butt joins I have just finished putting up a heap of gyprock, not all the joins have recessed edges, some are butt joins without recesses. How do I go about fixing these joins without getting cracks ? thanks
If the joints are in the ceiling there is a product called RONDO B005. It is a length of metal that has a 2.5mm 'bow" in it. When the sheets are screwed to it the sheets conform to this bow and creates a depression to fill. The supplier I will be using has recommended them to me for the butt joins instead of backblocking with gyprock offcuts.
they are all walls, no ceilings. I have used a stanely knife and a chisel to make a recess, then used tape. This should work and not get any cracks later on. Hope so anyway
cheers
Hi johnny
It sounds good in theory, but creating a recess this way will promote cracks. The strength is in the paper face. When removed, the plasterboard becomes spongey and the movement results in cracking.
thanks Masterplasterer, would the paper I put back on the join re-strengthen the join. Are there any other alternatives ?
Masterplasterer no doubt knows his stuff, but you should also visit forum member Rod's site for all this info! http://www.how2plaster.com/Originally Posted by johnnyroberts
The butt done to manufacturers specs is very strong. And if it cracks, you should have a case to have it rectified. I would try laying the paper tape over the sections that were removed ie. beside the original tape. I hope this works, I have never tried.
I agree with MP here you will need to tape the entire area you have removed the paper from. Butt joints need to be trowelled out at least 600mm wide to have any hope of not being seen.
Very few plasterers I know even our own trowel up butt joints correctly.
Here is my method of trowelling butt joints.
I always prefill the join before taping, even when the joint is tight. The reason for this is that I want the tape to be as flat as possible to the board surface. Even a small opening will cause paper tape to swell a little, meaning that you need to fill over the tape more to hide it. This makes the butt joint sit prouder than is neccessary.
When I tape I make sure that I bed the paper tape in as tight as possible. With the taping coat I run an 8 inch joint knife down each side of the tape filling out the full width of the joint knife. I do not run throught the center of the join. If the 2 sheets are not sittng flat together and one is slightly raised, (which sometimes happens if the ceiling/wall is not quite level, or a stud is twisted), I will use a 10 inch blade down one side and not feather the edge. I just let the blade find the right level so the join is flat from the center for the width of the blade.
For the 2nd coat I use my 12' blade and run it centered over the join so that it only puts a very thin coat over the tape but it will put more on either side of the tape. This will show you how wide you will need to go to get the join flat. With the same mix and the 12" blade I then run down each side of the tape the full width of the blade but feather out the outer edges.
I use the same method for the top coat but will go out a bit wider on the sides to cover all the 2nd coat.
This method gives you the flattest possible outcome for a butt join. Not all joins trowell up the same so I may vary this technique a little depending on the join. Often I will cross trowel a badly set butt joint working from the center out to the edges. The principle here is to put the least amount of mud possible over the tape and yet still cover the tape, whille filling out the join as wide as is requried to get a flat finish.
These joins can be completly hidden if done correctly.
Cheers Rod
Rod,
Is it worth running one sheet 90 deg to the others so you have at least one recessed edge? and use shorter sheets upto this so in theory you will only have one butt join 900mm wide on the 7.5m width of the ceiling?
No keep all sheets the same direction. Having a butt edge against a recessed edge is not recomended. You should always keep recessed edges to recessed edges and butt edges to butt edges.
The reason for this is that it is much harder to stop this join flat. as the shrinkage rate is a lot higher on the recessed edge side of the join.
If i ever come across this situation when someone else has hung the sheets, I would fill the recessed side of the join so I started with a flat join before I taped then treat the join as I would any butt join.
Cheers Rod
thanks Rod Thanks Rod, I get the picture now, much apreciated.
Thats what we like to hear, the right advice, no short cuts, and a quality job to boot!
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