problem with patio slab damp stains

[seneca]

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 a full concrete base, as per his quote. 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? Would Marshalls be worth a try, in case the slab is at fault?
Thanks[

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• seneca
• 8 Aug 2014
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• seneca
• 8 Aug 2014
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• seneca
• 8 Aug 2014
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• seneca
• 8 Aug 2014
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• seneca
• 8 Aug 2014
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• seneca
• 8 Aug 2014
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[wrathkeg]

Can't the contractor give possible plausible explanations? I'd want one of those before he attempted a remedy for fear that he'll make it worse.

The pattern of staining looks to me a lot like the sample on here of spot bedding (rather than full mortar bed) underneath porous slabs:

http://www.pavingexpert.com/layflag1.htm#spot

You might be able to get more info by looking at the edges of the slabs still at a free edge like the ones at the bottom of this picture:

//www.diynot.com/network/seneca/albums/21616/80802

Have a look along the free edge of the slabs, and maybe a careful poke about to see if there is mortar underneath the stains but not between them. It's hard to tell from the picture.

From that picture it looks to me like he is laying on mortar on top of rubble/hardcore, not concrete.

 

[seneca]

Hello,
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.
There are a few points I would like clarifying, before he relays:
1) Is there a good reference source I can follow to ensure it is being done correctly?
2) Anything specific I should look out for?
3) 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?
4) What should the correct mix for mortar be? ie. content and ratio? Should he include sharp sand? (He previously only used builders sand.
5) 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?
Here's a picture of it
.[/img]

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• seneca
• 11 Aug 2014
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• seneca
• 11 Aug 2014
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6) 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.
7) He never uses any additives in any of his mixes, should I suggest he does? (Don't mind paying for them if they will help.
Thanks in advance

 

[wrathkeg]

The answer to question 1 is www.pavingexpert.com . And it's there you'll find answers to questions 2 to 7

 

[seneca]

I've looked at the site a few times and it's a great resource, but vast and very detailed. Reason I listed the specific questions was to try clarify and summarize the basic issues which I thought I could bring up with the contractor, and be sure of the answers.
Thanks

 

[seneca]

Sorry to bother again, but need some advice-
My contractor has agreed to lift and relay them on a full bed, but insisted I give him details of the mix and it's content, as he will only do it once and exactly as I require. Therefore, could you please tell me the recommended ratio of sand to cement for the ideal mix and ratio for the full mortar bed and the kind of sand and cement that should be used. As the paving is a light grey colour should a different kind of sand and cement be used in order to prevent any future staining problems. ie. A white cement and silver sand? If so, could you please give examples/brand names. Is there also a specific mix (content and ratio) for the pointing that would not affect the light coloured paving.

Thanks.

 

[WabbitPoo]

Firstly, unlucky for getting a contractor you don't trust.

Secondly, a full mortar base on wacked hardcore is fine, but spot bedding is not.

Thirdly, 4-to-1 sand-cement is what I always use, with a mix of sharp and building sand.

No additives required.

A 5-1 mix of yellow sand and grey cement for the semi-dry mix, pressed in and ironed will give you grey pointing.

HTH