Cement slurries

[DNgroundworks]

Hiya Gents,

Back at work over the summer and we have some paving to do. The designer has specified 900x900x80mm sawn stone with 5mm joints.

I have used GFTK with joint sizes this small which looked great with a quartzite stone but i don't think it would look so good with the sawn stone. Im not a fan of the resin systems to be honest - too granular and it seems to green up pretty quick.

Im thinking of either Parex Granatech or the Instarmac flow point smooth, anyone used these, or something similar? Cost isn't an issue it just has to not fail. Planning on using a belt cleaner also.

Thanks all.

[lutonlagerlout]

WB Dan!
I hear you on the granular stuff but the 2 part resins are so strong, never really used slurry mixes,but would be careful on sawn stone
LLL

[DNgroundworks]

True LLL, i think i may reconsider and use a resin.

Another possible problem is that the GFTK mortars are permeable which makes me wonder of they are susceptible to frost damage. The product data sheet does require a permeable bedding layer but who lays flags like that?

Ive never had an issue with this, but why not?!

[dig dug dan]

More to the point dan, how are you going to manage to lay a flag of that weight and size???

[DNgroundworks]

Hi mate,

We have a probst vacuum lifter and brand new 5 & 8 tonne kubotas depending on reach, the probst should be suitable, laid some enormous copings with them.

If not we will buy the appropriate tool.

[dig dug dan]

I hav an al-vac that lifts 500kg, so i think the probst will be ok!
Had some 750 x 1000 to lay the other week. Side path, so couldnt use the digger without tracking over my work as passage was blocked one end. Only 32mm thick, but heavy enough to lay by hand!

[Tony McC]

GFTK mortars are permeable which makes me wonder of they are susceptible to frost damage. The product data sheet does require a permeable bedding layer but who lays flags like that?

Must have missed this last week - hope I'm not too late....

Frost? The 2-part resin mortars laugh at what we call frost in this counbtry. They are widely used in Germany, Scandinavia, Russia and lots of *really* cold places, not just countries that get a bit niuppy for a few days in January. They are practically immune to frost damage.

The permeable bed recommendation is because the mortars are intrinsically permeable, and so they perform best when laid over a free-draining substrate. When used with a typical British sand/cement bed, they tend to act as moisture reservoirs, which leads to them turning green with algae pretty quickly.

I wrote about this here

Power washing or use of a good quality biocide tends to control the greening, but use of a permeable bed really does make a HUGE difference, and becaiuse that method oif installatuion is pretty common in Europe, we see the recommendation on the data sheets for all sorts of jointing mortars made over there.

And as for asking who uses permeable bedding, the answer is we all will be using it, and sooner and you think, as it is more-or-less certain to be a requirement of the revised British Standard and will increasingly become a part of the "manufacturers' installation advice" that we are obliged to follow to ensure it's not our arse that gets kicked if paving goes wrong.

There are proprietary permeable bedding mortars, such as the truly excellent SteinTec TuffBau TuffBed, but a basic equivalent can be made by mixing around 300kg cement per cubic metre of clean 6mm grit to create a sort of Rice Krispie textured mortar/concrete.

I will be writing a LOT more about these bedding mortars in the years ahead. Like Garlic Bread, they *are* the future! In Germany and much of northern Europe, it's known as Trass bedding and that is likely to become the term we end up using, mostly due to their being no suitable, snappy English term that describes the mortar quite as well - why re-invent the wheel?

[lutonlagerlout]

think we have used concrete similar to this
no fines concrete?
it all sounds fabulous on paper, I like the 25 year test myself
LLL

[Tony McC]

Yep -in essence, it is a no-fines concrete.

[DNgroundworks]

No Not to late Tony, i think ill stick the resin, I'm familiar with it, ill speak to Carl at NCC if and when the job happens.

I find it amazing that the resin can withstand frost and the associated water expansion - i must admit I've never had to go back to a job.

Ive done a few decent sized jobs over the past few years between my studies - mainly york stone which i laid on 100mm of semi dry sharp sand/cement mix - could this be considered semi permeable or is it merely porous? EDIT - just read the page you linked.

The stone is coming up a fortune! The plan is to send a cutting list to our local quarry £££

[cookiewales]

No Not to late Tony, i think ill stick the resin, I'm familiar with it, ill speak to Carl at NCC if and when the job happens.

I find it amazing that the resin can withstand frost and the associated water expansion - i must admit I've never had to go back to a job.

Ive done a few decent sized jobs over the past few years between my studies - mainly york stone which i laid on 100mm of semi dry sharp sand/cement mix - could this be considered semi permeable or is it merely porous? EDIT - just read the page you linked.

The stone is coming up a fortune! The plan is to send a cutting list to our local quarry £££

I have never had any problems with resin 2part all my bedding 4/1 sharp sand cement which does drink some water