New sandstone cement splashes and 'fossil' marks - How to remove them

FamilyM · Post: # 107905Post **FamilyM** Thu Feb 18, 2016 7:37 am

Hi, we have just had new sandstone paving slabs laid in the garden and when the pointing was done last week with a mix of cement in guns they have splashed the new slabs in multiple places. We complained and they are coming back next week to clean the slabs with an acid based product (Which after reading posts here I believe can damage the stone?) There are also a few large black 'fossil' marks in the slabs (shaped like ferns) which I wondered if can also be cleaned off and if these spread as we don't actually like the look of them. We haven't actually paid for the job yet so we are hoping this can all be easily remedied before we do! We obviously can't tell a 'paving expert' how to clean slabs so wondered what you thoughts were on what we should do? Does sandstone definitely get ruined with acid and if so would the slabs need to be replaced? If they use acid can it also damage our surrounding turf and Astro turf? Can fossil marks be removed? Thank you so much for any advice or similar experiences you can share.

RAPressureWashing · Thu Feb 18, 2016 9:01 am

Photos would help? Yes acid can damage the sandstone, they will most probably use Brick Acid, which is a NO NO, it can seriously damage the paving. Try to find out what they are going to use before they start. Re the fossil's they have been in the stone for 1000's of years, so you won't get rid of them, it is part of the appeal of sandstone.

Thu Feb 18, 2016 5:48 pm

the *fossils* are actually iron deposits and are naturally occurring in some sand stones especially mint
I thought brick acid worked if used in careful hands and the flags are pre wetted first,Roger?
we have used it successfully ,when things have gone wrong but must be tested on a small area first
ideally there would be no splashes in the first place ,but this is the real world
LLL

RAPressureWashing · Thu Feb 18, 2016 9:20 pm

lutonlagerlout wrote:the *fossils* are actually iron deposits and are naturally occurring in some sand stones especially mint
I thought brick acid worked if used in careful hands and the flags are pre wetted first,Roger?
we have used it successfully ,when things have gone wrong but must be tested on a small area first
ideally there would be no splashes in the first place ,but this is the real world
LLL

Tony, and that is the thing mate careful hands, My point is and I'm sure you'll agree people just go straight in with brick acid or hydrochloric acid without testing or looking at the strength of acid they are using, so best off saying on an open forum that best off not using, as if it goes wrong, "I read it on paving expert" that it was ok to use.
Seen to many f**k-ups with people throwing "acid" about.
If the OP can post some photos there is a milder acid to remove the "splashes" but would need to see the condition of the paving before suggesting what to use.

PS haven't forgotten about booking you in either

FamilyM · Post: # 107913Post **FamilyM** Thu Feb 18, 2016 9:27 pm

Thanks everyone for the quick replies! I mentioned my concerns to them today and they came and cleaned a test area. They watered down the brick acid so it was really weak and applied to a wet slab then used a brush and power washed down and it came up lovely. Back next week to complete the rest of the cleaning. We will learn to embrace and love the "fossils"! Thanks all

RAPressureWashing · Thu Feb 18, 2016 9:44 pm

FamilyM wrote:Thanks everyone for the quick replies! I mentioned my concerns to them today and they came and cleaned a test area. They watered down the brick acid so it was really weak and applied to a wet slab then used a brush and power washed down and it came up lovely. Back next week to complete the rest of the cleaning. We will learn to embrace and love the "fossils"! Thanks all

If they get the right results, then you can't ask for anymore then that. Pre-wetting the stone/slab is the major issue, so very glad they did that. Hope it all works out.