dark grout dried white?

[hooja]

Hi all,
just layed an uncalibrated slate floor, what alot of work but happy with the result.
Only problem is i used anthracite flexible grout and in most places it has dried chalky white.
Left adhesive around 48hrs to dry,
mixed up grout as per instructions
Im guessing it has over emulsified, i mixed it up fairly stiff so cant have been that, i assume too much water got onto grout lines when washing excess of slates, i used a sponge and wrung out as much as possible but still guess water sat on grout lines.
Any suggestions as to how to bring it back to anthracite?
I have tried using a coarse towel but it just spreads the chalkiness.
grout lines are 6mm ish wide, grout rake? but dont want to remove too much.
help
thanks

[Polishtradesman]

I happens when you put too much water. If you mix grout as per instructions it means that water have to be in grout lines. Now you may try something like this - http://www.mapei.com/public/COM/prod...20fesca_gb.pdf

[Del W]

If you grouted in a very low temperature,that would affect the finish.
How about lightly rubbing the joint with sand paper,being careful not to damage the slate.
Try cleaning again with new sponge & clean water.I've done floors with black/charcol grout and after awhile all the joints start going gray because of foot traffic/dirt/dust.

[hooja]

Im guessing that its down to water sitting on grout lines after initial cleaning. How do you clean the excess grout off rough slate without too much water sitting on the grout? I used a sponge with regularly cleaned water and squeezed as much water out as possible each time.
Obviously i cant wait until it dries to clean it off as i will end up with grout all over the slates. sounds like a bit of a catch 22.
i will try lightly sanding the grout but the tiles do need another wash before final sealing, will this not just send the groput white again?
any more tips?

[hooja]

would grout stain remover help? im planning on using it anyway to clean of the last residues of haze, before final sealing, but will it help take the efflorescence off the grout?

[Del W]

This is on sticky threads posted by Dave,hope this helps.
Efflorescence What causes a whitish residue on grout?

Generally there are a few possible causes for white residue on coloured grout. When there is a whitish mineral residue on the grout, commonly this is caused by efflorescence. Similar to the white powder left in a drinking glass when a glass of water is left to evaporate, efflorescence is caused by minerals that are soluble in water being dissolved and transported to the surface of the grout as the water evaporates.

Typically, the minerals originate in the cement slab below the tile or in the ground below the slab.
Except in the rarest of cases, efflorescence does not occur from the small amount of minerals in water used to wash a floor. Nor when tile is installed with thinset (tile adhesive), are there enough soluble salts in the thinset to cause efflorescence.
Occasionally, when tile is installed over a thick mortar bed, the mortar could provide a sufficient amount of soluble salts to cause efflorescence but only if moisture is regularly passing through the mortar bed.
The next question must be where is the water coming from? Similar to the glass of water analogy, it takes a lot of water to dissolve enough minerals to be noticeable. As previously stated, typical cleaning does not provide enough water to cause efflorescence. Even saturating the grout joints with water during periodic cleaning generally does not cause efflorescence.
In exterior installations over concrete, rain can cause efflorescence over time when other conditions are right - especially with poorly compacted or porous grout.
More commonly, there can be moisture in the ground below the slab that is always evaporating. Even when a vapour membrane is installed below the slab, penetrations in the membrane may allow sufficient moisture to cause efflorescence. This moisture, invisible to eye, is steadily traveling through the slab, the tile cement, and the grout. More efflorescence will be observed if the concrete and grout are more porous

How do you minimize efflorescence?
There are generally effective ways to minimize this problem before tiling and some less effective options after the tile is in place.
Before tiling, if regular vapour migration is detected, remedial steps should be considered before tiling. Alternatively, a vapour equalization membrane can be installed before the tile is installed. There are also companies that sell coatings claimed to reduce moisture migration - however, these may interfere with the ability of the tile cement to bond to the substrate and should only be used if both the manufacturer of the tile cement and the manufacturer of the coating will warranty the installation system.
After tiling, sealing the grout with a penetrating vapour permeable sealer may help retard the rate of evaporation. Note, some caution must be observed in selecting the sealer - topical sealer's (acrylic sealer's) which coat the grout joint and are not vapour permeable may turn white from reactions between the acrylic and moisture - this is not efflorescence. Rather this is similar to the whitish haze seen with floor wax when it is applied to a damp surface.

[Dave]

It isn't Efflorescence, it is polymer leaching as mentioned above from wetting the grout joints , this can be avoided by frequent changes to washing off water.. and light smooth strokes to the grout lines just before the grout sets..

You can try grout haze remover and a white scotch pad to remove the polymer residue.