Has anyone ever successfully used just a simple NHL + sharp sand mix to bed flooring slates / tiles / flags? I keep seeing these specialist “lime-based” flooring adhesive / grouting products which mention mysterious “additives”. I’d like to use the NHL and sand I’ve already got on hand and avoid an extra expense and shipping time if possible.
- Thread starter aockenden
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Yes, I replied to someone in the last few weeks…
What you may need, is an adhesive for the tiles depending on what they are and how the underside surface is. Our limestone slabs were machine cut and almost polished on the rear, no chance of getting any purchase so a quick wipe of Unibond first.
We also left a nice deep bedding layer of 40mm as I laid the slab before we’d decided on slabs - depth and possible variation if we chose reclaimed, that could be easily taken up in the bedding mix.
Using lime mortar under limestone
Hi all I’m looking for some advice on how best to lay a mortar bed under limestone tiles. ’normally’ I’d say use a notched trowel for the adhesive, but assuming this won’t work with the consistency of the like mortar. Just lay a continuous bed of mortar the desired thickness then tap the...
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Lacan07
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I decided I'm just going to use my usual NHL mortar (dry mix + water) to bed some limestone slabs to create my hearth. I successfully did the same to
I capped my lopped chimney with some slate tiles and NHL mortar (3.5 dry mix + water), its fine. I also plan to use it with limestone slabs to create my hearth for the wood burner. I've got no time for those adhesives.
I have 'grouted' using putty mortar on what now amounts to quite a large area (over 20 square metres in all). My technique was basically to point the tiles (some limestone flag style and some terracotta) with the mortar once they had been fixed, as if it were a brick wall on the floor. I have to say it was a big pain the *&%^ compared with the usual method of grouting with a slurry. There was the keeping it misted as it cures and the beating with the churn brush and all while kneeling on the floor. The result, however, was very pleasing. I was a little worried that the mortar might shed aggregate as people walked over the floor, but that hasn't happened. I fixed about half the tiles with seciltek lime-based tile adhesive(which contains 'additives' and behaves very much like a standard cementitious adhesive), most of the rest with NHL 2 mortar and for the smallish (about 2 square metres) hearth area with putty mortar. All have been fine.
Ok so I’ve got rough-backed reclaimed slate floor tiles. About 10 mm thick. Backsides are not only intrinsically rough but also have bits of old cement still stuck to the backs (which I’m happy to leave as extra key). So you used just NHL and sand for the actual bedding mortar?
Thanks that’s great info.
Ok cool this has all made me quite comfortable with skipping the modern stuff and keeping it simple. Thanks all!
Lacan07
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I had a chat about this subject with a chap who's extremely knowledgeable about lime and we agreed that NHL is fine for this kind of work because of its superior strength and structure, as opposed to using lime putty based mortars which I wouldn't use. Its a subject I'd been curious about as I'll be creating my hearth soon.
I just built a raised hearth as well and honestly I bedded a lot of the interior parts with cob. It only needs a small woodburner and it’s hardened strong enough now for me to stand on it without issue.
Flyfisher
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I don't see why there's any need for anything particularly 'adhesive' when laying a stone or similar floor. As long as things are properly bedded in then where are the flags/tiles going to go? External block paving isn't 'stuck' down and is only grouted with kiln-dried sand, yet with proper sub-base preparation it is perfectly solid enough, even to the extent of being able to support vehicles (I'm not advocating that approach indoors, but the basic principle applies, I think).
But to be more specific . . .
. . . yes.
We had a room with pamments laid directly on earth (so already, no need for anything 'adhesive'). I took up all the pamments to install a foamed glass/limecrete floor with wet UFH, raising the floor level slightly at the same time. The limecrete slab was about 80-100mm thick. I then re-laid the original pamments (supplemented with some reclaims to replace the broken ones) by bedding them into a thin layer of NHL2/sharp sand mortar. Finally, I grouted the pamments using the same NHL2/sharp sand mortar mix.
This was a couple of years ago and none of the pamments have come loose, even with the heating/cooling cycles of the UFH.
But to be more specific . . .
. . . yes.
We had a room with pamments laid directly on earth (so already, no need for anything 'adhesive'). I took up all the pamments to install a foamed glass/limecrete floor with wet UFH, raising the floor level slightly at the same time. The limecrete slab was about 80-100mm thick. I then re-laid the original pamments (supplemented with some reclaims to replace the broken ones) by bedding them into a thin layer of NHL2/sharp sand mortar. Finally, I grouted the pamments using the same NHL2/sharp sand mortar mix.
This was a couple of years ago and none of the pamments have come loose, even with the heating/cooling cycles of the UFH.
Great thanks, I’ll do the same then
Here are our 50mm - 75mm thick yorkstones bedded down using NLH5, builders and a lttle sharp sand. Sharp sand only would make them very hard to bed down. Make a slurry with the NLH5 and wipe the back of your flags with it. We are 3 years in with no movement.
Flyfisher
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After opening up an original inglenook many years ago I installed a new hearth onto the earth floor. It was about 8 inches deep from memory, which would have required quite a bit of mortar so I made up a 'ballast' mix of NHL2, sharp sand and LECA pellets (I:2:4 from memory). I then finished it off with clay pamments bedded and grouted with NHL2 mortar. I then installed a fairly large boiler stove (hence the copper pipes), which is used on an almost daily basis throughout winter months. This was in 2013 and there have been no problems so far.
Excellent, really beautiful stone floor, but what is that a portal to Hades in the floor?
Wait, did you find some way to run underfloor heating with a back-boiler wood stove? Or are they two isolated systems in your house?
Flyfisher
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Semi-isolated systems. Basically a large hot water tank with multiple internal coils. A mains gas boiler dumps heat into this 'heat store' via one of the coils and the boiler stove dumps heat into it via a separate coil. The boiler stove also connects to an upstairs radiator so that in the event of a power failure and the pump sending the hot water to the heat store stops working, the heat from the boiler stove can be safely dissipated.
Another coil extracts heat for the central heating system, which is (currently) divided into three zones for downstairs radiator, upstairs radiators and the UFH. Finally the DHW is fed from another coil. All the coils are at mains pressure except the one connected to the boiler stove, which has to be a vented system. The heat store itself is also vented. I also specified a spare coil to allow the possibility of solar thermal units, but have not yet utilised this.
It all works well enough, although as our renovation has progressed and more rooms have been connected it does struggle to heat the entire house, but this is a relatively rare requirement, which could be simply (albeit expensively!) addressed by replacing the gas boiler for a larger one. Besides, we also have wood stoves in the other reception rooms (and one bedroom) that we use when we have house guests.
That'll be a 7 meter deep well that the conservation officer insisted that we keep covered up with a stone gatepost. Thank goodness for the appeal system.
My goodness, this multi-coil, partially vented system was a thought I had as an attempt to keep our back boiler woodburner in the mix while still using a convenient modern boiler, but I cannot for the life of me find a plumber who is capable of even understanding, much less implementing, such a system.
Where did you find your plumber?