I've some smallish areas of blown plaster (house circa 1900) about 15 inches by 7 inches.
Whats the best technique & stuff to use to plug in the holes? [1]
TIA again!
Buzby
[1] I watched a professional plasterer at work once doing a ceiling. Total mystery as to how the stuff stayed up there, let alone ended up with a glass like finish!Are we talking ceilings or walls? Either way paint it with UniBond first and your chosen plaster or cement will have a good chance of adhering.
Fortunately it's walls.
I'll give that a spin - thanks!
Unibond it first. I once had an entire house held together with Unibond.
Plasterers are in league with the Devil and have sold thier souls to obtain the skills they have.
Dave
PVA bricks and the edge of surrounding old plaster. While thats still wet apply bonding coat to fill the hole then use a straight piece of wood to make it level with surrounding plaster. cut a small grove all around the perimiter say 1 -2 mm deep. Let it go off untill its firm say a couple of hours. Mix finish coat to a thickness that it will still slide off the trowel then apply to the bonding coat without going onto the old plaster. Let that get firm then trowel off and as you pull the trowel over the grove will fill and give a perfect match between the old and new.
One coat patching plaster. Instructions on the pack. Can't remember if it says to coat the wall with PVA first, but do it anyway.
Can you explain this "groove" thing a bit more. I'm not quite sure what you mean, but it sounds like a useful technique. Cheers, Happy New Yeat, Simon.
I take it you mean scrape back the perimiter like this?
_________ ########____,,--''@@@@@@@@@ ########@@@@@@@ N E W @@@@@ #O L D##@@@@@@@@@@@@@@@@@@@ #########@@@@@@@@@@@@@@@@@@
The most important and tricky part of a job like this is to make the join between old and new areas flush. You can't feather finish plaster into the old plaster because its quite course. Adding a groove allows you, at troweling off time, to spray on some water and pull the trowl over the join and this cleans the old plaster surface right to the join and makes the new plaster in the groove flush with the old. You wont see the join in other words.
Happy new "Yeat" M
Yes! ( I think)
I normally use the end of the float, or a wallpaper scraper, held at an angle to do that - next to the old plaster, scrape back to about 1/8" depth, sloping back to 0 depth on the surface of the new plaster (the ASCII picture isn't easy to interpret, this would be better:
This bit scraped out | v ______________ #### / #### / NEW #### / ####/ @@@@@@@@@@@@@@BRICK@@@@@
... if it was s t r e t c h e d so that the depth is 3mm, and the width of the scraped out bit is about 1 1/2"!!
Can you explain please why you remove only a perimeter groove of undercoat plaster - why is undercoat plaster not removed (for a two millimetre depth) right across the whole area of the patch?
I was wondering if removing undercoat from just around the perimeter would leave a raised area of finish plaster in the centre of the patch.
Regards.
Its not possible to get a flat surface that way. You use the surrounding old plaster as a guide for a straight edge.
The bonding coat shrinks very slightly as it dries, although if you use sand and cement that wont. Anyway the undercoat will be rough and at no point above the old plaster. The finish should be pretty thin and just smooths this off. The grove demarcates the border and makes it easier to keep the new finish off the old surface. Its not essential but quicker and easier.
For me the scraped out bit is usualy about 1/4 inch at the most. Do you make the edges of the patch straight?
No, just leave them as they are when the loose stuff's come off. Looking at my attempt at a pic. above, I realise it shows the plaster scraped back to brick, which it certainly isn't!
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