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Stonemasonry

Kandlar grey sawn and polished sandstone

Anonymous user 23/02/2024 - 3.34 PM

Hi I have recently had a patio laid on a bed of morta but I'm concerned about blotchy damp spots appearing on some of the slabs, also a couple have a white residue coming up through them. The guys that did the work sealed the underneath as I was present whilst installation is this a common thing? Also they used a jet black azpect silicone grout, do I need a special cleaner to remove residue before sealing and how long would I have to wait before sealing.The Mr's is doing my nut in because I've had to remove plant pots and hanging baskets as a couple of petals had already stained a slab. Sorry for the long list. Thanks for the advice gents not too sure if I'm replying correctly I would gladly add pictures but for the life of me I can't see how any ideas would be appreciated

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6 Answers

Keystone Masonry

Rating: 4.9 out of 5

Glasgow

Hi yeh it's a list a picture would be a great help to really see. The damp patches should just be the moisture trying to get out. I would put a membrane down to stop weeds coming through. But I wouldn't have used silicone to grout it . Usually a fine sand and brush it in . The white patches sound like efloresance basically the salts in the moisture coming through. But I would really need to see it to be a 100% on any of that

Answered4 August 2020

Anonymous user

Did they seal the top of the slab? Also, did you say the staining had come up through the slab? Also, could you post a photo, please? If its salts coming up through then you could just use a stiff brush and some water. Whatever you do don't jet wash it as it will make it worse.

Answered4 August 2020

Kocka ltd

Rating: 5 out of 5

Palmers Green, London

Hi there, was very good that they seal the back of the stone, i hope the didn’t use any dark adhisive as the sandsyis very porous and can bring the darkness up face,to remove the darkness from the face i will recommend brick and patio cleaner, try in one corner first,if the stain doe go away, then we go for ano method, poltice, is a dust and we mix it with the bleach and apply in the datk area, cover with plastick membrane for 12 hours, and it sucks all the dirt up, dont seal it, remove the marks first otherwise the dirt will get trapped inside the stone. Recommendations: if you have leaves from the tree, try to not step on them, clean them away, they stain the stone very easy, Birds poop is the worst for the sandstone, Clean it and seal it every 3 months, Use water base stain stop from lithofin, All the best and good luck

Answered4 August 2020

Corner Stone

No reviews yet

Penzance

It sounds to me the there is lime coming through from the mort bed. I’m not sure why they used a silicone grout. But you will need to be careful cleaning sedimentary sandstone as it is delicate and will easily stain and chip if not done correctly. I personally would have laid a fine membrane between the mort bed and slabs.& pointed in with a lime based grout. Sandstone will absorb moisture from beneath as the base of the slabs won’t be polished. This may be the reason for the blotches coming through. I hope this helps. Best regards

Answered4 August 2020

Jmb construction

No reviews yet

Bradford On Avon

The patio needs to be taken up and a 150mm sub base of type one lime stone laid and compacted. The stone slabs need to be laid on a 50mm bed of grit sand. This will allow for seepage drainage as the slabs are porous. I have seen this problem many times. The edge can be retained with a cut stone beded in concrete. Sand stone is an acid stone and the pointing is best done with Holme sand a light pit sand can be blended with it to produce the correct colour. The reason I recommend Holme sand is because it is a washed sand containing no fines so it doesn't shrink and is a good base to blend a pit sand with . The pointing in my experience should be two Holme , two yellow pit sand and one ordinary Portland cement with the correct ratio of platicizer. It takes a while to mix properly so be careful adding the water.

Answered5 August 2020

Anonymous user

Firstly I would always prefer either photos or to visit the job. From what you are describing the white residue sounds like efflorescence which is caused from salt leaching out of product used or possibly from bad aggregate used. This occurs with wet aggregate and product. It can be cured firstly by brushing off and washing, if not successful products are available. The blotches on product could be caused from wet mortar being dropped on them. Personally I would not use a wet mix. I would lay them on a semi dry screed and paste the backs with a cement slurry. I would not use silicone to point them but use a semi dry mix with lime added.

Answered8 August 2020