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Posted: Tue Sep 14, 2010 7:59 pm
by alan_james
I recently laid some natural black quarry stone slate slabs in my garden. I bedded most of the slabs on dry sand and cement base and bedded the edge slabs on a wet sand and cement bedding. On completion I brushed a sand and cement mix into the joints. I did not cover the slabs and it rained over night. Unfortunately there is some hardened excess mortar on a number of the slabs. It’s just a very thin layer but I am unable to remove this with normal brushing and soapy water. This was a 4:1 sand and Ordinary Portland cement mix that I used. How do I remove this mortar with out damaging the slabs or compromising the joints?
Sorry if this is covered already,but could not find it.
Posted: Tue Sep 14, 2010 8:07 pm
by Pablo
Are your flags Limestone or slate
Posted: Tue Sep 14, 2010 8:24 pm
by alan_james
Pablo, The slabs are slate.
Posted: Tue Sep 14, 2010 9:02 pm
by Pablo
Hydrocloric acid and a stiff brush. Wet the area down then apply the acid neat. Keep the acid in a bucket and dip a deck brush in it to do this. Once you've done an area 2mx2m rinse off with plenty of water and move on to next bit. The standard brick acid is just about ok but it's best to use the undilluted stuff. You need to wear thick marigolds and a respirator and cover all skin it's nasty stuff.
Posted: Tue Sep 14, 2010 9:35 pm
by alan_james
Hydrocloric acid..............hmmm. Pavingexpert says to avoid this as it could actually do more harm than good, this is covered in cleaning paving. as somone who has no idea im open to suggestions but dont want to ruin the paving either. 
Posted: Tue Sep 14, 2010 9:39 pm
by alan_james
and i see just under that warning there is this bit "Most granites, basalts, porphyry, slates and quartzite seem to be unaffected by acid or acid-based cleaners, but process with caution and test a small discreet area first" all i need now is a recommendation on where i can get this stuff. Band Q homebase have it?
Posted: Tue Sep 14, 2010 9:44 pm
by msh paving
You will have a hard job buying it from any standard shop,its a specialist supplier,give cookie a private message he will point you the right direction MSH 
Posted: Tue Sep 14, 2010 9:52 pm
by alan_james
thanks MSH, whoes cookie?
Posted: Tue Sep 14, 2010 9:57 pm
by Pablo
I get mine from the local concrete plant but I doubt they'd let a newbie near it. Try the brickacid first making sure the paving is just wetted down and not soaking or it will dilute to quickly.
Posted: Tue Sep 14, 2010 11:47 pm
by lutonlagerlout
i can get 32 % hydrochloric acid PM if you need some
LLL