Acid disaster

[mark61]

recently completed 50 square meter patio in black indian stone bought by customer which i took to be slate as it looked and behaved like it; i.e black,dense and could split along the grain. 4 sizes laid in repeatable random pattern. Usually follow tonys advice re jointing with semi dry mix but made mistake and mix ended up wetter than should be. carried on as had mixer full, time was tight and i thought i could clean with brick acid as i have done before with no problem. HOWEVER after it had dried there was heavy staining where spills had occurred, where i had initially brushed along the joints and darker and lighter lines where different acid washes had overlapped. The colour on the least affected flags had basically faded to grey. found label hidden on one crate which described the stone as black limestone. realised cause of problem. even though acid was heavily diluted and washed off quick the surface has reacted extremely. to further compound this cack handed disaster i spilt a splash of petrol while filling washer which was spread around while washing off leaving an area black. customer feels that problem will be solved by applying a sealant which he had intended to do anyway. while the problem was much less noticable when flags were wet i dont think this will work as splashes and lines will be preserved by sealant.my current plan is to treat individual flags with more acid to even out staining before applying colour enhancer and sealant after checking out effect of this on spare pieces but not confident of success and uncertain of how to treat petrol stain.HELP!!!!! does anyone know whether there is an abrasive solution to this? how deep might the staining have gone into the stone? it is obviously sensitive stuff and what would be the best enhancer and sealant to use on this. Hope you guys can help. been using this site for years, best website in world bar none. information so comprehensive that i've never needed to ask a question before. Thanks in advance. mark

[lutonlagerlout]

we all drop a bollock from time to time mark,its how you deal with it that matters
roger can advise you better than anyone on sealer's/washes etc.
R and A pressurewashing
personally i wouldn't add any more acid in the meantime,it could exacerbate things
I bet you wish you had skipped that barrow of muck now eh?
good luck LLL

[mark61]

thanks LLL,i do, although its more the acid i wish i hadnt used as i noticed that the pressure washer was happily erasing the mortar stains on its own without damaging the joints as i left it a couple of days before cleaning. re the best people to advise on different subjects do i wait until someone replies to this post or can i contact them in another way? cheers.mark

[selfbuider64]

Well more acid would makes things definately worse. As it's the black limestone you are getting a reaction between the alkali stone and acid. One thing to note is that when unsealed this stone ALWAYS fades to light grey. If you want to enhance the colour try lithofin stain stop plus.

If you want black stone outside you can use slate ( welsh and brazillian are colour fast Chinese spannish and Indian are not) black Indian sandstone but that's not really that black , basalt or sawn Chinese black sandstone. On the basalt you do need to be a bit careful as one of the Chinese ones reacts to acid.

In a nutshell if it limestone paving don't use the acid and always advise the client that black limestone will discolour with time.

[mark61]

thanks for reply selfbuilder. my dilemma is that the stone is all down and whereas i wont be using more acid on the flags that have faded uniformly the worst bits are where the acid has splashed or overlapped leading to differential staining. i have experimented on some spare stone and am able to even out the staining, therefore my plan is to do this on the worst affected flags one at a time before applying a colour enhancing sealant. i have bought some by LTP and will experiment further with this.

[mark61]

p.s i will take your advice and never use acid on anything else except terracotta and brick and welsh slate (which is what i thought it was,so other lesson learned,read the bloody label on the crate) ta

[mark61]

i tried two coats of the "colour enhancing sealer" on one piece and one coat of boiled linseed oil on another. the one with the linseed oil looked a lot better i.e darker. the sealer seemed more water repellant but didnt really darken it much and would have needed several more coats to get near the oil.
As that would cost well over £150 quid and the oil would be less than twenty i'm going for the oil after i even out the staining (which also worked on the sample).
Cant find much on the net about using linseed oil on stone. What i have found suggested using two coats diluted 50-50 with white spirit and that raw oil yellows less than boiled oil but ill use what i can get. Anyone had experience of doing this or any thoughts?
Am going to use soft floor brush to apply before wiping down with hessian as sample looked shinier in parts when dry. second coat the next day (hope it stays dry) probably a good idea to try this on a spare piece first come to think of it.
seems like a good "old school" solution and customer is happy with sample.
Having also read a bit on the website about this material and watched it bleach in the sun the last two weeks im sure it would have gone light grey sooner or later anyway "something they dont tell you at the stone merchants".

[cookiewales]

oil is a old method we use to clean slate after pointing with cement and clay fired tiles and engineering bricks as well and it works on kotah stone wd40 on a cloth 3inone oil also works well only small amounts needed all ways test before use :;): :;):

[selfbuider64]

Personally I would go with WD40 as propsed by Cookie. LTP do a linseed product may be worth looking it up :

http://www.ltp-online.co.uk/tile_sealing_products.html

I sell stone for a living and always advise clients that the black limestone from India turns grey. It's remarkable how many companies selling natural stone have very little knowledge on the product.

[London Stone Paving]

Afraid that I have got nothing new to add to this topic. Only to share a recent experience of ours with black limestone and acid based patio cleaner.

We are in the process of building our paving showroom. Limestone section consisted of Kota blue, kota black & kota brown. Paver did a great job of the laying and it looked fantastic. I then had to then leave the office for the day. When I got back in the morning all we had left was Kota white. Turned out that the paver had made a bit of a mess of the pointing and in his eternal wisdom decided to use Lithofin builders clean (fantastic product by the way most of the time) to try and make good. He had used it before on sandstone so he thought he was doing the right thing.

We ended up having to relay the whole thing. Message is dont use anything acid based on kota limestones. EVER.

[seanandruby]

.....and don't fill plant with fuel on new paving. As always prevention is better than cure :;):

[PBRADY]

I have just had black riven limestone laid and the landscaper used a mortar cleaner before sealing. It has left splash marks all over the patio (looks like someone has chucked several cups of tea over it) He told us to wait for the weather to calm it down, but 6 weeks on, still much the same. We are thinking of claiming against him.
However we used Colourplus Universeal on a couple of slabs which has darken the slabs (which is what we wanted) but we now keep getting the odd white mark coming through. Can we get rid of these now this has been sealed, and if so, how? I am also interested in the linseed oil. Would this come off on clothes if someone sat on the patio, and can you later use a sealant over it should we want to change?

[London Stone Paving]

Claiming has got to be a last resort. Explore every other avenue before you down that route.

I personally have no experience of linseed but there will be plenty of people on this site who do.

My advice would be to wait until you get some good info from the site and then sit down with the installer and try and sort it out together. Mistakes are made, but in my experience people are always willing to put things right given half the chance

[PBRADY]

I agree and I have asked him several times for solutions, and he suggested let the weather resolve it and the last resort was to claim of his insurance.
I got a text this afternoon from him in which he has just told me he has no insurance!!! Worryingly, he is currently working on a new patio for an elderly couple that don't live to far from me. If he apologised it would be a start.
We spent over £3000 and wanted it to look nice for our daughters 21st birthday in July, so we are keen to do anything to get it looking right and protected before food and drinks could be dropped on it.
Any suggestions would be greatly received

[selfbuider64]

This is an age old problem with this black limestone. Even if the contractor had not split something on the stones they would inevitably turn grey. This is due to a reaction within the stone to UV and possible lightly acidic rain. You can certainly seal it but you will have to repeat this over the years. This black limestone is great inside outside if you want grey it's fine if you want black then you need to specify something else.