School boy error

[Millington Deco]

Hi, Guys I've just finished a kitchen splashback and used some rapid set adhesive on new gypsum plaster but forgot to prime first. Will this definitely fail and if so how long before this will happen?

 

[Qwerty]

No, as long as the plasterboard wasn't dusty you will be just fine (assuming the fixing method of the tiles was correct of course)

 

[Dougs Third Go]

Geoff, it's onto plaster not plasterboard, I reckon you'll see the tiles popping within 3 months. Not sure how you forgot to prime though..

 

[Rich Midge]

Oh dear! This will deffo fail, could be as quick as a day or two. You may be lucky and the grout will hold it all together but imo you want to hold your hands up and put it right. I'm presuming you're new to the trade, careers are built on reputation.

 

[Qwerty]

Aaaarghh!!!! RTFQ Geoff!!! Yep, will most likely fail as the others (who clearly read your post properly) have already said. Sorry, I have been carrying, cutting & fixing gypsum plasterboard for the past few weeks and I'm brainwashed by the stuff at the moment!

 

[kimboslash]

Ouch! They are coming off sooner or later.

That is the reason we have prep sheets on our van - so no matter how absent minded we are first thing in the morning we still go through the same process each time.

 

[cone]

Op, a wee bit of comfort or you here, I did the same in my own house over a painted wall and 12 years later, they are still on and I was curious about them last year and I tapped every tile, no hollow noise and couldn't pull off the one or2 I tried it on. In theory they should come off but who knows, your tiles might just still be on a decade from now.

 

[Millington Deco]

Looks like I've cocked up my first tiling job! I originally had tub ady planned for the job but switched to quick set at the last minute forgeting to take the primer into account. I will defo put it right tho as I want to take on more tiling work, looks like more homework for me then. :-(

 

[Stef]

Prime everything then this situation won't occur again..

 

[Millington Deco]

Thats great advice Stef, cone I've stuck and identical tile with the same ady on some gypsum under my sink to give me some idea of the time scale to failure if my phone doesn't ring before then.

 

[White Room]

I've seen tiles on a gypsum plaster no primer and they remained for many years, yes they should have been primed though...

 

[cone]

I've seen tiles on a gypsum plaster no primer and they remained for many years, yes they should have been primed though...

I prime and scrape all my work but what is the technical info on why primer is needed. How is it tiles stay on the wall when primed and come off easily when not primed.

 

[Rich Midge]

Crystals form between a wet cement based mortar and dry plaster. Bizarrely, this doesn't happen the other way hence why you can skim over render. By no means a chemist but this is the best I can do!

 

[Stef]

As Rich says, you will end up with ettringite crystals forming with a cement based adhesive against a plaster substrate.
Priming will give a chemical key but will also create a barrier between the two to stop ettringite forming.
I prime everything I tile, plaster, plasterboard the lot.
Read the guidance on your bags of addy & it will tell you whether to prime or not.

 

[White Room]

I prime because of the high suction from plaster, the cement based adhesive losses the moisture to quick to allow it to cure probably.
Was informed from a bod from Mapei that ettringite is formed when moisture/damp is present.

 

[Dash J]

Bang on the money there white beam
Suction

 

[Rich Midge]

It was the guys at Instamac that informed me of the crystals, this is going back 14 or 15 years. Though I agree that suction is a major issue I can't see it being the be all and end all. A damp sponge across a skimmed wall would surely prevent the addy from skinning over or drying out too fast but wouldn't increase the overall bond. Somebody somewhere needs to experiment?!

 

[Dash J]

I prime because of the high suction from plaster, the cement based adhesive losses the moisture to quick to allow it to cure probably.
Was informed from a bod from Mapei that ettringite is formed when moisture/damp is present.

I think suction is the be all
In a laymans term you are stopping the substrate from being so pourus by priming

Plaster,no primer,suck then pop de bonded

If it was a case of crystals then surely if you primed bonding plaster which is probably one of the most pourus substrates then you could tile it!
Me personally I would never tile bonding plaster if it had umpteen coats of primer

 

[Rich Midge]

Agreed bonding plaster will wick away moisture at a rate of knots but is only an undercoat plaster so doesn't have the inherent strength to support tiles regardless of priming or not. No addy manufacturer would guarantee their products straight onto bonding. Like I said earlier, I'm certainly no chemist just expressing an opinion. Personally I live by the prime everything rule.

 

[Dash J]

Agree mate prime everything

 

[White Room]

Agreed bonding plaster will wick away moisture at a rate of knots but is only an undercoat plaster so doesn't have the inherent strength to support tiles regardless of priming or not. No addy manufacturer would guarantee their products straight onto bonding. Like I said earlier, I'm certainly no chemist just expressing an opinion. Personally I live by the prime everything rule.

Ok, a plasterer puts a finish on dry bonding that suck moisture out so the top coat is worthless, you can prime till the cows come home and it would'nt make a blind bit of difference.

 

[Rich Midge]

Ok, a plasterer puts a finish on dry bonding that suck moisture out so the top coat is worthless, you can prime till the cows come home and it would'nt make a blind bit of difference.

Completely agree in that scenario priming would be pointless but I don't really get the argument sorry. No plasterer would apply a finish coat to dry bonding. They either do it same day or they prime. If however a plasterer was to do this, the finish coat would be so full of hairline cracks and hollow sounding that no tiler would consider it a suitable surface to tile on regardless of priming or not.

 

[Aston]

There's a positive spin on this because the plus side is, the tiles are going to be very easy to pop off so you can always start again and this time prime..Bet you'll never make that mistake again)

 

[widler]

Completely agree in that scenario priming would be pointless but I don't really get the argument sorry. No plasterer would apply a finish coat to dry bonding. They either do it same day or they prime. If however a plasterer was to do this, the finish coat would be so full of hairline cracks and hollow sounding that no tiler would consider it a suitable surface to tile on regardless of priming or not.

I have never primed a high suction backing plaster in my life, suction is a plasterers friend [emoji41]

 

[swanman]

grout will properly hold it

don't worry worst things happen at sea:hurray:

 

[swanman]

this is getting very technical
sounds like you are are chemists not tilers

 

[Diggy]

Don't panic Millington , they aint gonna drop off tomorrow. I spoke to BAL about this years ago and the tech bod then told me you might get a prob in 20 yrs time.

Just from now on prime your plaster walls and try not to lose any sleep.

Diggy