BACK BLOCKING
Back-blocking is a method for reinforcing plasterboard joints to minimise joint cracking and peaking. The method for back-blocking is easy and I will explain how to do it in this article.
It is not necessary to back-block recessed wall joints, only ceilings joints and butt joints.
For those of you that don’t know what back-blocks are, they are off cuts of plasterboard that fit between the your trusses or metal batterns.
200mm wide minimum and 400mm length for (450mm trusses/metal batten) or 550mm length for (600mm truss/metal battern).
The Australian standard states that any joints that span at 600mm need to back-blocked. Joints that span over 450mm only need to back-blocked if there are over 3 ceiling joints in the room.
At Axon Plastering we back-block all joints regardless of truss/metal batten width to insure maximum strength to the joint.
You will find many plasterers will not do this and we urge you to always make sure your plasterers do this on your job. It is a common repair job done on many older homes as back blocks were not required on any joints many years ago. There is nothing worse then having your dream home crack within 5 years!
Method
Ensure the back of the plasterboard is clean and free of dirt and dust. Cut the back-block to the required size. (depending on width of truss/metal batten)
Using your 6”inch taping blade apply the back-block cement along the entire face of the back-block. You want to try and form a 10mm thick coat.
It helps to run the edge of the blade through the back-blocking cement to create a ripple which will ensure a better grip to the ceiling joint. Apply the back-blocking strip firmly to the back of the joint.
There are different ways you can back block your ceilings. If you choose to fix all your ceilings first, you will have to climb into the roof and apply back-blocks at the end. This can be a tricky if you have a small pitched roof. The alternative is to apply the back-blocks as you are fixing your ceilings.
Hang your first ceiling sheet. Once you have the first sheet finished you can apply the back-block half over the that existing ceiling. When you hang the next ceiling the ceiling sheet will grip to the back-block. This way is much more convenient.
It is important that you allow the back-blocks to set before you commence taping in the joints. We hope you endeavour to have your plasterboard fixed correctly to ensure no cracks in the near future.
Need more help? Contact us. We’re specialist Geelong Plasterers.