Getting a decent finish with plaster

[JOE]

HI THIS IS MY FIRST POSTING How does one get a FLAT good finish when plastering a block wall?. I have a SMALL area 6ft by 4ft to plaster and I have to join this area, to an existing plastered wall. I need to get a good finish as the area will have wall lighting.How can one hide thE join with the old plaster?. Its difficult enough to patch and hide small areas where there is lighting, but a long join seems impossible ?Any help would be welcome. JOE

[Ian Clowes]

Hi Joe

Welcome.

I haven't done anything quite that size , but here's what I'd do. I'm surprised noone else has chimed in yet.

So are you extending the already plastered wall, so it sets the level you need? Or are you plastering upto an internal or external corner that is already plastered? Or maybe you've lost a patch of plaster in a wall and need to make good into both left and right sides? I'll assume the former. You can adjust the below to suit the other variants.

Hmmm. Not sure my technique will be quite up to that.

I've found that the more ragged the old edge (within reason) the better. Whether this is because the two 'knit' better, because it removes any single weakness with the underlying wall or for some other reason I don't know.

So, if there's a good square edge I'd chop into it a bit to give a rougher edge. About 3" of raggedness is what I'd go for. Then brush this down dry and give it a good brush over with PVA and water mix to firm it up and seal it. Also give the base blocks a coat of PVA to seal them.

If your new blockwork is set into or against an older wall (such as blocking off an old doorway) I'd set some metal mesh into the plaster over the join unless the old and new walls have been stitched together well. This should help preven cracks appearing as the old and new surfaces shift against each other slightly.

Next I'd set 'battens' of 1/2" ply or something similar on the wall at

18" or so intervals. This should divide the area you have into 3 strips. For the same 'knitting' reasons I'd cut these to have a wavy edge.

Now fill the two outer sections with a base coat, and drag off using the ply strips as a depth guage. Let this set, and key it as it goes off.

Remove the ply strips, and fill the middle section with plaster. Drag this off using the two side bands as a guide. Key it again as it sets.

Now for the risky bit. Apply a finish skim, and work it to a level surface using a light to help spot highs and slacks. Let this set pretty well before starting to polish it. I always used to try polishing too soon, with undesirable results. I'm better at gauging when to do this bit now.

In terms of materials I've found one coat 'amateur' plaster from the likes of Wickes to work well for me as a two part system. You'd need to check waht was suitable for your blockwork though and might need something else to get a sound base.

I don't envy you doing this task, but having worked on smaller areas I am looking forward to trying a larger area (like you have) next time to see if I've progressed.

HTH IanC

[Anna Kettle]

Butt the new plaster up to the old, rather than feathering it out. Spend some time with a scraper to be sure the surface level is identical and with a damp paintbrush to remove stray wet plaster from the old surface. Then when its set you can fine tune with a bit of polyfilla.

For perfection, you should reskim the whole surface.

Anna

-- ~~ Anna Kettle, Suffolk, England |""""| ~ Pargeting, decorative and traditional / ^^ \// lime plasterwork |______|

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