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Posted: Wed Jan 31, 2007 8:18 pm
by bigwest
Would be very grateful on any thoughts on this:
I've been laying some white granite slabs which the manufacturer reccomends are laid using "white" cement to avoid any risk of staining. I have followed this precaution to be one the safe side but have noticed that the slabs seem pretty resilient to staining and are easy to clean.
Anyway, I now want to point them up using a black mortar dye. I've tested some, but after a day or so the pointing has gone from jet black to silvery grey.
Could this be due to the use of the white cement? Or maybe the joint was to dry when I tested it?
I will test some with normal cement but wondered if anyone had any ideas.
cheers
Posted: Thu Feb 01, 2007 12:42 am
by lutonlagerlout
in this scenario all i can advise is, be really. really. accurate gauging your sand cement and dye
remember to add the dye to the sand and cement and not to the water( my mate ben did this on a garden wall for the last 10 bricks and it stuck out like a tanner on a sweeps arse)
cheers LLL
Posted: Thu Feb 01, 2007 9:35 am
by TheVictorianCobbleCo
Even with grey cement your grout is going to fade with time, and you are going to have to be VERY careful grouting, the stains will become noticable weeks later. Dependent on the oxide you use, more money, better quality, you would need about 500gms to 1kg per wheelbarrow mix, or part thereof. Would it not be better to consider a specialist grout?
Posted: Thu Feb 01, 2007 10:04 am
by Tony McC
Black dye with white cement? Not an ideal combination!
You'd get better results using standard OPC, better yet with PFA (although that's not easy to source in small quantities) but for best results, you should ask your BM to get hold of a few bags of black-coloured lime mortar, which will stay black-ish for longer and give a degree of flexinbility to the pavement.
Posted: Thu Feb 01, 2007 6:18 pm
by Ted
I find the sun bleaches the colour out of black mortar/concrete pretty quickly if exposed. I rendered a wall in black render two years ago and now the wall is light grey! You need to seal the mortar/concrete to protect it from the sun if you want it to stay black...
e2a: i see no point in using white cement if you are using black dye; save your money and use OPC (the grey stuff)
Posted: Thu Feb 01, 2007 8:15 pm
by lutonlagerlout
i don't like using black dye because i have never seen it hold its colour over time,i wonder if there is a pozzolonic additive that would retain the black color?
interesting thoughts
LLL ???
Posted: Thu Feb 01, 2007 8:34 pm
by bigwest
It's a shame it has faded because the balck looks really good, as it does in the example pics on the main site. I followed the instructions from the site and when it went down it looked the nuts.
Where it has faded to grey it still looks OK but some has gone almost white - that's why I wondered about the snocrete maybe being the cause or the joints were too dry when pointed.
Thanks for all the comments, I think I will try another test with normal cement and see if using OPC does stain as the manufacturer off the slabs suggest it does.
cheers
Posted: Thu Feb 01, 2007 8:34 pm
by Ted
lutonlagerlout wrote:pozzolonic additive
You are just showing off now!
I think you need black aggregate (granite chippings?) and black sand (copper slag?). At least the sun can't bleach them, can it?
Otherwise a selaer is the only other viable protection, is it not?
Posted: Thu Feb 01, 2007 10:26 pm
by lutonlagerlout
You are just showing off now!
perhaps if i had got the spelling right ted, its pozzolanic,Doh!
its what the romans used before cement to make mortar go off,lots of things can do this including brick dust, soot, and silica
all of the pebble dash fell of my house (circa 1922) because they added soot/coal dust or summat to the lime mortar and it didn't work
tell you what though the mortar is still really black 
cheers LLL
Edited By lutonlagerlout on 1170368812
Posted: Tue Feb 06, 2007 1:21 pm
by mouldmaker
Using white cement defeats the object, just a bit!
There are lots of factors involved in using pigments, synthetic iron oxides don't fade but do 'weather' (no, not sure what the difference is, both end up lighter than you want!) over time. Use a dark opc (I think rugby is a little darker than most) and black sand (or failing that marine sand - some sands seem to leech colours which can lighten the effect) and 10% of pigment to weight of cement. That's the maximum it's worth using - it'll give maximum depth of colour, any more makes no difference and can weaken the mortar.
Edited By mouldmaker on 1170768131
Posted: Thu Feb 08, 2007 8:19 pm
by Rich H
For pointing, the dark grey polymeric sand maintains its colour (even though I don't like using it because it never sets as hard as is claimed). Perhaps if someone could find out what the colouring agent is that the manufacturers use, as it seems to be resistant to UV bleaching.
Posted: Fri Feb 09, 2007 12:03 am
by Tony McC
A polymeric that doesn't set hard? Does it begin with a "G" by any chance?? :;):
Posted: Fri Feb 09, 2007 7:55 am
by lutonlagerlout
second letter "e" perhaps????
waa,waa,waaahhh, waa, waa, waahhhh,
(my text redition of "the good,the bad, and the ugly")
lol
LLL