When plastering over old plaster there appears air holes about 1/16 inch. What causes this and how can the problem be solved? The plaster is a vener plaster 2 coat application. The mixture is well mixed and does not appear where there is no plaster.
thanks
Replies
It comes from troweling the wet plaster when it's too wet, if I remember. Has to set up more. Might be wrong on wet v dry, but pretty sure it's a timing issue.
To answer you question, I need to know a few things. What did you do to the old plaster to ensure the new plaster would not delaminate? Which veneer plaster did you use? Did you use a base coat plaster before using a finish plaster?
Your holes can be caused by too mush moisture and troweling as suggested or from too much suction (too dry) where the plaster was not back troweled when applied.
We always use Durabond for a bonding agent. Imperial basecoat and Structo-gauge mixed with lime for the finish coat.
Sam
Thanks for the responding. The plaster was Imperial Interior Finish plaster. The base coat was brushed. Any advise?
thanks
Kind of suprised you are using Imperial Special White finish. It is the only all gypsum finish and also the strongest. It is also the least user friendly in some ways. You said the basecoat was brushed. What was the base coat and what did you apply to the old plaster to ensure the basecoat would not come off? If the basecoat was too dry and or the brush grooved the base too deep that would make it more difficult to prevent air from being trapped. Did you get the holes as you first applied the plaster? Did you double the coat from the same mix? You should always double the application and trowel in both directions which helps fill those voids. The other possibility is you have blisters from too much water in the base and finish. Also over troweling can add to blistering. It is my experience that Imperial finish, like Diamond tend to blister easily over base coats. That is one of the many reasons we long ago switched over to Structo-gauge and lime.
Sam
What brand do you like to use? They sell different kinds of plaster. What do you like for a single application and a double application?
thanks
Jeff, We use Structo-gauge job mixed with Ivory Lime which we mix at least a day ahead. We use only Imperial basecoat because it has the highest strength (#3000 psi) of anything available. The Structo-gauge can go on a bit thicker than the veneer plasters and it can be blended which is impossible with Imperial finish and very difficult with Diamond. It also gives you a lot of fat while you are wet troweling and the fat is more useful longer into the setting period. If you get fat from Diamond late in the set it is to milky and will not harden the same as the rest. Structo-gauge fat is all good and if you have a ding or imperfection you don't get to till its too late, just mix a little gauge podwer into your fat, works great.