gypsum and cement based adhesives

[devonmark]

We all know that you should prime a plastered wall when using cement based adhesive to stop reaction...well as I was plastering a wall yesterday it got me thinking (yes painful, especially as I had a hangover), I had done an internal render of sand and cement and was going over it with multifinish..a gypsum based finishing plaster, what I was thinking is....why do I not get a reaction as it's gypsum over cement :huh2:

All the best to you all for the coming year..Mark.

 

[grumpygrouter]

Good question, not being a plasterer, I have no idea!

Grumpy

 

[DHTiling]

Good question mark...
I would have thought this would be best answered by a plasterer and not tilers....
So come on all you plasterers what do you think on this one.....

 

[devonmark]

I am a plasterer and do not know the answer....lol

Never even give it a thought til yesterday.

 

[Perry]

Mark i have been pointing that out for 25 years haven't found an answer yet and for twenty years i never primed plaster when using cement based adhesive without one failure if you find the answer let me know mate
Regards Pete :yes: :lol:

 

[grumpygrouter]

Maybe the best people to interrogate would be the adhesive manufacturers!

Grumpy

 

[Perry]

Grumpy tried that i think you will get the same answer don't get me wrong you can get a reaction between the two but its something they have always done but i think may be the plaster manufacturers would be the ones to answer the question

 

[devonmark]

I think I may fire off an e-mail to B.G and see what they come back with...

 

[DHTiling]

I think that once the cement has cured then there wouldn't be a reaction once gypsum is applied....let us know mark....i have crawled the net but can't find a deffo answer....

 

[Perry]

good one Mark i try not to think when i have a hangover :lol:

 

[devonmark]

Pete..likewise but as I was working alone in an empty house with no radio, I had no option...lol,

Dave, when going over s&c render you do the laying on of the render in the morning and go over with the skim in the afternoon or the following day therefore the render hasn't cured...mindboggling eh..pmsl.

Mark.

 

[DHTiling]

Would a lime based render be better than a portland based one.??

And how long does it take for the portland based render to fully hydrate.??

so that it can be skimmed with no reaction....so to speak..

 

[devonmark]

Would a lime based render be better than a portland based one.??

And how long does it take for the portland based render to fully hydrate.??

so that it can be skimmed with no reaction....so to speak..

lime based renders and plasters are breathable and therefore wouldn't be closed in with a gypsum finish

As for the portland question the answer from me is......PASS !!!!

 

[DHTiling]

we will wait and see B.G have to say ....cheers mark...