Plaster onto metal help.

knightstyle

So our 1980s house has wires and heating pipes in the walls covered by metal capping. The existing plaster has not stuck and is coming away.  I will chip it off and re-plaster but what can i use to make sure the plaster sticks to the metal?

FreeBear

Something like FeBond Blue Grit will help the plaster to stick to just about any surface, but... Hot water pipes will cause localised heating and the plaster will crack. Gypsum plaster does not do well if subjected to temperatures above 50°C.

Using a mesh scrim tape over the trunking will help to reduce the amount of cracking (I'd use a 100mm wide tape). A heat resistant plaster will help if the pipes do get hot - Be warned, copper in contact with plasters & cement will corrode, so the pipes need to be in conduit.

knightstyle

Thanks, that Febond looks like the stuff I need, wonder if I can get a small quantity, scrim as well if there is enough thickness there but some plaster is very thin over the capping. 
 The pipes are covered with tape where they touch cement and plaster.

FreeBear

knightstyle said: that Febond looks like the stuff I need, wonder if I can get a small quantity, scrim as well if there is enough thickness there but some plaster is very thin over the capping.

Smallest quantity of FeBond is 5l and that will go a long way. Scrim tape is cheap enough that even if you don't use a full roll, you haven't wasted a fortune. It also has the advantage that it works well under thin layers as well as thick. For an extra belt & braces approach, you could mix some 2.2mm fibres in with the plaster. But like the Blue Grit, you would only need a small amount, so hardly worth buying a bag..

Do you know any plasterers that you could hit on for small quantities of stuff ?

fenwick458

I'd say watered down PVA as a primer and Drywall adhesive will definitely firm it up.
are you skimming the whole wall or just patching up?

knightstyle

Thanks, yes I have found a spray of watered PVA worked well in the past, it was just the metal I was worried about.  Just moved to a new area so haven't got to know any plasterers yet. I will probably use adhesive scrim.
I an not that good at plastering so will just make good the bad bits.

knightstyle

Just finished sanding after my botched plastering but the adhesive scrim worked really well.
Thanks all who helped.