Had a go, but why the cracks?

[wellerman]

Had a go at plastering with multi-finish on the toilet wall today (approx 4ft square area)

Initial panic set in when I saw it beginning to crack where it was drying out too quickly. Managed to save it by keeping it watered with a spray bottle and troweling across it but it took ages!

I did PVA the walls last week and then again just before starting the skim.

I'm quite pleased with the results - flat and smooth across 99% of it, but then it was only a small area.

Was it because I didn't make the mixture thin enough in the first instance that made it dry out too quickly? I had a smooth consistancy slightly thinner than a cement mix.
Does it need to be alot runnier to prevent this next time? I assume it does as I must have applied another litre of water to it when it was on the wall!!

And what it the best way of meeting ajoining walls/internal corners?

 

[Richard C]

It sounds like you may have experienced too much suction, what are you plastering onto? Equally, it could be the plaster itself – near date or badly stored will drastically reduce the setting time; over mixing/too fast with a mechanical paddle will also pull in air & shorten set time.

Difficult to describe the plaster consistency required, maybe like Mr softy ice cream, you should easily be able to shape it on the hawk so it maintains it’s shape, too thin & it’ll mostly end up on the floor, too thick & it won’t be workable; it will also stiffen a little within the first few minutes & then stabilise so you need to take account of this.

Managed to save it by keeping it watered with a spray bottle and troweling across it but it took ages! I assume it does as I must have applied another litre of water to it when it was on the wall!!

Adding more water to the mix once you’ve started is not good & splashing loads of water to the surface once it’s up will ruin the surface texture & it will dry into hollows with a powdery surface. I use an old 1 litre, kitchen spray bottle & will do a whole room with that & still throw some away.

 

[wellerman]

Hi Richard,

Was plastering over some render which appeared to be a sand/cement type. Used an electric drill to paddle mix - aware that it is too fast so used in short bursts.

The consistancy seemed OK, but as it began to dry too quickly either it was over-mixed or could have done with a bit more water.

Is it best to let it stabilise before commencing? I started to apply straight away as I didn't want it to go off. I was also afraid of over-working it by constantly over-trowelling, although as I say, with the extra water it seemed to work OK - don't want to get into bad practice though!

 

[Richard C]

Is it best to let it stabilise before commencing?

No it’s just something that happens in the 1st few minutes after mixing, just be aware & take account of it.

Render base is very high suction & can be difficult to control if not sufficiently sealed or you don’t damp it down enough. For skimming over render or when floating onto block work, I will liberally douse the walls with a garden hose & spray attachment.

 

[1john]

did you do two coatsb of finish?

 

[wellerman]

Just the one coat used as I just wanted a light skim over to level it up.

If applying two coats, after how long from putting on the first should you apply the second?

 

[1john]

when the first starts firming up, on a tiny area like you are doing, you can prob get away with having a cuppa, cleaning your tools and making a fresh mix.