Pointing curing problem? - Is this normal?

[dibman]

I had 2 new sandstone patios and paths laid a couple of weeks ago and I think there is an issue with the pointing. It has set hard (rock solid!), but it seems to take ages to dry out after rain (I would say that around half of it is still 'dark' 2 days after the last bit of rain fell on it - so looks like only half of it has dried out, and the rest is still holding water (at least that's why I'm assuming it's still dark). There doesn't seem to be any obvious pattern to where it stays dark and where it dries out (i.e. it's not as though one large section is dry and the rest is wet).

I used a contractor that I know quite well and also kept an eye on the process. Details about the laying:

- Laid onto existing concrete base, with a suitable fall already built in.
- Laid onto a full mortar bed (sharp sand + cement, not sure of mix)
- Each area pointed the day after laying, with a 3:1 builders sand + cement mix. This was mixed almost dry (kind of crumbly). They spent ages packing it right into the joints and finishing it off - definitely not a rushed job!
- not sealed, although an adhesive was used on the under-side of the slabs during laying.

It's worth noting that this was installed 2-3 weeks ago, so it was really hot and sunny. After pointing the first patio, they realised that the pointing may have been drying out too fast, so for the second patio they fully wetted the slabs before pointing (leaving them to dry on the surface before actually doing the pointing!). They then gave the patio a very light sprinkle of water after the pointing has been finished. I don't think that this is a reason for the issue I'm seeing though, because I'm getting the same issue on both patios.

I don't think that variations between the mixes are to blame - they did quite large mixes, and I'm seeing this variation across areas where a single mix was used.

I also don't think that it's a case of not mixing properly - the used a cement mixer and had it running for a while. Also the mix looked pretty consistent, to me at least.

Finally, I don't think that the mix drying out during pointing is to blame, because again, I can see the same problem in areas where the start of the mix was used, and where the last bits were used.

I'm wondering if this is normal or not, and what I can do about it if it's a problem. I think that it's a problem, at least visually - I would expect a consistent colour in the pointing across the patio, and for it to dry out at a consistent rate. At least I would expect it to be dry after 2 days of no rain!

I'm really stumped here - any advice would be greatly appreciated!

I've attached some pics in the link below - these were taken over 1 week after pointing, and after 2 days of no rain.


images

[Tony McC]

That's most likely to be natural variation in the mortars used.

Having too dry a mix will result in a weak, friable and very porous mortar, which could explain some of it. Variations in the bed mortar, particularly the presence of voids where water can pool,could also be a contributory factor, and then there's the natural drainage of the site overall to consider: is there any risk of groundwater sitting for extended periods bnmeath the paving?

As an educated guess, I would think this variation will disappear over time as the mortars cure and they become clogged with detritus. I'd be sorely tempted to leave it for 3 months at the very least and then review it. Nothing I can see in those photies makes me worry that it should be taken up, re-pointed, or in any way interfered with.....for now.

[dibman]

Thanks for the feedback Tony - much appreciated!

Is this much variation in the mortars normal? I (naively) assumed that a color on mortar pointing would be pretty consistent. I had another chat with the contractors and they insist that the mixes were measured and mixed very carefully to be the same (although they also agree that there is variation just by looking at it!).

I'm not sure if water would sit beneath the paving for extended periods. The slabs are laid on concrete, which never had water pooling on it. I guess there will be some voids underneath the paving where water could get trapped though, if it can easily permeate the pointing (which it looks like it can in places).

I'll give it a few months and see how it 'ages'.

Thanks again

[Tony McC]

The usual contractor spec for accurate measurement of mortar or concrete mixes to "to the nearest bucketful'!

They only need half-a-spadeful less in a mix to give it a different appearance.

I had alad working for me years ago and his primary job was mortar and concrete mixing. In 5 years or more, I don't think he ever produced two mixes the same!