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Topic: Reusing bedding mortar?< Next Oldest | Next Newest >
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Posted: 16 July 2019,11:01 QUOTE

Hi everyone!
First of all a massive thank you to Tony and everyone who contributes to this site. I've never seen such a resource that is completely free and so detailed.
Armed with all this info I am making a stab at paving my back yard, so far I have dug out the clay soil, put in about 150mm of sub base, worked really hard getting all the levels and compaction spot on and so far it's been going really well.

To finish off I am laying 400x400 Tobermore Standard Flags which has been a steep learning curve from getting the mix consistency right (6:1 sharp sand, moist mix) to getting the bed right all before the mortar has went off in the wheelbarrow in 25° heat. Not a good time to learn I guess!  

So, as a result I have had some excellent results but some not so excellent and have had to bin some mortar as it became unusable due to the length of time I spent fannying about trying to get the flags level.

Then I noticed that some of the flags were loose and rocking. That was down to me not filling the corners of the bed fully or filling in finger holes in the bed. I've followed the advice on the site and have lifted the loose flags and installed new bedding.
Subsequently, I now have about two coal sacks full of a sandy, crumbly bedding mix. I was just going to take this to the dump but I read an earlier post about seiveing sand and using it so I just thought I'd ask the question as to weather it could be used again if the lumps were broken up and ran through a sieve? It's probably a stupid question as my gut is saying it's scrap but sometimes you just never know and I'm sure the answer I get will be the right one as you are the folks doing this day in day out and have seen the lot.  

One last question is can I add more water to a mix that is on the verges of becoming unworkable, stiff, crumbly or is it best just to scrap it and use fresh mortar?

Making mistakes is all part of the learning curve and I've thankfully improved my mixing and bed making considerably (with the help of a half flag with a threaded bar bolted and  bent into a handle as a means on checking the bed height before setting the flag).
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Tony McC
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Posted: 17 July 2019,19:02 QUOTE

Once mortar has "gone off" it's practically useless. It can't/shouldn't be re-wetted, as the initial hydration process has already happened and the result would be a far weaker-than-planned mortar.

Occasionally, it gets broken up and used as a blinding beneath a fresh mortar bed, or mixed-in with the sub-base, but it's days as a mortar are over. It seems a waste to send it to landfill when it cabn be used a fill aggregate (when suitably broken up).

If you are having adhesion problems, consider using a bond bridge slurry primer (can get messy!) or simply wet the underside of the flags immediately prior to laying so that they won't 'parch' the bedding mortar.


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Posted: 18 July 2019,10:05 QUOTE

Thanks for the reply Tony, you've pretty much confirmed what I suspected already. I'll put it to use in the sub base and the sandy stuff could be used for an area that I'm planning to lay artificial turf.

I've been using a SBR and Cement (1:2 ratio) slurry and it has been doing a great job in sticking down the flags that I didn't have to mess about with trying to get the bed right. I think the loose ones were the ones that I'd lifted a few times and by the time they were finally laid the slurry and mortar bed failed to bond as it had been disturbed so many times and the mortar missing from the corners provided the perfect leverage to break any weak bond there may have been.

Thankfully those days are now behind me and I'm able to lay a mortar bed with the most minimal of adjustments and it's now just a case of setting the flag and consolidating to its final level with no hassle. The white polythene sheeting from the flags is a great cover for the mortar in the wheelbarrow and for the newly laid flags to stop the sun baking off the mortar too quickly.

As it has been really dry and to try and avoid future adhesion issues I've been giving the back of the a spray of water from a pump sprayer, allowing that to soak in then applying to SBR slurry. That seems so stop it being sucked in to the flag and makes it flow just a bit easier. Is that okay to do?
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Posted: 19 July 2019,10:15 QUOTE

Yes - just be careful about accidental staining if the slurry becomes a bit too runny with the pre-wetted underside

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