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Landscape Gardening
Damp patches on newly laid slabs - spot bedding?
Hello,
I am currently having a patio and path laid with Marshalls Firedstone slabs and some of the slabs are getting damp stains on corners and a dot in the middle. The landscaper has told me he has laid the slabs on what he refers to as a full concrete base. He told me this when he came to quote and it is written on both quotes. I think he puts a layer of mix around the outer edge and then 5 dots. Is this common practice? What is a full concrete base?
It has been down for 3 days which have been dry and quite warm. They are not all stuck down yet and are yet to be pointed.
Can anymore advise me on what has happened? Should I wait longer to see if they dry out? Should I hold off having the others put down in the same way? Would the damp marks go if the slabs were pointed? He has suggested a sealant, but would that fix it? I am unsure what to do, as the job is half done. How should I proceed? I've attached some pictures and would value any opinions? Is there anyone else I could ask?
What is the remedy?
Would Marshalls be worth a try, in case the slab is at fault? Don't know how to link my pictures to a webpage, they're on my laptop? please try this link
https://www.dropbox.com/sc/84kjqj8p9v99m75/AACxdjmUbklFMtOMhBCL7KKDa
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UPDATE
Thanks for the advice, it's much appreciated.
I cannot change the slabs unfortunately.
When I asked the contractor about his method and how it was different to the quote and he has admitted he has spot bedded, but claimed he has always used this method and never had a problem. Regardless I insisted on a full mortar bed, though he originally offered to screed, which I declined as I was unsure about the procedure. He has said he will lift, clean and relay them at his own expense. I feel I have got a favorable outcome, so hope he goes through with it.
1) As I know I live in an area with a high water table and my patio has issues with drainage due to the entire garden sloping towards the house - is there anything that I could have done to alleviate this?
2) What should the correct mix for mortar be? ie. content and ratio? Should he include sharp sand? (He previously only used builders sand.
3) His hardcore base consists of recycled hardcore/rubble (looks like all the bricks and rubble crushed into smallish pieces) and he has compacted it down with a whacker plate. As this is down and in his quote it cannot be changed, but can I pay for something to improve it and any drainage issues?
4) He has told me he points the slabs after they have dried out and are fixed. As the slabs are grey, what is the correct mix to ensure I get grey pointing and it remains grey.
3 Answers from MyBuilder Landscape Gardeners
Best Answer
Hi,
It looks as though your landscaper has done a very neat job indeed.
The trouble with these kind of slabs is that they are very porous. The dob and dab method is just fine as I lay slabs in this manor too as most of us would. It may be down to a high salt content within the cement and it is coming through, because these are not natural stone and pre-cast from cement it looks as though they have reacted.
密封不会帮助它只会在sta密封in, do not scrub or apply detergent as this may remove the dye or colour from the slabs. It's a shame as the cost of these per sqm you could have used natural sandstone and this would not have happened. Its not a fault of the tradesman just perhaps the quality of the paving as I have seen this happen from time to time.
One client I had this happen to did take it further with the manufacturer and was partially refunded but it was a battle. Its just an unfortunate situation as the cement can react with pre-cast slabs.
I hope it fades for you which is still possible, but if you do take it further and get a result do go for natural stone, you can bleach, scrub and clean it with no harm. Try infinitepaving.com they are my main supplier of natural stone and fantastic prices..
所以他利用核心和压实,这fine anything from crushed brick or concrete can be used. It should 4:1 ratio of sharp sand and cement, spot bedding is fine as long as you damp the underneath of the slab first and use plenty of mix to then tamper the slabs down into the mix with a rubber mallet, I have laid many patios this way and they have always been good and solid with no movement I only ever use sandstone so have never seen this damp stain come through on them. If the slabs are set tight and firm why does he need to re-lay them? Are they rocking about then!! As for pointing its a 3:1 ratio, but to be honest the best mortar is Easy joint sold in tubs for about £25 2 tubs would do about 20sqm, this stuff you just mix with water and brush in, comes in Grey, mushroom (beige) better than cement pointing as it does not crack in the weather or in the cold, we are all using it now to point and saves hours. Marshalls also do a weather point 365 check it out very good product. If he is re-laying the slabs he could lay a plastic membrane down first then bed onto this, this may stop the damp coming through, if its bedded on to a mix couple inches thick then this should not happen anyway. His method of laying the slabs is just fine, it could just be the minerals in the sand and cement reacting, his work does look very neat, but the choice of slabs are very porous ones and only made from cast cement themselves... One point on the pointing remember the colour can change due to weather conditions, if its very warm and sunny the pointing can dry too quick and cause issues like cracking, for a colour match he would need to mix a batch enough to do the whole area in one hit, sometimes the second batch is not always the same shade. seriously consider the the pointing compound I suggested its awesome stuff.
Paul
Answered 13th Aug 2014
He has spot bedded them if you can see it through the paving.
You cant see anything if they have been laid properly on a full bed of mortar.
He may referring to a concrete slab as a base for the paving and not the mortar. They should be laid on a full bed though so it needs sorting!!
Answered 12th Aug 2014
regarding the drainage, the dot system he`s used is best as the water will have somewhere to go ie through the slabs and soak away into the hardcore, if used with the easyjoint which is a lot more porous then cement the water would very quickly soak away
Answered 27th Feb 2016
