Issues with new flagstone patio - help! - Hollow stones, cracks, acid washing, etc

[JohnnyP]

I recently had a contractor install a flagstone patio for me in the Washington DC area. The material used was random design of Pennsylvania flagstone mortared (#2 portland cement, I believe) to a poured concrete foundation. There is a sitting wall enclosing the patio that is made of Hopers Creek thin stone. It was all new construction that occurred during February when Washington experienced colder than normal temperatures. It was a battle to get the contractor to wait for temperatures above freezing to do the work. We have had some problems that I believe may be linked to both the cold weather and some attempts to cut corners towards the end of the job. Being a non-expert I am questioning what I am now being told by the contractor. Here are the issues that are troubling me and the contractors stated response:

Issue 1: There is a hollow sound on many of the flagstone pieces ranging from very small (few square inches) to very large (a few square feet) on the flooring when you knock on them. Most of the hollow pieces have already experienced at least minor cracking in the surrounding joints. My concerns are that dropping something on a stone will crack it and water build-up under the stones causing additional joint cracking until they come loose. Contractor response: This is normal and no need to worry. The joint mortar is what holds the flagstone pieces together, not the mortar bond from under the stone.

Issue 2: The cracking of the joints. Again, patio was completed in February. We have experienced significant shifts in temperatures since the patio was installed. I understand that some cracking can eventually be expected, but would not have expected this much this early. I believe the hollow sound has had some affect on the cracking experienced to date. Contractor response: Normal from expansion/contraction. Is this really the case?

Issue 3: Varying colors in joint mortar. My wife had requested a grayish color mortar be used so that the joints were not as pronounced. We wanted the stone to be the main feature. No color was added to the Portland/sand mixture and we liked the original color. However, the contractor has had to come back several times already to fix missed items that were both expected and not expected. In doing so, various batches of mortar were used in various parts of the patio to re-point, fill-in gaps, etc. We now have a rainbow of colors in our joints that are very unpleasing to the eye. Contractor response: The patio needs to be “acid washed�. What are the affects of acid washing? Will we lose the gray color and be stuck with a more tan color in the joints?

Issue 4: Cleaning up of excess mortar on retaining wall joints. Not only does the contractor want to do acid washing to make the color of the joints uniform, he wants to acid wash the stone sitting walls to rid them of excess mortar. The excess mortar is mortar that is either (1) rough, (2) has bled onto the stone from when wet, or (3) a patch-work of mortar from attempting to correct outstanding issues. Is acid washing really the silver bullet that the contractor has stated? Can all these items be corrected simply by an acid washing? Are there any ill effects to the stone from acid washing?

Any help you can offer would be greatly appreciated. It appears that the weather has finally broken here and I would really like to be able to start enjoying my new patio! Thanks.

[lutonlagerlout]

hi johnny
the hollow sound normally means the flag is laminating or its not sitting on a full bed:which is wrong
acid wash???why didnt he just do a neater job in the first place? acid can discolor a lot of natural stone as its very corrosive,must be used with care
a picture would be handy johnny
cheers LLL

[Tony McC]

1 - The hollow sound could be delamination, but as this Pennsylvania flagstone is not summat we see over here, I'm not sure whether delamination is a problem with that particular type of rock. I'd be interested to know how the flags were laid, as hollow sound often indicates spot bedding, which is a crime against humanity

2 - Joint cracking: the rule is no mortar work unless the ambient temp is 3°C and rising, with no risk of frost within 24 hours. While some shrinkage cracking is normal, if there's so much you notice it, that suggests it's excessive.

3 - Mortar colour: It should all be one colour. Acid-washing is unlikely to rectify any shade difference.

4 - Acid-washing: often does more harm than good, and as LLL pointed out, it can discolour the stone. I'd be more concerned that a so-called tradesman made such a bloody mess in the first place!


Obviously, it all has to be tidied-up and made good, but you need to make it clear to the contractor that, should his suggested remedial work not turn out as predicted, he will be required to replace the lot: flagstone, mortar, and damaged walling!

[JohnnyP]

Thanks for the replies so far, very helpful. I will work on getting some pictures posted. The Pennsylvania flagstone will laminate some, but not to the degree that I am hearing the hollow sound in so many stones of varying size. The stones were not spot bedded when laid. They used mortar on the entire underneath of the stone. My fear is that the temperatures caused some issues. I had a capstone on one of the pillars and also a step down into my yard come lose. When the contractor pulled them up to reattach them, the mortar was sandy in composition in spots and obviously not adhesive to the stone. It also had a lot of "veins" running through it...as if there was an ant colony under it. Obviously, there was not total contact with the stone. I am worried that the other areas where I hear the hollow sound are similar. Off to get some pictures anyother advice/info is greatly appreciated!!

[JohnnyP]

Finally got the pictures to share. Couldn't figure out if I could add them to my posts, so I posted them on Yahoo.

Just click on this link (or cut and paste it)...

My]http://pg.photos.yahoo.com/ph....c=ph]My Patio Pics

Thanks for any and all feedback.

[lutonlagerlout]

overall it looks a very nice job,but i cant see that cracking getting better,surely once water gets in those cracks its game over??
what do you reckon lads?
regards LLL

[Tony McC]

A lot of the cracking looks like the archetypal shrinkage cracks, but the quality of the pointing is incredibly variable, ranging from excellent to appalling and all stages in between. I can also see what you mean about variation in mortar shade.

Personally, I'd be more worried about the workmanship than the colour: all cement-based mortars will weather and become much of a muchness over time, but the sloppy pointing will remain an eyesore for much longer.

[JohnnyP]

Thanks for your replies! The contractor came out yesterday and re-pointed the cracks in the floor and re-laid some of the hollow stones. He is going to let it set for 5 days or so and then do the acid washing. He is also recommending sealing the patio after 30 days or so. This is after last time he was out and said that sealing was no good and that he hasn't found a sealer he could trust not to discolor. I have read both positives and negatives on sealing. What are your thoughts on sealing a flagstone patio??

[Tony McC]

Leave it for at least 3 months and have them seal a test area or spare flagstone that's well out of sight.

Not sure what products are available over there, but, if it's owt like Britain and Ireland, there'll be one or two good 'uns and a whole shelf full of shite.

[Rich H]

The wall pointing is really awful. It looks like either the mix was too wet or it was raining at the time. I'm no geologist but if the sandstone has a high iron content the acid wash will cause big brown stains to appear which are irreversible.

[lutonlagerlout]

i know its rude to ask johnny but approx what did that project cost?
like the lads said the crazy paving looks fine, but it looks like it all went pear shaped on the wall a bit
i still think that overall it looks a fair job,come to luton you can see 10 times worse
cheers LLL

[seanandruby]

i would cut out the worst joints and re-point them myself. then a few strategically placed planters to distract your eye maybe.

[JohnnyP]

The total cost of the job was U.S. $11,300 which included the tear down and haul away of an old wooden deck and trellis. I've paid him about $8,500 to date and holding the rest until I am completely satisfied. The price was significantly lower than others. I know, you get what you pay for, but as stated some above, the overall job was pretty well done. It was towards the end and with the small touch ups where the main issues came from. The contractor was also eager to get the work during the slow time.

[lutonlagerlout]

that seems a fair price,crazy paving is one of the most expensive finishes,interesting you mention "slow time" we dont really have a slow time in the uk anymore,due to the lack of severe winters
cheers LLL