Understanding how porous a surface is.

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georgechapman

georgechapman

New Member
I'm just starting out so don't have the experience that many people do. I hear a lot of talk about how porous a wall is, preparation and plastering time but I'm yet to find a good explanation as to how to know how porous a wall is.

I get that a cinder block is very porous and a gloss painted wall is non porous but what about everything in between: new plaster, old plaster, emulsion paint, silk paint etc.

As I gain experience, is there a sure and fast way of testing the porousity of a wall I'm going to work on?
 
Brilliant, thanks Jess, and sorry for the dumb question follow up but is there a time by which I can guage porousity (if that's a word). Obviously it would not be absorbed into a gloss paint but something like an old plaster or even new plaster it would absorb slightly with some water on the surface for say 2 or 3 minutes; is the classed high suction or low suction?

(I ask because I read of different preparation techniques for different suction and feel I need to draw myself some sort of chart!)
 
georgechapman said:
I'm just starting out so don't have the experience that many people do. I hear a lot of talk about how porous a wall is, preparation and plastering time but I'm yet to find a good explanation as to how to know how porous a wall is.

I get that a cinder block is very porous and a gloss painted wall is non porous but what about everything in between: new plaster, old plaster, emulsion paint, silk paint etc.

As I gain experience, is there a sure and fast way of testing the porousity of a wall I'm going to work on?
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Your going to be pvaing the wall anyway other than board or fresh scratched float and set.

So just observe drying time if it pulls in quick get a wiggle on if slow get kettle ready!
 
zombie said:
Your going to be pvaing the wall anyway other than board or fresh scratched float and set.

So just observe drying time if it pulls in quick get a wiggle on if slow get kettle ready!
Click to expand...

You don't PVA s&c?

Every day a school day.
 
georgechapman said:
Brilliant, thanks Jess, and sorry for the dumb question follow up but is there a time by which I can guage porousity (if that's a word). Obviously it would not be absorbed into a gloss paint but something like an old plaster or even new plaster it would absorb slightly with some water on the surface for say 2 or 3 minutes; is the classed high suction or low suction?

(I ask because I read of different preparation techniques for different suction and feel I need to draw myself some sort of chart!)
Click to expand...
It’s just a case of suck it and see. You’ll pick up a feel for it as you go..... I sound like I’m playing innuendo bingo here! On average a wall needs two coats of pva. Pva-ing will have the same effect as water. It will tell you about the suction. If it’s hanging it’s low, if you’ve just finished pva-ing the wall and it’s almost dry where you started the suction is higher. Can’t say more than that really!
 
Mirror mirror on the wall who has the flattest wall of all ....of course it’s you George Chapman

.....and so the story begins
 
JessThePlasterer said:
I have spent years compiling that detailed chart I’m not just going to hand it out willy nilly!
Click to expand...
Understanding how porous a surface is.
 
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