Slate cleaning questions

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Old 09-04-15, 06:04 PM
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Slate cleaning questions

see pic below
L side of slate has been cleaned with a Nyalox abrasive impregnated nylon brush and water
R side is original, stuff does not come off with muriatic acid
there is also a glob of ?thin set ?mortar

am a newbie
what is this stuff?
how to remove it?

history is complex
slates are ?3 decades old so lots of time for crud to develop
recently some loose slates have been cleaned and put down with new thin set and grout so ?grout ?mortar haze

thank you

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Old 09-04-15, 06:48 PM
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Try taking another picture from an angle. These pics don't show much. Also include pic of existing or other slates that these came from.
 
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Old 09-04-15, 07:42 PM
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Ok will get more pics when sun is out and slates dry (raining dark now)
Slate is "Vermont variegated purple" so each slate is different color
 
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Old 09-04-15, 08:37 PM
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Slate cleaning questions

Actually I have another pic
shows two slates cleaned with the Nyalox brush and the surrounding slates
again haze comes off with the brush if you rinse immediately
haze does not come off with muriatic acid with or without rinse

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Old 09-05-15, 03:16 AM
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I have no idea what it could be. I was hoping one of our experts might chime in when more pics were posted. My only though is perhaps its something like Thompson's sealer that could've been put on in too thick an application.
 
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Old 09-05-15, 04:21 AM
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Fresh TWS that is applied too heavy can have the excess removed with mineral spirits and elbow grease but TWS generally has a short life when exposed to sun and rain and should completely wear away in a few years. Muratic acid usually has no effective on paint type coatings so I assume it's some type of sealer.

How does water bead on the hazing sections compared to the clean ones?
 
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Old 09-05-15, 06:48 AM
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Thank you
Water does not bead. Rather forms pools that coalesce into even layer.

How about these explanations?
1) Many slates were loose so we had them picked up, cleaned and put back down with thin set and grout. Could it be thin set and grout poorly removed from the surface?
2) I guess slate chalks or effloresces. Could it be efflorescence?

In either case, how best to remove it?

Thank you again.
 
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Old 09-05-15, 09:13 AM
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Does the water behave any different on the areas that were cleaned versus the rest?

As far as I know. muratic acid would remove any cement based haze. Since it's usually best to start with the least caustic solution, I'd try a heavy duty detergent like TSP first.
 
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Old 09-05-15, 10:50 AM
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Water behavior same on clean and unclean. No beading, just pooling.

The brush takes it off without muriatic acid IF followed by a rinse.
Muriatic acid and rag does not take it off.

I read this about TSP <http://www.naturalhandyman.com/iip/infxtra/inftsp.html>
Sounds bad around a swimming pool. But could I suppose do major area with TSP and coping with just the brush.

Nevertheless will get some and try a small spot.

Thank you for advice.
 
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