Flat Plaster

Hi Paul

I signed up to your online plastering lessons to learn more about plastering (i'm still new at doing it).
I'm running in to a routine problem of getting the plaster flat, soon
as the first coat goes on I'm evening it out, but when it's dried I can see where it isn't flat.

Have you got any tips on how to avoid the issue?


Thanks
Darren

Answer
Hi Darran,

Doing these may help:

Ensure the plaster you're applying is runny and not mixed too thickly.

Ensure the depth is no more than 1-2mm

Use as big/long trowel strokes as possible.

Push really firmly (ensure correct trowel angle)

Don't play around with it - make sure it is as firm as it should be to get the desired results in each relevant stage


Hope these may help
Paul

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Mar 31, 2018
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by: Mark

Feel free to take on/ignore as much of this as you like, but ás someone who has recently been learning a lot the hard way, here is my 2 pennies worth that I hope might have something useful somewhere:

1) make sure the existing wall/ backing plaster is as flat as possible to start with. If you try to flatten everything with skim then you'll end up with the thinner regions drying out and becoming firmer faster than the thicker regions. Danger is that you start to flatten/ trowel when you think it's at the right stage, but the trowel sinks in to the thicker, softer regions. I'm sure with practice and experience it's less of a worry, but if you do spend the time filling in, and getting the substrate as flat as possible first, then you can save yourself a lot hassle during the skim coat.

2) still focusing on the substrate - be it plaster board, backing plaster, or whatever; make sure you not only control the suction with pva, but also that the suction is UNIFORM. If you've got patches of fresh bonding / different backgrounds, make sure you pva everything to give yourself a fighting chance. If you don't then any regions of higher suction will dry out faster, and essentially you'll be back in the same situation as (1).

3) apply the skim as flatly and evenly as you can from the word go i.e. on the first coat. Make sure you do apply in one direction and then flatten each and every 'application' stroke by going back over in the opposite direction and use enough pressure so the plaster is squeezed out along the full length off your trowel. Essentially, unless you do go go back over each 'application' then you can be pretty sure you won't get a very uniform thickness on the wall - no matter how carefully you try to keep the trailing edge of the trowel at a consistent "2mm" from the wall.

4) I've seen a lot of YouTube videos where people go straight over the first coat with the 'second coat'. If that works, then great, but I struggle with the science behind that a bit in my own mind to be honest, as I can't see a huge amount of difference between that and just doing one thick coat... but what I've found works for me is to do the first coat, wait a while to give it chance to firm up... flatten once with a plaziflex, and then go back over with the second coat. Say I applied two trowel loads to cover the height of the wall on the first coat, then I use one for the second coat - that way I know I'm using ~ half the thickness for the second coat.

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