer plastering sand when pointing as its more workable than pure sharp sand but dries a lot harder than building sand.

As woody says the water permeable products may be worth a try but on a large area will be costly and should something go wrong you will be out materials plus labour. I have used rompox easy on quite a few jobs and it seems to last well and the colours are good.

 

[noseall]

The problem is we are talking about a patio. These are subject to a lot harsher conditions than any vertical surface.

The very fact that this thing needs re-pointing is a worry.

I would not suggest re-pointing using sharp sand, however using a rinsed sand such as plastering sand sounds sensible. Even plastering sand will be a slippery bu33er to trowel in.

 

[catlad]

Do you know what was used as weed barrier as that may be holding water.

 

[cotswoldbuilders]

Weve always laid ours on solid full bed of sand/cement and pointed as we go, never had no problems.
Always put down some well compacted hardcore as sub-base.

 

[WabbitPoo]

Your problem is that you didnt tell them at the outset that the pointing had failed due to laying technique. Now they'll be wondering why........

There's no point in repointing AGAIN.