# Forum Home Renovation Plastering  Any "Tricks" with Cornice "Butt-Joints"?

## Batpig

Hello Folks, 
When a "Butt Joint" in the Cornice along a wall is unavoidable due to the long length of the wall, do any of you do anything special to (try to) prevent the joint from cracking in the future?... 
I am using 75mm Cornices, and I was thinking of either: 
1) Carving little 5mm bevels into the front edges of the two mating pieces, and then filling the resulting V-Groove with Cornice Cement... 
or, 
2) "Back-blocking" the joint with a small arc of 90mm Cornice... 
Wadya'reckon? 
Many Thanks,
Batpig.

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## skot

Professional Plasterers on this forum may shoot me down but I wouldn't do a butt join. When I do a join along the cornice I would make the join a 45° mitre

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## PlasterPro

> Professional Plasterers on this forum may shoot me down but I wouldn't do a butt join. When I do a join along the cornice I would make the join a 45° mitre

  ^^^spot on if you are really worried  :Shock:  chuck a bit of cornicse cement behind the join and on the two mitres.

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## jimmijamz

What's the difference here if you butt join or mitre join? 
i haven't been able to find out why people have 1 preference over the other?

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## Rod Dyson

Yes it is better to mitre the butt join, but this is only usefull if you "butter" up the joint. the reason is that the mitred join will give you more suface area to stick together when you "butter" up the edges.  
I also put a large amount of cornice adhesive behind the joint up the wall and along the ceiling so the cornice sits in a bed of cornice adhesive. Over the top maybe, but I don't get cracks in the joins. 
I also use the butt end of my joint knife to depress the edges of the join slightly so the actual edge is covered with a mil or two of adhesive. If it is plaster cornice I would v the joint slightly, rather than having a full tight joint.  Note, v jointing is NOT the same as having an open joint. 
Cheers Rod

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