Skim coat on damaged plasterboard

by Albert
(Cambridge, UK)

Hello Paul,

I have a room which used to have some sort of washable paint. We have removed the paint - which was applied onto the plasterboard directly, but in the process we damaged the plasterboard in large areas. In some places the plaster core is exposed but paper damage is quite extensive. Reading your page and many other sources, I have a rough idea what I would like to do, but it would be very useful if you could comment.
- remove loose paper
- apply PVA or bonding agent (you suggested PVA with a bit of sand, is that applicable in this situation?)
- is it necessary to separately fill damaged parts?
- skim coat as described on your page.
Do you think this would work? Thanks in advance.
Regards,
Albert

Answer

Hi Albert,

It is difficult to provide a definitive answer but hopefully this will help:

1. Remove any loose paper
2. Apply PVA - when applying to any areas where the plaster core is exposed, ensure the PVA is not too thick, but is the consistency of skimmed milk, to ensure it soaks into the plaster rather than just laying on the surface. This will soak in fairly quickly so apply a liberal amount. Then with a slightly thicker mix of PVA (full fat milky consistency) apply a coat over the whole area - ensuring particular attention to areas where the paper is damaged.
If you intend to plaster immediately after the PVA has been applied (when tacky) then no need to add sand. Add the sand if you intend to plaster when the PVA is dry - the sandy rough texture will ensure a good bond.
3. As the PVA becomes tacky push some scrim into the PVA wherever the paper is damaged.
Where there is extensive damage, after applying plenty of PVA as above, a thin layer of Bonding Coat or Finish plaster can be applied to areas where the plaster is exposed. Scrim tape can then be pushed into this thin smear of plaster - plenty of scrim tape in various directions will add strength. Ensure any excess plaster is wiped off - so that the whole area is flat.
4. Skim as normal. (if there is a time difference between filling any damaged areas and skimming - then the areas you've filled may need damping down first)

So basically apply plenty of PVA and add scrim and plaster to fill as needed.

Paul