Laying saxon mocha slabs - Hollow sound from a few of the slabs

[Hamachi]

i laid 50sqm of saxon mocha paving 8 months ago on full mortar beds sharp sand 5;1 but have noticed a slight hollow sound from a few even though there is no sign of movement in the slab itself.I also pointed the area with geofix all weather which has now turned a dark colour with algae on some parts. Repointing is now the only option as my client is dissatisfied with the outcome.Can u recommend a more suitable jointing compound .

[lutonlagerlout]

hamachi if you read through these forums geo-%$£" does not get glowing reviews
sand and cement is best IMHO
i get on fine with easipoint but you need dry weather

2 part resins are great but bleeding expensive

gftk 850 and romex D1 being the best

LLL

ps had to repoint 6 patios myself where we used the Geo stuff

[Hamachi]

Great stuff will give that a try thanks very much for your advice

[r896neo]

the other option is flowpoint (or larsen fjm which i use but may not be available where you are) which has the benefit of being fast to apply like a resin but is more difficult to clean up. therefore it doesn't suit all jobs if you have no where to collect the run off. Also its less than half the price of a resin.

You have the confidence that it is a cement based product so will last better than the wonder products that didn't turn out to be so wonderful.

I like LLL have had to repoint 3 patios that were done with rompox easy 2 years ago.

[Tony McC]

Hollow-sounding flags happen for all sorts of reasons. <spit>Spot bedding is the most common reason, but even a full bed with a rippled surface can result in small voids that will resonate. And some flags seem to be more prone to sounding echoey than others, but it's usually sandstone rather than pressed concrete. So I wionder if it might be summat in the sub-base or sub-grade.

I'm trying to think of a reason why the godawful GeoFix could be responsible. The best I can come up with is the fact that it is so airy and less dense than the concrete flagstones, so there may be some sonic effect whereby a tap on the flag results in a change in tone being bounced out by the crap jointing, but I'm wildly speculating here.

If you do decide to re-point, it would be interesting to lift one of the hollow flags while you have the old jointing out, and see if you can spot anything in the bed or sub-layers that might account for the mystery soundings.

[Hamachi]

Thanks tony,the sub base is 150mm thick type 1 ,I also used a touch of sbr in my mortar mix and an sbr bond bridge . It's the first time in 20 years in the trade I have had this issue . What are your thoughts on weather point 365 .

[lemoncurd1702]

If the sub-base has sagged under the mortar bed (but the bed is forming a bridge) is it possible that the hollow sound could resonate from this. Suppose it depends on how thick the mortar bed is, it's a possibility.

[Tony McC]

Weatherpoint is one of the better polymerics, and if you want to use a polymeric, then it would be in my top 3, but when you look at the cost of any of the better-performing polymerics, I can't figure out why you would use them when a genuinely good resin mortar can be had for the same money or just a few quid more.

[lemoncurd1702]

Weatherpoint is one of the better polymerics, and if you want to use a polymeric, then it would be in my top 3, but when you look at the cost of any of the better-performing polymerics, I can't figure out why you would use them when a genuinely good resin mortar can be had for the same money or just a few quid more.

Don't need to worry about it raining with weatherpoint.

[Hamachi]

Thanks for the advice guys will give 365 a try and see how I get on will post again when jobs complete

[Tony McC]

Don't need to worry about it raining with weatherpoint.

But that applies to any of the good polymerics and all of the resin slurries!

It's not an unique feature of Weatherpoint, many of the latest generation polymerics use a water-resistant oil to protect the binder, so can be washed-in with impunity. Once the water has drained away, the oil begins to dissipate and the binder cures when exposed to air. This is how some of them can be stored underwater for a fairly long period.

Some of the less good polymerics do require dry conditions, but these are either re-formulating with the new oils/binders or they are dropping market share at an alarming rate.

With slurry resins, all of the ones I've ever seen or tested need water. Some incorpoarte it into the mix but most (and I'm struggling to think of an exception) require the pavement to be wet *before* applying the slurry, so rain is of no consequence. In fact, it aids the installation by weeting the slurry as it passes over the pavement surface.

[lemoncurd1702]

Right I see, I've never had any experience with resin mortars so will take a look at the relevant pages.
Are they grainy like weatherpoint or do they produce a nice smooth finish.

[Tony McC]

Different types/brands use different aggregates and so create different finishes. Most are grainy but rub-up smooth if you use a pointing iron.

[KLS]

As you are talking about pointing products, is the Larsen gunpoint that Steve sell any good? I can only guess it is as all his other products are fantastic!

[Tony McC]

It's OK. I'm not a fan of any of the gun mortars but only because they hurt me back and me knees. The good ones certainly perform as mortars, but it always seems like a lot of effing about to get the same result as I can achieve with a trowel.

I know some folk love them, so it's horses for courses.