The Brew Cabin

Posted: **Tue Aug 24, 2010 11:08 am**

Hi Folks.

Last year or so I laid a large amount of Indian stonefor my patio. I machine compacted approx 2inches of MOT base, and then laid the slabs on a 50-70mm semi-wet/dry mortar bed. I then used Rompox easy to fill all gaps and everything was awesome and had no moving slabs.

Its a year later and some of the slabs sound like their moving. For example, you walk on one corner of a large slab, and you can hear the opposite corner creak - so they are def moving very slightly. I'm tapping quite a few of them, and areas underneath sound slightly hollow, even though I laid them all on a full mortar bed?

In addition, I have a 1mm gap around alot of the slabs where it appears the Rompox has shrunk?!?! I compacted it in when I laid it, and didn't scrimp ( I had loads left over) so not sure what is going on ?

Could it be that as I haven't sealed the stone, all the water is seeping underneath and causing problems?

Could it be that I did not make the mortar mix right, although I'm sure I took pretty good care in doing the mixes right, (5-1 if I recall what I did correctly)

Could it be that as I have some large Eycalptyus Trees nearby and my land is heavy clay, that they ground heave is causing problem to the subbase ?

Any ideas guys?

Posted: **Tue Aug 24, 2010 12:07 pm**

I used Rompox Easy recently and I have concerns about shrinkage. I also have 1mm gaps around some of my slabs.
I'm an amateur but I think in hindsight your sub base could've been a bit thicker (my sub base is a minimum of 75-100mm).
If this would've cause your finished level to be too high then you could've reduce the bedding layer slightly (mine is around 40mm thick)
Having said that if this is only a patio with light traffic then hopefully your layers haven't failed.

Forgetting about the rocking for a moment but the hollow sound is probably where the slabs are not adhered to the bedding layer.
I've read on here that it's not essential for the slabs to be stuck down so I'm guessing a slight hollow sound is acceptable? (as long as it doesn't sound like a drum)
Perhaps some horrendous freeze/thaw conditions followed by a scorching summer has caused the bond to break?

As for what has caused your previously stable patio to start rocking?
I dunno except for lifting a slab or two and inspect the layers

As for the Rompox shrinking, well I thought Rompox Easy was fool proof, yet we both have experienced something that 'appears' to be shrinkage.
Could be we've both done it wrong but I'm wondering if it's the new formula that they use.
Did you find the compound really moist and clumpy making it difficult to brush into the joints?
I found I had to use a squeegee and spent more time forcing it into the jobs and compacting it then expected.
I'm just wondering if the excess moisture in it can cause shrinkage when it evaporates?

I suspect I that a couple of my larger 900x600 slabs sound a little bit hollow but the rompox around them seems fine.
Does the hollow/rocking problems line up with the Rompox shrinkage problem. If not then perhaps there are two seperate problems?

Like I say I'm an amateur and will now stand back and be crucified by the pro's :laugh:

Posted: **Tue Aug 24, 2010 3:35 pm**

Also an amateur, the lifting of the slabs sounds similar to an issue I had (I had not jointed mine before winter set in).

Because the Rompox is porous, water will have drained through the joints into the bedding layer, the exceptional winter weather we had will have frozen and expanded this water and "popped" the slab off the layer.

I lifted my affected slabs and poured an SBR and cement slurry onto the bedding layer and dropped the slab back down, this essentially "re stuck" it to the bedding layer.

The only way round this problem again is to seal the patio which makes it non porous and should (in theory) prevent the slabs lifting in freeze conditions.

I didn't use Rompox when jointing so can't comment on this.

If I'm technically not correct, an expert will along soon.

Trevor

Posted: **Tue Aug 24, 2010 4:05 pm**

Did you mix any water with the sbr/cement.
Just figured that if used it neat a 5litre can wouldn't go that far. Or does it?

Posted: **Tue Aug 24, 2010 5:09 pm**

Just pour some SBR into a container you don't want to use again, and a rough ratio is 1:1 of SBR to cement, however you adjust the consistency by adding more or less cement. I got it to a just running consistency to pour. It does goes further than you think and don't be tempted to substitute normal PVA as it does not have the same properties as SBR.

I know it can be a bit expensive but you need to use the correct product to do the job right.

Posted: **Tue Aug 24, 2010 6:25 pm**

it could possible be the flags laminating
also it could be slight lack of adhesion to the bedding ,material
as long as there is no lateral movement it should be ok
LLL

The Brew Cabin

Flags sound like moving + rompox shrunk. - Year old slabs not fixed in place.