Thread: Plaster dust

Originally Posted by Groggy

..... This is my first attempt and it ain't a pretty thing. .....

Just wait til you've had a go at cement rendering..... much harder to sand back to flat before you paint it.

Hmm OZwinner I wouldnt rely on that for one second. Sanding is the most important part of plastering when using top coat type materials and 3 coat system.

Pollishing a join went out with fibro. You cant hide a plasterboard join by polishing (it leaves 2 very differents surfaces). Even when you use a wet sponge on the edges of the joint, some sanding is still required, no matter how well you trowled the join. Its the nature of the beast I'm afraid.

But I guess it comes down to the level of acceptance for quality by the indvidual at the end of the day. My eye for detail in a plastering job would be far more critical than most.

As for the dust issue. Posts above are correct plaster dust is a killer on vac's. Sweep up as much as you can prior to using a vac.

Cheers

Rod, if you are still about, I am using (used, nearly done) an all purpose mix.

What is the difference between that and the three other types you mention on your site?

Also, can you mix plaster and cornice cement to fill gaps? I am guessing yes, since cornice cement would cover plastered corners anyway.

Greg, wait for Rod's response for the good oil, but I do know that cornice cement is v difficult to sand, but good for gap filling.

The multipurpose mix you're using will most likely sand OK but don't fill gaps that are too large or it may not harden (happened to me when plastering where the old crystal cabinet woz)

Hi Groggy,

The all purpose compound is as good as any product as far as the stability of the finished product goes. The main difference between using an all purpose compound (pre mixed) and any of the plaster base coats is how it sets and how easy it is to work with and the cost.

It costs more to do an entire job with all purpose compound and the job will take longer. The reason is that an all purpose compoud dries rather than sets. For the handyman all purpose compounds are far more user friendly. They don't dry as hard as plaster sets, making it easier to scrape back or sand between coats.

Plaster based products set quite hard and need to be scraped back between coats just after the plaster has set, but is still damp. Making it a bit harder for the handyman to use. Plaster base coats set in about 45 to 60 minutes. If you don't use all you mix in that time you will waste material.

Cornice cement can be mixed with base coat or other plaster powders for the purpose of filling cracks etc. However the setting times and workabiltiy will change depending on what you mix it with. You cant mix cornice cement or other plaster powdered products with the pre mixed all purpose cements or top coats. Cornice cement used on carcks should be coated with a final coat of top coat wich is sanded, rather than trying to sand cornice cement.

For filling large areas with cornice cement, you can bulk up the mix using perlite or vermiculite. This works great! You can fill in quite large gaps with this mix. We use this instead of mixing sand and cement to run curved cornice insitu around curved walls.

Every type of powdered plaster products have their own characteristics based on the level of refinement, and additives.

The main differences are:
Setting time,
Setting method, (slowly thicken and set, set suddenly, set uniform, etc.)
Set, Hard, soft, etc,
Workability (runs smooth, drags, lumpy, etc.)

This is why different plasters are used for different purposes.

Blending one type of plaster with another to get a certain result is not a problem.

Stopping plaster, is very similar to hard plaster is is a third of the price of base coat. But impossible to trowell on plaster board. However when mixed 1/2 and 1/2 with base coat, can used quite effectivly to trowel external angles. When a job has a huge amount of externals, they use up a lot of base coat. In this case blending cheap stopping plaster with basecoat would save you money.

This blend is no good for troweling joins because it will drag a little. On an external that is not a problem.

Bit more info than you wanted, but others might find it interesting!

Cheers Rod

Rod, love the info, I'm an amateur plaster as I renovate alot and it's hard to get this level of detailed info,
as far as the plaster dust is concerned and using water, the trick is DETERGENT, it breaks the surface tension and so the plaster dust is aborbed into the water instead of floating on top. Drop a cockroach in the toilet, he swims, add a drop of detergent, surface tension breaks, he drowns and sinks. It has to be low sudsing. Karcher even make a special vaccum cleaner with a water bath that you add detergent to and the air is sucked VIA the bath, not over it. (I think it's a ds5500 or something like that, they are going cheap on ebay as Karcher charged too much, didn't take off, so stock is being dumped). Don't use high sudsing stuff eg bubble bath, shampoo, I've found front loader washing powder isn't bad. If you want the dry option, vacs by festo have a lever you push that cleans some of the dust from the filter (scraps along the filter) into the bottom of the tank whilst still in th vac, easy fix when pressure drops (yes I know, Festo is expensive).

I'll try the detergent and let you know how it goes - thanks!

Great info Rod, thank you

I'm just sanding the topcoat now and these are the things I've learnt.

You can hire a gyprock sander and vac from Coates for about $120 a weekend. Does a good job on the ceiling and walls, but you can't use it in corners or near cornice. Also you have to be light with it, as it can work through to the paper very quickly. Or it can take too much top coat off and leave a small indent at you joins. Either way the one I hired blew up after 30 minutes so I was reduced to hand sanding anyway. Although the vacuum did a good job, it did blow a lot of dust around the house as well.

Using handsanders isn't so bad, but you do need mask and goggles. I found it better to have drop sheets down and to have the whole house locked up (no through breeze). That way the plaster dust just drops straight down on the drop sheet rather than blow through the house. Once I've done a decent section then I just shake out the dust sheet and voila. (caveat: I have a yard which in such a state that plaster dust improves it - good for the soil)

I have found the foam block sanders to be great, particularly the ones with a bevel - great for getting into the corners.

Cheers

The sanding machines are best left to the experts in using them in my opinion. They take of too much in the wrong areas. The problem spots are where a join intersects with an external or internal angle and Butt joins.

They also create very fine swirling scratches that can show up in extreme lighting conditions.

This is only to mention a few areas to take care.

A flat hand sanding float is no doubt the best tool for sanding a join flat. You have the feel to know where it needs more or less sanding. Use corectly you can feel if a join is over or underfilled.

The foam blocks are best kept for use in the internal corners. When they are used on joins it can lead to a very pronounced joins, even though the edge of the join is feathered and looks great. The reason is the short block is not feathering the join all the way across. I'm finding it hard to explain here in words, but trust me it can make an otherwise good job very bad!!

Correct sanding is the most important part of the plastering process. I had a machine sander and sold it, prefering to be up close to my work and able to feel what was happening, to get a good result.

cheers

Onya Rod

Good to have trade input.

Originally Posted by ozwinner

If so.........
Not that Im a plasterer, but the technique is wrong.

There shouldnt be too much, if any sanding.

I know a plaster who never sands.

Al

A "PLASTERER" shouldn't NEED to sand, but a gyprock fixer has to sand to get the required finish. (Maybe gyprock professionals can sand less or maybe they just ARE that good )

Originally Posted by rod@plasterbrok

A flat hand sanding float is no doubt the best tool for sanding a join flat. You have the feel to know where it needs more or less sanding. Use corectly you can feel if a join is over or underfilled.

I agree and I'm NOT an expert As a some time renovator, I did my own gyprock fixing and did a good job overall. My problem was not getting the best "spread" of the joint cement and consequently had to spend more time and elbow grease in sanding

The PAINTER (me) fixed it

Originally Posted by MrFixIt

A "PLASTERER" shouldn't NEED to sand, but a gyprock fixer has to sand to get the required finish.

In our part of the world there are no gyprock fixers only plasterers. They do all kinds of plastering including fixing plastersheets to walls and ceilings.

And I too have seen plasterers fixing plastersheets without sanding.

Peter.