suction

[i_am_fubar]

Ok, I'm confused, I've tried to find this out with google. But I figure its best to just ask the question.

What does high and low suction mean when refering to bricks/blocks or anything else that is to be plastered?

How do you determine what is what?

Sam.

 

[Richard C]

The suction rate is the speed at which the background your plastering absorbs the water in the plaster; this affects the speed at which it will go off & hence the working time you will have. The absorption rate will depend on the material & weather or not it’s sealed or primed, for example with paint or PVA.

Thermalite blocks would be an example of probably the highest suction back ground your likely to come across; plasterboard or a wall painted with silk emulsion on the other hand would be an example of low suction background. As for determining what’s what, that’s down to experience but it should be pretty obvious from the material in questin; if in doubt, throw some water on it & see how fast it’s absorbed!

 

[noseall]

it is all about quantity of water absorption.

the rate at which a masonry product absorbs water has an effect upon the plastering materials being applied to said products.

any product that involves hydration for curing or setting will not bode well if that water is removed too quickly.

so much so that, a wall that absorbs water more readily than one that does not, is generally more difficult to plaster.

soaking a wall or using of pva are common ways of controlling suction.

 

[noseall]

doh! you pipped me Richard.

 

[i_am_fubar]

So, essentially. before plastering any wall. give it a good coat of dilute PVA (or a band name one if you feel the need to do so) to seal it and remove the chance of excessive water absorbtion.

Does the same go for morter? I read about pre-soaking somewhere. Any tips for mortering Thermalite blocks?

Sam.

 

[noseall]

Does the same go for morter? I read about pre-soaking somewhere. Any tips for mortering Thermalite blocks?

Sam.

what do you mean, mortaring thermalite blocks?