Do I REALLY need to prime concrete blocks before dot and dabbing?

[Thorfun]

it seems opinions on the web differ. some say PVA, some say a Plastering Grit, some say just soak the concrete blocks with water and some say don't bother with anything! what's a person to do?

 

they are new blocks (although the walls were built 4yrs ago) so it's not like they've got old plaster or render on them or paint or anything.

 

it's not a large area either with a small area around a door, a short wall (800mm wide) and in a cupboard under the stairs. do I REALLY need to prime?

[crispy_wafer]

Wipe em down, get rid of any dust/loose material, a bit of moisture on the wall will slow down any moisture transfer from the adhesive, which may or may not help… depends on how loose the mix is, with mine some walls i damped down, some I didn’t, looks like it has made no difference to the end result.  In your case I’d probably not bother. 

[Oz07]

Mix a blob of adhesive up, dab a bit of board on and try to get it off in a week. No prep required usually. If excessively dusty give it a brush. I certainly wouldn't be wetting it immediately prior. Might be hard to dab the boards to a straight edge

[Thorfun]

1 minute ago, Oz07 said:

Mix a blob of adhesive up, dab a bit of board on and try to get it off in a week.

No time for that! Want to get it finished this weekend so I can tidy up next weekend for the plasterers the week after. 😉

[Nickfromwales]

Avoid that Sineat(?) adhesive. Was getting sucked dry in no time, and boards weren’t staying stuck to it if any open time had been introduced. 
 

Switched back to Gypsum and totally different results. Client bought Sineat stuff as it was the path of least resistance, but even their plasterboards were shit in comparison.

 

If a roller dipped in 50/50 SBR/water solution, put on with a shaggy roller is cheap and simple, then I’d say sizing the walls the day before to bind the surfaces would be a no brainer. Not exactly something you can revisit, is it?

 

Don’t get lazy now, get your finger back out and put in the time and effort 🫡. SBR is cheap enough, and can even be applied with a Hozelock spray bottle that you pump up, but you Siri need to take a soft brush to the wall (hence the roller application as it kills both birds). 

[Thorfun]

1 hour ago, Nickfromwales said:

Avoid that Sineat(?) adhesive. Was getting sucked dry in no time, and boards weren’t staying stuck to it if any open time had been introduced. 
 

Switched back to Gypsum and totally different results. Client bought Sineat stuff as it was the path of least resistance, but even their plasterboards were shit in comparison.

 

If a roller dipped in 50/50 SBR/water solution, put on with a shaggy roller is cheap and simple, then I’d say sizing the walls the day before to bind the surfaces would be a no brainer. Not exactly something you can revisit, is it?

 

Don’t get lazy now, get your finger back out and put in the time and effort 🫡. SBR is cheap enough, and can even be applied with a Hozelock spray bottle that you pump up, but you Siri need to take a soft brush to the wall (hence the roller application as it kills both birds). 

Interesting how that I’ve had 3 responses and there’s still no real agreement! 😂

[crispy_wafer]

Haha, used siniat boards and adhesive 🤣, no problems, had a bag that was slightly out of date, that stuff went off quicker than Usain Bolt and the board didn’t hold, but that was me being a tight git, rather than the materials!

Edited 9 hours ago by crispy_wafer

[crispy_wafer]

44 minutes ago, Thorfun said:

Interesting how that I’ve had 3 responses and there’s still no real agreement! 😂

If you’ve any doubt, you’ve got nothing to lose by sizing the wall with a splash of sbr and water, it certainly won’t harm the job.   IMO The mix of adhesive is the biggest factor.

[Thorfun]

1 hour ago, crispy_wafer said:

If you’ve any doubt, you’ve got nothing to lose by sizing the wall with a splash of sbr and water, it certainly won’t harm the job.   IMO The mix of adhesive is the biggest factor.

Sure. And I’ve thought about just mixing up some PVA but I wanted to get it finished tomorrow and if I have to paint it on and let it dry then that won’t happen! 
 

I’ll sleep on it and see how I feel in the morning.