Page 1 of 1
Posted: Mon Jun 19, 2006 11:59 am
by MikeA
Hi,
2 weeks ago I finished laying a 4m x 4m Stonemarket Yorkshire Riven patio. At the time, I noticed some of the slabs had slight dark marks on them from where they had been touching the slab next to them in the pallet. These marks got a lot more noticeable when wet, becoming a lot darker in colour. I positioned these slabs so as to not be too noticeable. Now, more of the slabs, especially the 300x300 ones, have started to get dark marks (usually irregular circles about 2inches in diameter). I've tried to clean with a wire brush but the area around the marks is now also slightly darker than the York Buff colour of the rest of the slab.
Is there a way to clean the marks off the slabs? Will they disappear in time? Why would a brass plated wire brush cause the mark to get worse?
Thanks.
Posted: Mon Jun 19, 2006 9:18 pm
by Tony McC
A wire brush of any description will only make matters worse.
Have yu been in touch with Stonemarket? Have you any photies?
Posted: Tue Jun 20, 2006 8:04 am
by MikeA
Not been in touch with Stonemarket yet. The marks are very similar to the ones I've seen talked about on other threads in the Archives (Dark Staining on Edge of Slabs) but are small and in randon places on the slabs. The slabs were laid onto about 6inches of hardcore base on a bed on 4 parts sharp sand to 4 parts building sand to 1 part cement (I have half a tonne of building sand I am trying to use up!) then dry jointed. The ground was fairly wet at the time (3 weeks of continuous rain) and we've had very warm weather since, so I think the marks are just due to dampness coming up through the slabs. The 300x300 slabs were quite a lot thinner than the others so maybe this is why they are showing the marks sooner.
Had another look last night and some more marks have appeared on other slabs but others have faded. I'll try to take some photos later to send you.
I'm quite happy to leave it for a few months to see if they all disappear... plus keep off the wire brush for the time being!
Mike
Posted: Tue Jun 20, 2006 9:28 am
by mouldmaker
These marks are most likely, as you say, caused by excess moisture rising up through the slab, carrying minerals from within the slab up with it. This may form a hard dark crust on the surface.
From Stonemarket's perspective (and you should notify them asap rather than waiting a few months they will most likely tell you that (a) if you saw it before you laid it, you shouldn't have done, and (b) it's a naturally occurring phenomenon and therefore outside their warranty conditions. That doesn't mean you shouldn't at least try to pursue it with them.
The marks will probably (but not definitely) disappear in time, but that could be anything from a few months to a few years.
The wire brush should be thrown as far from the area as possible and never touched again - if you find yourself tempted, slam your fingers in a door repeatedly until the urge goes away! All you will do is f**k the surface up and make it more prone to dusting and frost damage, as well as making it just look like it's been wire-brushed.
A last ditch solution is a weak hydrochloric acid solution, but this should be done with extreme care, or you'll suffer the same problems as with the wire brush.
Thouroughly wet the slabs - this will stop the acid soaking down into the slab. Brush a weak acid solution onto the affected area, let it 'fizz' for a minute, then rinse it off with copioous amounts of water. Do this as many times as necessary rather than leaving the acid to do the job all in one go. That will cause irreparable damage.