Hi,
I plastered my ceiling a couple of months ago and was really please with the finish. However, I wasn't sure of how to correctly finis with the float, and ended up finishing with a wet sponge/brush. I no have to do a wall, and really want the smooth finish from the float. Any tips? Do you use it in the same way as a trowel, or do you put i flat onto the plaster, in which case, how do you prevent suction?
Bruc
-- littlehobo
I dont know whether it is right or wrong, but on the plastering course I went on, we didnt use a float for the skim coat.
The float was used to smooth off the undercoat, whereas the trowel was used alone for getting the final finish on the wall.
Tim
I'm a self-taught plasterer and while I'm sure other people will post better replies, I can at least explain how I do it, which is to say the best way I've worked out how to do it.
Basically, I heard somebody refer to "polishing" the plaster and this kind of makes sense - you're using the float to polish it. A float isn't ideal for this purpose, and that's where the technique lies. All I do is wait around half an hour after the plaster has been applied, and then, with a spray bottle of water, spray and glide the float over the plaster (if swift upwards arcing movements). Never move the float across a part of the plaster you haven't wet first because it'll drag and then be a nightmare to fix. Also, be prepared to clean the edge of your float every now and again if you pick up something whcih scars the plaster.
The goal is to iron out the marks by filling them in with wet plaster you collect on the float as you skim it along while polishing.
After doing two or three walls, I got reasonably good at this, but I still had to sand down afterwards when it was all dry. My problem was simply running out of energy - the wall was so big that polishing it all perfectly takes a lot of effort. I think the best policy is to start from left to right and remain calm.
HTH
In article , littlehobo writes:
Let's start by making sure we're talking about the same tools. A float is a wooden (or nowadays, often plastic) faced tool, usually rectangular. A plastering trowel is similar but has a steel face, and importantly, two long straight polished edges.
Floats are used for rendering, screeding, and occasionally for scratch (base) coat plaster. They are never used for finish (top) coat plaster. Trowels are used for all these too, but also for finish coat plastering.
So to answer your question, you polish off with a trowel. I've posted the details before, but I'll run through them again. Firstly, a new trowel is a swine to use -- it will have sharp edges and very sharp corners which even a professional plasterer will dislike, and a beginner will find very difficult to use. Traditionally, a plaster would give a new trowel to a renederer for a few weeks to get the tool broken in on sand and cement, i.e. edges polished up and sharp corners taken off, and also it gets the spring in the steel working nicely, which it doesn't from day 1. You can polish up the edges on a flat faced grinding stone or the flat face of a house brick (easier to find on a building site) by using a sawing action, holding the trowel edge at an angle against the flat face of the brick. This is also useful to repair a trowel if you get a nick in one edge. Drag the corners across the brick face to take off the sharpness. In use, they'll wear to become rounded, which makes the trowel easier to use. You might find digging through [grand-]parents old tools to find an old trowel much better than buying a new one, provided the edges aren't damaged.
As for the plastering, to start with you just get concentrate on getting what you mixed up onto the wall with complete coverage of the area you are doing with that load. Ignore ridges, lines, etc, as there's nothing you can do about them yet, other than move them around which is not useful. Having got all the plaster on the wall, make any adjustments to thin out any excess areas and fill in any deficient areas. Now you have to wait for the plaster to start going off a little. When it has, you will find you can go over the area and remove the ridges created by the corners of the trowel. You'll create an equal number of new ones, but they'll be a bit smaller (if they aren't, stop and wait for the plaster to go off some more). You basically keep repeating this process until the ridges are gone. What you must do is stop working an area of plaster when you aren't improving it -- it needs to go off some more and you will only damage it by working it excessively before it's ready. The biggest mistake people make is not leaving it alone to go off some more. If you are working a big enough area, then going over it cyclically might give each bit enough time to go off some more before you get round to it again. As the plaster goes off, you will have to press harder to have an effect on it, and you'll need to lubricate the surface with water, traditionally flicked on with a large brush, but I find a plant sprayer easier to use, not having years of practice aim with the brush. This action becomes the polishing process as the plaster becomes nearly set; the smooth trowel edge takes off the peaks of the plaster surface, carries them in the lubrication water, and drops them in the troughs. However, don't get too carried away -- you can polish up the plaster surface so it feels like a sheet of glass and its horribly tempting to do so once you get the hang of it, but you'll find you can't paint it afterwards. If you do go too far, you'll have to sand the surface and/or excessively dilute the first coat of paint, or you'll find the first coat comes off when you try to do the second coat.
As you already commented, you don't ever allow the trowel to go flat onto the plaster or it will stick, and you'll be very lucky to get it off without pulling the plaster off the wall too. (You'll probably do it accidently a few times, and have to repair the damage;-) The face of the trowel is only used to carry the plaster to the wall initially.
While on this subject, a friend asked me to order him on of these the other day:
Aside from being stainless, the edges are pre-ground, there are no sharp corners, and both axis have a very slight curvature to them. Very nice - made my plain cheap and nasty Wicks trowel look just that! (I think I will see if I can borrow it for the next batch of plastering I need to do)
It's probably very good. Marshalltown are the bee's knees for trowels anyway, but unless you're a professional, you might not notice the difference, except in this case for it being pre-worn-in. There isn't supposed to be any curvature along the long axis -- the long bracing support is supposed to prevent that (often it's shorter on cheaper trowels which means the edge does curve when you press on it and you don't get a perfectly flat sweep). During the wearing in, the steel develops a better spring curvature across the short axis, although stainless steel may behave differently in this respect. It's not clear to me how a stainless steel trowel would behave -- traditionally they are high carbon sprung steel and that could make quite a difference.
I will let you know if/when I try it...
Perhaps curvature is the wrong expression - more a slight turning up of the corners - hence you have a long straight side but less chance of the corner making a mark. Either way it is a very subtle curve.
Yup - it was more "springy" out of the box than my bog standard one (which has skim plastered a couple of rooms now). But then again it was also a couple of inches longer which may give it more spring anyway.
Its not unusual to "polish off" plaster with a flat trowel, rubbing the trowel in a circular motion without flicking/spraying water when the plaster is almost hard and dry ie final stage of working. It gives a flatter finish but is extra hard work and can make the finish too shiney.
Or as the very last task, run a damp paintbrush up&down then left&right over the surface. That will remove the shine just enough to allow the surface to be painted
Anna
~~ Anna Kettle, Suffolk, England |""""| ~ Lime plaster repairs / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____|
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.