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Posted: Fri May 28, 2004 5:01 pm
by Julian
We are currently laying yorkstone in our early 18th century yard, reclaimed in one section, new 75mm sawn in others.
I made a test mix of 1:3:12 Portland cement : NHL 5 Hydraulic Lime : kiln dried sand and experimented using this as a brush-in joint to fill the varying widths of joint we have between the flags (7 - 15 mm in the reclaimed, but the newer flags will be laid with about a 10mm joint).
I am pleased with its soft appearance (and the conservation officer is happy too - this is a grade 1 listed building) and it has hardened slowly over the past few weeks, so that it appears to be unaffected by rainwater, even heavy downpours.
What do you feel about this approach? I accept that it may be unconventional, but I would like to ensure that it is not quite simply wrong from a technical point of view.
May I add the comment, often seen in this forum, that this is a really excellent website, produced by someone who clearly has not only a passion for his profession but a love of sharing it with others.
Posted: Sat May 29, 2004 5:31 pm
by 84-1093879891
I think what you have done is fine - I have absolutely no problem with it.
Lime was often used in pointing motars many years ago and was only really supplanted by OPC because of the perceived need for a 'hard' mortar. However, for the type of work you're undertaking, I see no real need for a solid, rock hard joint, so keep on with with lime mortar!
If you can manage a few photies, I'd love to see the results. :)
Posted: Thu Oct 21, 2004 1:41 pm
by Julian
Several months later ... job done! - Or at least the laying of the slabs, which has been a great success (photos to follow).
I am having misgivings about the jointing method we discussed above, mainly because I cannot be sure the joints will ever be strong enough to take a pressure washer, and the yard would benefit from such occasionally (especially as large parts of it receive little sunlight for half the year). At over 150 square metres this is a fair area, and I am concerned that wet pointing may prove to be hugely labour intensive if done in the normal way.
Do you know if it is possible to pressure-inject a well plasticised mix via a narrow nozzle from a mortar pump? Or some similar method of pointing a large number of narrow joints in a reasonably short time.
Alternatively I wondered if the cracks could be "primed" with water before the application of a brush-in mix in order to ensure the optimum cement-water reaction. As I am well out of my depth here, your help would be greatly appreciated!
Posted: Thu Oct 21, 2004 9:47 pm
by Tony McC
How wide are the joints? Are they consistent, tht is, are the joints in the 'reclaimed' section more or less the same width as those on the 'new sawn' section?
There are pumpable mortars but the efficacy of the various systems ranges from 'bloody awful' to 'bloody impressive'.
The simplest systems, and the ones that tend to be the most trouble, are those based on some form of mastic gun with a site-mixed mortar packed into a cartridge. The mortar is squeezed out via the nozzle in the same way as would be done when sealing the tiles around the bath. The key to success is an additive that keeps the mortar fluid. Some a no better than a cheap wash-up liquid, but there are one or two that do keep the mortar in a workable condition for 20 mins or so, albeit at a price.
Then there are the power-pumped systems. These range from pre-mixed mortars fed into a hopper and pumped to the point of delivery via a lance, to those feeding a site-mixed mortar from a pan-mixer. These tend to be used on larger, commercial schemes, and rely on having a consistent joint width of 8-15mm, over a flattish area, with a joint depth of 40mm or so and no obstructions in the joints. The mortar is delivered as a slurry and flows from the delivery lance into and then along the joints. Some skill is needed to judge the flow of mortar, and to wipe up any spills or surcharges as they happen. Again, these are not particularly cheap.
A method that is often used on this type of project, where reclaimed materials from a numvber of different sources, or a mixture of new and reclaimed are laid, involves using a standard 4:1 mortar slurry brushed in over the entire pavement, and then sand-blasted clean when the slurry has set. It's a little more complex than that, as care is needed to remove as much of the slurry from the surface before it sets, and the sand-blasting is usually a job for a specialist, but it can sometimes work out a lot cheaper than using a pumpable mortar.
Over the past 18 months or so, myself and couple of contractors have been experimenting with a method of using retarders with a slurry, primarily for sett paving, and we feel we've found a methodology that works as well as it can. It's not 100% stain-free, but it's much better than washing off with water and less costly than sand-blasting.
It's also worth mentioning the pourable mortars. These are mixed as a slurry and delivered into the joints via a watering can. These tend to work well with wider joints, those of 12mm or more, and this sort of thing could well be the best option for your project.
Which of these sounds most appealing?
Posted: Fri Oct 22, 2004 12:41 pm
by danensis
I'm wondering if there is a real problem here at all? After all many of the lighthouses around our coast are built with hydraulic lime mortar, and they stand up to a bit more than a power washer.
Posted: Fri Oct 22, 2004 2:37 pm
by Julian
Thank you for all the various comments and ideas. I am going to experiment with a pourable mortar, because I think it would have the added benefit of ensuring that any voids are properly filled.
I quite agree with danensis about lime - and of course lime has often been specified for concrete permanently immersed in water - but my real concern was about using a dry mix, in which the hydraulic compounds might never gain their optimum strength as they do when they are mixed in advance with water. I am concerned that no one has said "Yes - this method really works".
Posted: Fri Oct 22, 2004 3:13 pm
by Tony McC
I've never used lime in a dry grout method. On ethe few occasions when we have grouted using a lime-based mortar, it's always been a wet grout.
Dry grouting only really works well when it's used in conjunction with a freshly-buttered joint. Adding a dry grout some time after laying, when the joint is dry, is never 100% satisfactory, I find.