The Brew Cabin

Hi Tony
I recently completed laying my patio and due to various reasons had quite a bit of catch-up pointing to do. I had been using Blue Circle's Snowcrete with a hint of buff cement dye and a fairly orange-ish sand. This produced a good mortar colour that really complemented the slabs (i.e. a very, very pale yellow-orange). Unfortunately and out of the blue, just after I'd finished the pointing, the heavens opened up and the patio got a good soaking. When the rain stopped and the patio dried, I have frustratingly found that the mortar is not now the colour intended. It is now many shades of boring grey, ranging from very dark grey through to an almost whitish grey, but certainly not the very light buff intended. The final colour seems to reflect how long the mortar was laid before the rain came. Luckily, the slabs don't seem to be affected (i.e. no cement or dye has washed out onto them) and the mortar appears very strong.
So, now the questions - Is there any way of colouring the already laid mortar to make it the very pale buff colour intended? Chiselling out the mortar and re-doing it isn't really an option as the patio is nearly 15m2 in total. I had considered mixing some dye in some water and kind of painting it on the existing mortar and hoping it would slowly soak into the mortar, dyeing it as it did so. Not sure if this would actually work and in any case, because the mortar now ranges from dark to light grey, might I just end up with mortar that is dark to pale buff? The slabs are Bradstone's Gironde and are a whitish-yellowish colour. Grey mortar looks truly awful with them.

PS I had never tried a project like laying a patio before, and did so using only the advice given on this site. The result is truly professional-looking (apart from a bit of bad luck with the pointing) and is testament to the quality of this site. Thanks for all your time and effort.

Is there any way of colouring the already laid mortar ?

No. 'Fraid not. :(

You could top it up, possibly, with a fresh, coloured mortar, or use an epoxy-based colouring, but neither are guaranteed to be successful. Mixing the cement dye with water will not work - the dyes work by reacting with and colouring unhydrated cement. They do not work with hydrated (cured) cement or cementitious products.

Have you got a photo of how the pointing looks at the moment? I might have an idea how you can get the desired effect, but it depends on joint width and pointing depth.

Tony
Thanks for the prompt reply. The patio was laid using 6 different sizes of slab, so it was necessary to vary joint widths as I went along to get everything to fit (as a bonus I also found that this further randomises the random effect of the paving). Hence, the mortared joints vary from as little as 4 or 5mm up to around 15mm. Joint depth is 40mm. I don't think there's really the room to top it up with fresh mortar, certainly nothing more than about a 1mm "skim" on top - would that be enough?

I'll try ang get some pics of the way things look at the moment, but I'll have to rely on the digital camera using the flash, as I'm at work during daylight at the moment.

Thanks once again.

With only 1mm available on top of the joint, I'm not sure it would work. I was thinking that, if you had 4-6mm or so, a coloured wet grout or a pumped mortar might have been viable, but you need a minimum 3mm of mortar to give it any real strength.

You do realise, don't you, that in 12 months time, the joints will all be a dirty 'detritus grey' anyway!

What about a masonry paint?

The good old British weather is always there to spoil things for us, eh?

I'd leave it a while and see how it weathers and ages before doing anything.