PVA Sealing.

[Biglou]

Hi everyone im new to the forum.

If you wanted to use bonding on a higher suction backround (lightweight blocks in this case), if you pva'd it and then left it for 24 hours, and then once before you bonded it. Would it stop the suction enough to prevent it cracking?

Or would it stop the suction just as much, if i DIDNT leave it for 24 hours?


Only ive got a bag of bonding which needs using up! But the wall is high suction and not low suction!

I hope you understand what i mean. And thank you in advance.

Big lou.

 

[Richard C]

Welcome Biglou; a couple of PVA seal coats the day before to control the suction, then PVA again before plastering as normal. Use at least 2 coats of Bonding to bring out to the required level regardless of overall plaster depth & watch carefully as it starts to go off, particularly the 1st coat. You may need to dampen it down a little & go over it again to prevent crazing but don’t over do the water; I always use an old kitchen spray bottle.

 

[Biglou]

Thanks alot for that Richard C, the wall is very flat and level and it good condition.

Could i therefore apply the bonding coat freehand? Or should you always use timber dots to get it perfect?

Many thanks for the reply Richard C, i am very keen to improve my knowledge from more experienced tradesmen.

 

[Richard C]

If you’re doing a complete wall then you will still need guide battens if you want it nice & flat. If just patching then, no, just use the existing level as your guides.

 

[NickB_99]

Hi everyone im new to the forum.

Only ive got a bag of bonding which needs using up!

Hi Big Lou - welcome to the forum

Just to clarify - your bag of Bonding that needs 'using up', it's not already opened is it?

 

[Biglou]

Hi DIYnewbee.

No its not open but is getting towards the end of its use by date!

Just out of interest, what would be likely to happen if you used out of date stuff anyway?

(I havent done that dont worry! ).

Im assuming one of you professionals know?

 

[Richard C]

Just out of interest, what would be likely to happen if you used out of date stuff anyway?

Depends how it's been stored but in all probability, it’ll go off on you very quick & in bad cases in just a few minutes which is not much use to anyone really. Bonding doesn’t seem to be as susceptible to damp as Multi but I don’t know about the other base coats. Mix up a little & see how quick it goes off but in all honesty if it’s that close to date at this time of year I wouldn’t hold out much hope if it’s been hanging around for more than a week in your garage. For the sake of a few quid, I would skip; it it’s not worth the hassle it could give you.

 

[Biglou]

Thanks Richard C for the invaluable advise.

I will mix up abit and see what happens.

This may sound like a stupid question but...

You plaster ceilings first correct?

So if youve skimmed the ceiling, but then want to float and set a wall.

How on earth do you go about taping the joints? Because if you tape them after youve floated a wall, then the tape will be half on the freshly plastered ceiling.

Or am i thinking too hard...?

Sorry for the extra question!

Thanks very much everyone who contributes!!

 

[1john]

umm, tape them before the ceiling, sounds like it may be a bit late now though.

 

[Biglou]

umm, tape them before the ceiling, sounds like it may be a bit late now though.

Hi John.

No its not too late! done nothing yet!

You tape them before you do the ceiling? So you put the tape half on the ceiling and then half on to the bare wall? (with no plaster on as you havent done the walls yet, as you do the ceiling first).

Im assuming you use jute tape then? But therefore how do you attach it to the plasterboard ceiling?

...Maby someone gets what im on about!

And thanks everyone)

 

[roughcaster]

Cut your lengths of jute scrim ,, mix up a drop of multi finish, and using a trowel, put a 2 or 3 inch band of it along the ceiling/wall line. Bed your length of scrim into the band of multi finish,, half onto the ceiling, half onto the bare brick wall. Bed it well in, and smooth it off, trying not to catch the trowel on the scrim,, then let it set. I've put a picture of a partly scrimmed internal wall corner (plasterboard),, plus i've used bonding coat instead of multi finish to put them on with,, but it'll give you some idea of what i'm talking about. When you come to plaster the brick wall, just give the jute scrimmed area along the top of the wall, a wet down with water and a drop of pva,, to cut out any suction. You can also tape it in with fibre tape if you don't have any jute scrim.

Untitled

• roughcaster
• 6 Oct 2008
• 4

 

[1john]

although very new to plastering i find the 4" fibreglass scrim to be better on corners, i found that the 2" would get snagged easy and pull away easier.

 

[roughcaster]

You have to be careful with both John. There's nothing worse than putting on a length of scrim,, then catching it with the trowel, partly pulling it off.

 

[roughcaster]

i find the 4" fibreglass scrim to be better on corners

I've just re-read your post John,, are you talking about 3"jute scrim,, (which i've used) being better on corners? I've not come across the 4" "fibreglass" scrim.

 

[Biglou]

Roughcaster!

Thanks again.

Not only do you understand my gibberish, you are also a plastering genius.