Downpour during patio laying

[Midge]

Slightly off topic since I didn't do this myself due to a bad back.....

Had my patio re-done a week or so back using Marshals stone-effect slabs. Nice weather so not my builders fault - but suffered a sudden and torrential downpour of rain within a short period of the slabs being pointed with cement.

In spite of my builder getting a tarpauline across them, the cement has dried with a white surface, and in places this has gone across onto the face of the slabs - in most cases no more than half an inch around the edges but worse in places, and it does look a little bit unsightly at the moment.

He is suggesting it will weather out but he will come back and sort it if not. Is that the case as I'm not sure what the white residue is?

I'm loathed to experiment with anything harsh to help the process as I assume the colour on these imitation stone products is a coating over a composite base and not sure how deep that colouring is.

Thoughts/ideas?

TIA Midge.

[Palindrome]

From the POV of the pointing, you really need to give it several weeks before doing anything. It may easily mostly fix itself. After that,a wash or a *gentle* application of a *stiff* brush when it is totally dry may be all that is needed to remove whatever is left.

Every week that you can bear to leave it looking like that is more time for the cement to do its job. Rush it, and you will damage the pointing, needing it to be redone as repairs are never as good as getting it right the first time.

IIUC, the white stuff is a very, very thin layer of silica crystals which reflect the light very well and hence look very white.

A stiff brush will remove them - but, doing so before the pointing has had time to cure, the force needed to do that is quite enough to remove pointing that you don't want damaged..

-- Sue

[Midge]

Thanks Sue - just tried brushing a corner of a slab and it does seem to be coming off with a bit of elbow grease. I'll leave it a bit longer and see how it goes.

Midge.

[EricP]

Go to your local diy shed and look for Brick Acid. This should remove it but be careful as it's a simple but nasty acid. So take obvious precautions in it's use.

[Midge]

Thanks - I was a bit wary of the acid approach, but as it happens, it does seem to be weathering away as has been suggested. Reckon another fortnight and a bit of help with a brush might jut do the trick!