Granite patio & coping queries - Cleaning, sealing & jointing

[FBF]

I’m after some advice on granite please, which I haven’t been able to find from my browsing, so sorry if any of this has been covered before.

My project started in April and includes a raised koi pond with filter house, upper and lower patios laid with 20mm blue grey and silver grey granite, edged with 50mm Marshalls charcoal standard block paving, divided by planted walls topped with blue granite copings, and a new shed and log cabin.

The granite was laid 8 weeks ago on a full mortar bed (premixed and delivered to site and was kept watered as slabs were laid), over 150 – 200mm deep granite MOT compacted over Terram. The MOT is deep as we get a lot of ground movement round here. We were advised that it was not necessary to apply an SBR to the back of the slabs as they were being laid onto a full damp bed. The granite was not sealed in prior to laying as we simply couldn’t cope with the volume (approx. 132 SqM).

There are 5mm joints between the pavers which have yet to be filled with Rompox D1, which I have already purchased. My hope was to seal the granite with Lithofin MN Stain Stop prior to jointing as I quickly discovered how easily granite stains (leaves, bird droppings, coffee cup rings), and I know that the residue from the Rompox could take up to 6 months to weather away, and must be totally gone before sealing. I will seal the concrete block with, probably, Resiblock Ultra Matt (unless someone can suggest something better), at a later date as colour enhancement is the desired goal, once any efflorescence has had a chance to appear and been dealt with. Having conducted my own trials with Lithofin, in which oil sat on a slab for 7 days without penetrating, I’m convinced this is the product for me! I also need something fish friendly once cured for the copings round the pond.

I have put together a 7 page PDF of plans and photos that can be downloaded from this link https://we.tl/YZ22hTeDBa (5mb) which correspond to the following 6 queries:

1. All the walls have been JUB rendered with a Nanoxil top coat. The pond is fibre glassed, the internal walls of the planters painted with two coats of bitumen and the filter house with white masonry paint – all many weeks ago. This weekend, following heavy rain, I noticed water seeping through areas of the bitumen, and the top 3 – 4 rows of blocks in the filter house are saturated and the paint discolouring and peeling off. I now realise just how porous the granite is and that water must be seeping through the copings into the concrete blocks. No DPM or other waterproofing was installed beneath the copings. Will applying Lithofin Stain Stop be sufficient to water proof the copings to prevent this continuing or do we need to remove all the copings and install a DPM (I surely hope not!)? If sealing with Lithofin is sufficient, what will happen to any retained moisture in the blocks? Lithofin lets vapour through, but will this be enough for the walls to dry out as they can’t dry through the render or fibreglass or should I wait until there are no more signs of any damp in the walls? I’ve been told by Casdron the granite needs to have 4 days of total dryness before applying Stain Stop – but what will happen if there is retained moisture in the walls? Will that rise up or will gravity pull it down? I am so worried by the damage being caused to the walls from getting wet that I have now covered over the pond and the planters to keep any more rain from getting in, but in a manner to allow air to circulate to hopefully let it dry out.

2. There are some mortar stains on the granite and block paving from installation, but nothing too drastic. However, over the last few weeks I have noticed what looks like mortar coloured staining appearing on the silver grey granite that wasn’t there after the initial installation. Is this colour from the mortar working its way up through the stone? If so, will I be able to remove this with Lithofin Builders’ Clean? How long is this process likely to continue before nothing more will leach out as clearly I can’t apply Stain Stop on top of this? If I can clean this off, will Stain Stop prevent any more coming to the surface?

3. Some of the granite (both colours) have strange swirl like marks that are mostly visible when damp or drying out. I noticed these before the slabs were laid and wondered if they were pressure jet marks, but the merchant denied this and advised that they would disappear when down. They haven’t! Has anyone got any idea what these are and if they will ever go away?

4. Even on consecutive dry days, the silver grey granite can appear damp in places. It can sometimes look totally dry during the day but damp in the evening, I presume, from moisture in the air. Is this still just the mortar drying process? It doesn’t show up on the blue grey granite. I can’t figure out if this is because it is more porous than the grey (hence absorbs air moisture) or if it is more dense (hence it takes longer to dry out) – but it is most definitely very different to the grey. Either way – at what stage will this be safe to seal with Stain Stop because even with 4 consecutive dry days this ‘dampness’ can still be visible even after two months?

5. Which leads me to this conundrum – when to seal and joint? Clearly we need to get the copings sealed ASAP now, but should we be leaving the patio granite to next year? If so, and we press on with the jointing, will any residue from the Rompox cause any staining coming through to become permanent?

6. And finally… we have some slabs that have become loose and the installers have relayed them with silicone sealant. This has worked for all but one which has come loose again. Since then, some other slabs have become a bit ‘rocky’ and even more sound hollow if tapped, but are not actually moving. Is silicone OK to use to re-lay – if not how should this best be done? Does a hollow sound indicate that a slab will lift or is it safe to leave? My concern here is that I don’t want to joint if slabs are going to start lifting as it will be difficult and costly to have to re-joint again. The installers suggested that the only reason slabs are lifting is because it hasn’t been jointed. If so, should we just re-lay the loose slabs and push on with the D1 jointing?

Sorry for so many questions in one go. Any advice is very gratefully received.

[Tony McC]

All the questions relating to Lithofin products should be answered by their technical dept. hey are willing to sell theirproduct to you so it is the that should provide the technical support.

As for the loose flags "relayed with silicone sealant" - COWBOY ALERT! There is a FAQ explaining how loose flags should be fixed - it makes no mention at all of bodging them up with silicone sealant!

[FBF]

Hi Tony,

Many thanks for replying. I have had another long conversation with Casdron. My plan now – given the urgency to get the fish back in the pond, is to attempt MN Stain Stop on copings as soon as we feel walls have dried and keep everything crossed. If it goes wrong and reacts with any retained moisture in the blocks (the granite dries pretty quickly as it is so porous), then we will have to tackle that next year when we have another good run of dry weather, but we cannot wait around now to get the pond finished and the fish back in. Apparently MN Stain Stop can be removed with varying success (depending on how deep it has penetrated) using Lithofin Wax Off – which is good to know and hopefully helpful to others on this forum.

I've been told that whilst MN Stain Stop will reduce the ingress of water significantly, it is not an actual 'waterproofer' so there is no guarantee that rain will still not get into the walls once the copings are sealed. I have the builders round this evening and will see if we can get the copings off the filter house and planters to be able to put a membrane beneath without damaging the render. I will not risk removing the copings round the pond with the fibreglass. I would still be very interested to hear anyone’s thoughts on using DPMs in garden walls with copings. Were my guys wrong to have not included this initially or is this just my bad luck that the granite is so porous?

Acidic Builders Clean must not be used on block paving so I will have to try the Alkaline Power Clean to remove mortar staining from the borders, and if that doesn’t work on the staining on the granite, then very carefully spot clean the granite with Builders Clean (or Bero if that too fails), to avoid it getting onto the block paving. This is something worth knowing for anyone thinking of designing a patio with a brick edging like I did – you can’t necessarily use the same products on the whole lot!

I will have to leave sealing my patio till next year and reassess the need for sealing it then as I can’t risk a damp reaction to the Stain Stop on the greater area and I can't leave the patio un-jointed indefinitely. Next big task then is the rocking slabs and the jointing. I will discuss the correct way to relay the slabs with the builders later and show them your guide.

Do hollow sounding slabs always mean they will eventually move and will need to be re-seated or not?

[Tony McC]

Do hollow sounding slabs always mean they will eventually move and will need to be re-seated or not?

I've answered this at least half a dozen times over recent months: hollow sounds do NOT always mean hollow beds.

Flags laid on a full bed with even a minor void beneath can act like a drumskin and amplify the sound, making a hollow the size of a matchbox sound like a cavern.

This makes diagnosis of faulty bedding that much more awkward. We can't rely on hollow sounds when the flag is tapped to act as a reliable indicator of incorrect bedding. It *may* indicate incorrect bedding, but it's not infallible.

With experience, it becomes possible to sometimes discern between the hollow sound of minor voids and the hollow sound of spot bedding. The latter tends to give a deeper, more echoey, rounded sound, but it's not something I can describe in words. It's down to experience, which as we all know, cannot be bought.

[FBF]

Many thanks for your reply and my apologies that I had not seen it previously. My project involves two complete garden refurbs (mine and my mother's who lives next door - much to my other half's delight!), which I designed, but I have had to learn everything from scratch - not having ever done anything like this before. I very much appreciate the advice I have found on this forum and Paving Expert – and whilst I’ve clearly made some mistakes, I have avoided others thanks to this site.

There is a lot of conflicting information in the industry and online and it becomes difficult to know who to trust or believe in the end. Point in case - my water logged garden walls. Having not heard back from my builders all week, and reading ever increasing horror stories on line, I eventually spoke with local council Building Control who said DPMs should have been used and put me in touch with their damp proofing contractor. Hubby and I spent all week worrying how much it was going to cost to rectify or rebuild the walls - given they separate two patios and surround a raised koi pond with £1500 worth of glass, only to be told by the damp expert yesterday that we just need to have some weep holes and drain tubes put in, remove the masonry paint from the filter house to let the walls breath (apparently concrete blocks can take>6 months to dry out), and seal the copings with a water based sealant that will work with any retained moisture to create a water repellent barrier (though I'm still waiting for him to email me the details of this product).

Incidentally - the damp guy also said that re-seating loose slabs using waterproof sealant was an acceptable alternative to digging out and relaying a full bed - so again - what do I make of that?! You say 'cowboy alert' which is kinda what I felt - but council appointed expert contractor disagrees - which of course my builders were delighted to hear!!! I feel like hitting my head on a wall most days. This garden project has been more complicated, more costly and more stressful than the extension and total house refurb put together. I swear I hope I never have to move after all this!

So again - sorry that's you've had to repeat something you've written before, but I really do appreciate your help.

[Tony McC]

The council-approved Damp Proofing Contractor is now offering allegdly expert advice of paving installation? Do they do electrical wiring, attching cooling systems to Saturn V rockets, and glycolysis in e.coli bacteria, too? I ony ask because these subjets also have buggerall to do with a damp proofing contractor!

Using a sealant to fix loose flagstones is not, never was, and never will be, an acceptable method for remedial work. The damp contractor is a tool!

[FBF]

The damp contractor is a tool!

I only hope his opinion on how to fix the damp walls is right!!!

He finally sent me the link to the product he recommended I use to waterproof the copings - and it's Smartseal Natural Stone Sealer - which I know has had a few 'unfavourable' reviews on this forum in the past. Anyway - I spoke with Smartseal and this shouldn't be applied to a damp surface (hmmm); instead they recommended their Masonry Cream as an alternative (which should also go onto a dry surface), which lead me to research such products and brought me to Safeguard's StormDry Masonry Protection Cream http://www.stormdry.com/ – which is certified to provide 25 years of waterproof protection. Whilst there are a number of such creams on the market, and this is the most expensive (though still cheaper per litre coverage than Lithofin Stain Stop), it is the only one to carry BBA certification – and better still – can be applied to a slightly damp surface without risk of it going wrong or going white. Any retained moisture held in the concrete blocks below my copings will therefore evaporate through the breathable impregnator. Stormdry does not change the colour of the substrate and penetrates much deeper than other impregnators – up to 12mm depending upon permeability. It is suitable for natural stone – though not Limestone, and is water repellent within 2 to 4 hours after the one coat application, becoming increasingly waterproof over the next 2 months. All sounds rather promising doesn't it?!

Anyway – free Stormdry samples have just dropped onto my doormat so I’m off to give them a test on some granite cut offs. My main aim with the copings is waterproofing, but I’m going to see if Stormdry has any stain repelling properties also and what happens if there is moisture in the granite during application. If tests prove favourable, I'm wondering if this would be a suitable option for sealing the granite on my patio. Will report back with my findings - but in the meantime - does anyone have any experience of using Stormdry or another Masonry Cream on patios?

[Tony McC]

I've never used StormDry, so I'd be most interested to hear how you get on......

[FBF]

It’s been an interesting week! In preparation for my StormDry tests, I sat some granite in a tray of water to replicate what may be happening in my walls with the damp concrete blocks. This proved just how porous the granite was as it only took a few hours for the dry surface of the granite to go dark as the stone became wet from beneath.

So, for my tests I used dry, damp and wet granite off cuts. The water based StormDry had virtually no odour. It was very easy to apply as one coat with a paint brush. It went on as a white cream which turned transparent as it penetrated, which it did very deeply on my 20mm granite – almost all the way through in fact. Within the first hour of drying, I dropped some water onto the still wet surface to see what would happen. It went from clear to white again, which disappeared when I gently brushed it with a dry brush. Applying the product to dry, damp and wet surfaces resulted in them all looking the same – the only difference was that the damp and wet samples took a lot longer to look ‘dry’ - at which point they were just fractionally darker than an untreated surface. The product on the dry granite took only 4 hours before the stone returned to the dry colour, whilst the damp and wet took more like 8 to 10. However, I was disappointed that on applying drops of water to the dried stone after 12, 24, 36, 48 and 72 hours – whilst the water did bead, it also darkened the stone meaning that some water was penetrating the top layer. On speaking with Safeguard (who are extremely helpful BTW), I was told that the full waterproofing properties of StormDry could take up to 28 days to form
from the bottom up, possibly longer. Unfortunately, I really can’t wait that long to see if the product works for my purposes, given that I’d then have to wait another 28 days for it to cure if I then applied it – at which point I could be another 2 months down the road!

Now, the reason I was still hesitating to use the solvent based Lithofin Stain Stop was because I can’t guarantee my granite copings will be totally dry when it’s applied because of the damp walls beneath. However, I don’t think I’m going to have any choice. Whilst the water based version may be safer to use in this situation, I’ve had it confirmed from a very reliable source – that water based versions simply don’t do the same job as solvents. It’s chemically impossible!

This reliable source is Prof Denis Chamberlain – and a quick look at his LinkedIn profile will convince you that this chap really knows a thing or two about coatings! I came across this very helpful gent because I was looking for a solution to the peeling paint in my filter house, and he is the Tech Director at Northern Paints, the sole UK importer of Snowcem – a world leading, breathable masonry paint from (of all places!) India, which can be applied to wet walls. In my chats with him, he took interest in my project as a whole and explained to me that he had carried out extensive testing on granite at Brunel University for water and stain proofing and as such, it really has to be a solvent based silane/siloxane product if you want to achieve maximum waterproofing. He also explained that I needed to test my samples outside in rain as tap water molecules are larger than rain, and thus what may look water resistant in my kitchen, may not work so well outside. Fascinating!

Where it has been raining pretty solidly here for the last two days, I placed my StormDry samples outside, alongside the slab I had treated with Lithofin MN Stain Stop (Solvent version) a few months back. There really is no contest – the Lithofin treated granite hasn’t changed colour after all this rain meaning that water is not getting into it as blue grey granite goes instantly very dark when wet. The StormDry samples, whilst still beading, are as dark as all the untreated granite. I also tested cooking oil on my samples – Lithofin blocked it totally - for days, and left no trace when wiped off. StormDry didn’t and the oil soaked in and stained within an hour.

So there you have it! Decision finally made – Lithofin MN Stain Stop it is – regardless of the risk from my damp walls.

And the moral of this story – the one thing I wished I’d known before I started my project - if you want to protect your granite, you really should seal it on top before installing it! In my case, this would have been a huge undertaking given that I have some 130SqM of granite slabs, most at 90x60, but if I’d known then what I know now, I would have found some way to do this!!! Of course, you could always buy pre-sealed granite, but that would have been cost prohibitive for me.

I hope this experience helps anyone else thinking of using silver grey and blue grey granite in their garden. I’d also advise any one building garden walls to consider waterproofing agents added to the mortar as this would stop penetrating or rising damp becoming an issue. So simple in hindsight!

I’ll post back how I get on with the Stain Stop on my copings and if the damp causes any issues. I’ll also keep my StormDry samples going to see just how water / oil repellent they become after one or two months - just in case this is still an option for using on the patio. If anyone would like to see the photos of these experiments, let me know and I’ll upload them.

[Tony McC]

..... as tap water molecules are larger than rain....

I don't want to unfairly disparage the good Prof, but that's bollocks! Water molecules are water molecules are water molecules. It's two atoms of H with one atom of O, regardless of where it comes from.

The impurities/additives in tap water and rainwater might have some bearing on the way it reacts - rainwater is, naturally, slightly more acidic than fluoridised tap water - but that's not the same as claiming some water molecules are bigger than others.


Other than that, it's a fascinating insight and seems to bear up what many regular users find: that Lithofin SS+ is damned good stuff. The results of the Sealant Trial on sandstone also resulted in top marks for SS+....and far better than its water-based Eco sibling.

[lutonlagerlout]

just 1 point to add
all copings should have a dpm under them
nobody likes doing it,but it stops water getting through
granite although traditionally thought of as a hard stone is porous
let us know how you get on
LLL