Forum: Flags and Slabs
Topic: Plasticisers, slump and evaporation
started by: Newbie paver

Posted by Newbie paver on 22 July 2019,09:51
Just a quick question for the cognoscenti...

I've recently learned that a plasticiser addmix works by adding microscopic air bubbles to the mortar to increase the flexibility and therefore reduces the amount of water required to achieve the required level of slump and workability.

Would I be right in thinking that if I were to mix mortar to the same slump without plasticiser, would that increase the working time of the mortar in particularly warm conditions?

My thinking is that the extra water added in place of the plasticiser would reduce the evaporation effect on the mortar and would therefore have a slightly longer working time? My guess is this would possibly sacrifice the initial flexibility that plasticiser gives but I'd be willing to put up with that.

Or am I looking at this from the wrong angle? I just thought I'd ask before I try this and mix a barrow full and realise that I was on the wrong track altogether...

Posted by rab1 on 29 July 2019,23:51
Your mix will be weaker,  the more water you add will affect the strength of the mix.
Posted by rab1 on 29 July 2019,23:57
Forgot to add that its a lot easier to work with if you use plasticiser.
Posted by Newbie paver on 30 July 2019,00:38
Quote (rab1 @ 29 July 2019,23:57)
Forgot to add that its a lot easier to work with if you use plasticiser.

Thanks for the reply Rab, I've come to realise that without the plasticiser I now know what a “dead" mortar really is! The stuff is just stiff and not easy to work with at all!

Thankfully now the temperature has dropped and I'm no longer fighting the heat in getting through a guage before it went off and I've went back to using a semi-dry mix, something that would be very similar to a floor screed type mix. I find it easy to use as it's screed-able (?) using a home made tool I knocked together from pallet boards where it uses the last laid flag as a profile to screed against and so far it has given me some pretty consistent results without having to resort to making a bed on a trial and error basis and has improved the efficiency of the project. I guess my biggest problem is that I set a very high standard for myself and it then takes a while to build the skill in order to achieve that standard of finish that I hope to achieve.
Getting into an efficient system of work, getting a mix right, getting the bed right and getting the flags laid to the correct level and angle all in a very limited working time it has been a lot more difficult than I would have hoped for and it has been a steep learning curve, along with working in a heatwave didn't really help matters either but with a lot of trial and error, a lot of patience and figuring out a lot of things that I shouldn't do, things I should be doing and doing things differently I'm now getting on a lot better.
As a DIY'er one of the biggest disadvantages is that you have little time or room to really develop the skill before producing your best efforts, even with all the best advice and methods detailed on this site it still takes time to put it all into practice and produce a result that you're happy with rather than a DFR job that you just knocked out as quickly as you could get it done.

Many thanks for your help and advice.

Posted by Tony McC on 31 July 2019,19:20
In over 50 years of working on sites, I've only even met one clueless eejit that genuinely thought working with an unplasticised mortar was better for him than resorting to a plasticiser.

I watched this clown struggle, genuinely struggle over a couple of hours, to build a dwarf wall with 'dead' mortar, all the while protesting that it was (allegedly) cleaner, quicker, simpler and cheaper. The wall he produced was a feckin' eyesore and he was one of the stupidest people I've ever met in any walk of life. A complete tool! And he wondered why, in his early 60s, he was *still* working as a one-man-band barely making a living from general building work.

Plasticisers are invaluable with all forms or mortars and concretes, but there is a limit to their benefits. As a young lad still serving my time, I worked alongside a so-called 'mentor' who thought the small quantity of mortar we needed to point the brick risers of a flight of steps would be all-the-better for being prepared using nothing but liquid plasticiser - no water, just "Feb" mixed with the sand and cement.

I was in no position to argue, even though I'd aready mentally marked him down as a F***witt, so I had to go along with it, and it was, almost inevitably, me that was sent back, minus the 'mentor' to rake out the crumbling mess he had slathered into the joints, and then re-point with a 'proper' mortar, while he was invited to seek employment elsewhere.

Learning that paving is not as easy as many like to think is another invaluable life lesson, and one I wish more non-professionals would learn before diving in and claiming "how hard can it be?" right before they balls it all up. I try to provide guidance and advice via the website, but how do you distill 4 years of apprenticeship and a lifetime of experience into a few web pages? Nothing, absolutely nothing, is as valuable as experience. The best way to learn is to have a go.....but accept your limitations, temper your expectations, and your next job will be so much better!

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