[klaaar]

We just finished a bluestone/mortar walkway. Before filling the joints, we mixed nine different small batches of mortar, each with a slightly different amount of dye. We compared the dry samples to existing mortars between other stone work on the property, and selected the best match. We used this mixture and mortared the joints several days ago. The mortar was mixed very thoroughly, pushed and smoothed into the joints, and smoothed with damp sponge. Now some of the mortar is bright white and some is a light gray as planned. We assume that wire brushing with water or a cleaner will remove the staining and restore a consistent color throughout. Any advice or experience you could share?

[Stonehenge]

If it's really light, it could be that those joints were made too smooth. The smoothness of the joint really has an effect on the color it takes when it's dry.

[steve lester]

why do you think it's efflorescence, if it is i have used a additive that you use in the mortor that get rid of it, i can't remember the name right now but i think its from baaf or something like that. i have it at work if you need it. and it does work i had a huge stoop we did with bluestone overlays with no mortar joint. the water entered to joint flowed to the tread and deposted huge amount of efflorescence, i tried acid, vinager, efflorescence cleaner everthing i could think of, all worked but it always came back. finally we have to take the whole stoop apart clean all bluestone and remix the mortar using this additive. this was i believe 1 or 2 years ago and i think everthing is fine the customer has never called back and said it came back and believe me they would have called back (big pain in the A__)!!!!!!!!!! i think the concrete for the stoop was fine, but we used bagged product for the mortar the first time i think that is wear we got the problem from the beginning, the second time we did it we used a different product for the mortar as well.

[klaaar]

Efflorescence was my guess because there are bright white areas and darker areas of the mortar. I'll try to post pics. Since there is some mortar residue on the stones, we plan to wash with broom/ brushes and a cleaner. We've used acid on other jobs. Perhaps if we use stiff bristles or even wire on the joints as we clean we could rough up the surface and give a consistent color.

Perhaps the mortar was smoothed too much as Stonehenge says, or possibly too soon.

[steve lester]

also if you get ride of efflorescence you can seal the job, efflorescence comes from water getting in the mortar and then drying on the surface, eliminate the water and then you eliminate the efflorescence.

[klaaar]

No matter what the cause, we need to find a solution. Available information on the matter cautions against acid washing new mortar, but since we need to clean the flags anyway, we'd like to scrub the joints as well to rough them up, in hopes in getting rid of any unwanted "whiteness". Does anyone have any suggestions? We have another 2 weeks of stump removal and planting work on the site, and we need to get the walkway looking good before winter sets in. One suggestion I heard was to apply a stain to the joints - would amount to a day's work, which wouldn't be a big problem.

Further research leads me to believe that the unwanted whiteness is laitance, which may be removed by etching techniques, since the unwanted material is hopefully not too deep.

[Stonehenge]

Klaaar - send me a pic at jeff[at]groundtradesxchangedotcom and I'll post it up.

I wasn't familiar with the term 'laitance' so I googled it - sounds like that's something that occurs with concrete, not mortar.

If we have a look, we may be able to offer more useful advice.

[klaaar]

I never heard of laitance before either, but if it can be a problem in concrete, I would think it can be a problem in mortar which is gravel-less concrete more or less, yes? Lime deposits might be a better term for what is fouling up the mortar surface. I guess efflorescence is used to describe another condition where a thin film tends to occur or recur, rather than a white discoloration showing immediatly upon curing, because of early tooling. Anyway, we will be cleaning the walkway tomorrow, and will slowly brush into the joints in hopes of stripping the fouled coating. Will try to take pics and send to you Stonehenge. Thanks.