Plastering preparation advice

[marct]

Hi,

My sister has asked me to do a little plastering. The area is about 2 foot by 1 foot. It already has plasterboard nailed/screwed in by someone else. There is a 2-3mm gap that is as deep as the plasterboard all the way round.

My question is do I need to fill the gap with anything first or can I just use multipurpose plaster over the whole lot? Will it go off properly round the edge? Also any other tips will be great. I can plaster large areas but the course didn't cover fussy stuff like this.

Thanks
Marc

 

[confidentincompetent]

I usually use one coat plaster for patching. I just lightly damp the area, (others will use pva dilute, but clean water is what they used before pva came on the scene) wack on the plaster, level slightly proud, wait for it to go off 2/4 hrs depending on depth then damp and polish up. Important not to mess about with it till its set and bonded itself to substrate.

 

[Nestor_Kelebay]

I would apply a fiberglass mesh joint tape over the perimeter of the plasterboard panel. That'll reduce the liklihood of the plaster cracking over that crack.

Also, ALWAYS ALWAYS ALWAYS when doing any kind of plastering work, work with a bright light positioned close to the working surface but some distance away so that the sharp angle of the lighting exagerates the roughness of the repair. (both spread the plaster and sand it down under such critical lighting) The lighting will give you the ability to better tell where to put more plaster and how much more to add and where to sand it down more and how much to sand off to achieve a smoother surface to your repair.

When the repair looks "not too bad" under such critical lighting, it'll look perfect under normal lighting.

Then prime and paint.

Also, if you use a premixed joint compound, my limited experience with these compounds is that they come extremely thick because no one wants to pay for tranporting water, and the manufacturer knows that you can thin it yourself, but you can't thicken it should you need to. So, when I've used premixed compounds, I've often felt you needed the arms and wrists of a mountain gorilla to work with them. If you have trouble spreading a smooth coat of joint compound without getting blisters on your hands, don't be scared to mix some clean water into the compound. You should be able to spread it smooth relatively easily. If you can't do that, it needs to be thinned.

 

[Nestor_Kelebay]

You should also be aware that you can also buy something called a "curved trowel".

A curved trowel looks like an ordinary trowel until you lay it flat on a table top or sight along it's edge and notice that it curves about 1/8 of an inch along it's length. Thus, if you were to hold the trowel flat against the wall, it would form an arch with about a 1/8 inch gap at it's widest under the middle of the trowel. But, because you hold the trowel at a comfortable angle to the wall when spreading plaster with it, this shape allows you to spread a perfectly symmetrical mound of joint compound 11 inches wide by about 1/16 of an inch thick at it's thickest. This is plenty thick enough to bury some fiberglass mesh tape in, but not nearly thick enough for anyone to ever notice a "bump" in the wall, even with wall mounted light fixtures.

So, if you're starting to do plastering work now, then you might want to invest a little money in a curved trowel for those repairs where you don't have a factory recess on both sides of the joint to bury your tape in. Curved trowels are made precisely for such instances where your tape sticks out from the surface of the plasterboard. If B&Q doesn't sell them, just go to any place listed under Plasterboard, Wholesale in your phone directory. The wholesalers will sell you a curved trowel because they know most retail stores won't stock them because of the problems they cause when people can't distinguish between them and a lower priced ordinary trowel. (cuz the curvature is so slight)

 

[marct]

I'm a little confused. I understand what you are saying with the curved trowel etc. but I don't see how it will hide the join between the patched area and the existing wall. Are you talking about the technique used for dry lining where you just fill the joints of the plaster board, or are you talking about using joint compound on the whole area including the join?

I still can't quite see how I get a finish such that you cannot see the new plaster on the existing wall? This wall is an existing painted wall.

Please bear with me, the help is much appreciated.
Marc