plaster mix quantities

[bobbin_about]

As a mostly self-taught plasterer, I'm never absolutely certain as to what extent my mixing proportions of plaster:water are correct. Most times the mix is Ok but at other times it ends up too stiff. Could someone please advise so that I can do some calibration?

What I'd appreciate knowing are optimum volume (litres) and weight (Kg) of plaster per (say) 5 litres of water for

(1) British Gypsum Thistle Multifinish plaster

(2) Thistle Bonding Coat

Both litres and Kg would be appreciated as a cross check.

I've checked the BG web site but couldn't see anything relevant.

Thanks for any info.

[Chas]

As far as I recall you pour in X inches (or cm or mm as the case may be these days) of water into a bucket and whilst stirring, add the required ammount of whatever untill the required consistinsty is obtained.

So, in a nutshell, water first, solids last.

[Andrew Gabriel]

That's because no one mixes it up that way. You start with a clean bucket, and fill it no more than 1/4 full of clean water. You then keep pouring in plaster and mixing until you get the right consistency (and no lumps).

For bonding coat mixed up correctly, it will stay on the trowel (just) when you turn the trowel vertically, but will slide off if you give a small jerk. Finish coat is more sloppy, and should slide off the trowel when you hold it vertical. People who haven't done much plasting usually mix it up much too stiff, thinking it will run off the wall otherwise, but it doesn't.

[Weatherlawyer]

..if you wet the wall or if the wall is plasterboard

[bobbin_about]

//

Yes that's what I do, but - big BUT - I was shown a long time ago by someone who'd been started off by a bricklayer/plasterer but was also mainly self-taught. So I operate in a bit of a knowledge vacuum. Much of what I do is as a result of trial and error and inevitably things drift. Mixing consistently and correctly is my biggest bugbear.

Plaster manufacturing must be a pretty tightly controlled controlled process, so I assume acceptable mixing proportions should be specifiable to quite close limits. Knowing these proportions would eliminate a major 'unknown' and let me make occasional self-checks.

Any chance someone could very kindly note down the weights & litres used next time they plaster & post here please? It would be so helpful to me and, if my experience of getting going with plastering is anything to go by, helpful to most newbie plasterers too.

That's helpful, though separated from the plasterer and without numbers it's hard to be certain we see the same thing.

Thanks.