Plaster joint paper bubbling when wet!

[McBrain]

Hi Guys,

I'm new to this, but I'm following the Boral guidlines on joining butt-joints. On one joint I have done I have found that the paper has bubbled and even with the second basecoat the bubbles are still visible.

The procedure I useed was:

-Filled recess with basecoat.
-Placed paper tape on joint and smoothed out with trowel, ensuring no air was under the paper.
-Added a second coat of basecoat over the top staight away.

After a few minutes I found that some parts of the paper had started to bubble, as if because one side of the paper was wetter than the other. (the plaster consistency was ok)

My question is: How can I aviod this happening?
and, Is there anything I can do to fix it? the second basecoat didn't help. Do I need to rip the joint up?

Cheers

[OBBob]

Hi McBrain

Have you had a read of Rod's web site ... it's very uesful and I think it covers exactly this from memory.

http://www.plasterbrokers.com.au/

[McBrain]

Got it! Thanks.

I hope it's ok to reproduce this here for others' benefit?

Recessed Joins

Apart from being the strongest tape, it is also the most difficult to use for the casual DIY. The main difficulties experienced are bubbles showing up after painting or tape showing through the join, requiring the join to be over filled to hide the tape.
Bubbles forming under the tape, is caused by either no base coat under the tape, or the base coat has not been applied consistently and has dried out in parts before the tape has been embedded.
To avoid this, your mix needs to be a bit "wet", (not runny). Make sure you fill the rebate with base coat, ensure no board or dry spots appear before applying tape. Bed the tape into the recessed edge using a 5" or 6" joint knife.

To avoid the tape showing through, first make sure there are no bumps in the board. If so, cut them out with a trimming knife. If cutting out the bump creates a large gap, pre-fill the gap and scrap back level before taping. Bed the tape tightly and evenly into the recess, use quite a lot of pressure to squeeze out base coat from under the tape. Use the mix squeezed out to apply over the tape. It is important that the back of the tape is "wet" with plaster. Try short sections at a time until you get used to it. Paper tape stretches, so once the tape is embedded, to finish coating over, start from the center and work to each end. Finally run through the entire join from end to end to smooth out any excess. Remember to scrape back the join after the base coat has set, before applying second coat.

Repairing Bubbles In Paper tape

Quite often bubbled paper tape will not show up until the job has been painted. It is a good idea to check the job for potential bubbles after the first coat of paint has been applied. The reason for this, is that the paper absorbs the moisture from the paint and swells. Because it is not laminated to the board the swelling causes it to lift away showing up as a bubble.
To repair the bubble, you need to cut around the outline of the bubble with a very sharp trimming knife. Lift the delaminated tape away from the join, (make sure you have cut right through the tape to avoid lifting tape that has laminated properly). Using the handle of a joint knife depress the edge of the cut tape slightly. There is no need to replace the removed tape, (provided it is only a small section). Repair the depression using cornice adhesive using a 3 coat system as described in patching a hole. Don't try to over fill the depression let each coat fill it out a bit more each time.

[rod1949]

I'm not an expert. But I'm in the process of flushing all the plasterboard in my new house. I've installed BGC plasterboard but using Gyprock jointing compounds.

On the advice from the bloke in the Gyprock shop I'm using self-adhisve mesh tape and one type of jounting compound that is used as the base and finishing coats.

The self-adhisve mesh tape is placed/stuck to the joints first and then jointing compound is applied. To date I have not had any problems.

[rod@plasterbrok]

LOL I will let you!!

Cheers

[rod@plasterbrok]

Rod1949 I have to say this for the benefit of others reading this post.

Fibre glass tape just does not cut it for ceilings. It is the weakest tape available and prone to cracking.

While your job may be ok the chances are that the next one will crack.

We do about 20 houses a month and if we allowed our contractors to use easy tape on ceilings we would be repairing 2 a month. It is just not worth the risk.

It seems to work ok for walls, I have only had one call back for walls cracking. However if it is used on butt joins over doors or window it WILL crack eventually.

Another certatainty is that it will crack if used on villaboard or in internal angles.

The guy in the Gyprock shop should know better! The trouble is very few of the guys in the shop are tradesmen and don't get to see the result of the bad advice.


Cheers

Rod

[Big Shed]

Rod, that is interesting. Are you talking about the self adhesive mesh tape?

My son had cracks in his ceiling and used this to repair them and they promptly cracked again within a few months.

So, you have told what not to use, now what do we use? And what is the best procedure for fixing ceiling cracks?

[mic-d]

Hi Guys,

I'm new to this, but I'm following the Boral guidlines on joining butt-joints. On one joint I have done I have found that the paper has bubbled and even with the second basecoat the bubbles are still visible.

The procedure I useed was:

-Filled recess with basecoat.
-Placed paper tape on joint and

Usually if the tape bubbles, you've pressed too hard bedding the paper into the basecoat. The best time to fix that is when it's wet! Now cut the bubble out with a sharp knife and fill it again.

Cheers
Michael

[echnidna]

I have cheated in the past.
I just glued the paper tape into the recess with pva then plastered over it when the glue dried. Probably a no-no but it worked for me

[OBBob]

Hi Big shed ... it's all on Rod's site. But you need to use paper tape, which is much more of a pain to use but it does seem to be stronger.

[rod@plasterbrok]

Mid-C the tape will only bubble if it is dry underneath or if you are taping over a gap (gaps should be pre-filled). The tape should be firmly set into the base coat. To get the excess basecoat out from under the tape.

To fix a crack in an existing ceiling the best product to use is WET & STICK PAPER TAPE. This stick like a postage stamp to the ceiling. It can be coated over with the minimum amount of build up than any alterternative. Fiberglass tape is not an alternative!!!! Ordinary paper tape or cotton tape are the only other options. When you are fixing a cracked join you need to trowell it off as you would a butt join. That is 2 trowel widths. Also see trowelling a butt joint on my web site.

I do not reccomend Wet & Stick paper tape for any other use as it will not fill cover gaps very well and that can also cause bubbles.

One last comment the bubbles in paper tape are much easier to fix after the plaster has set. Often they do not appear until the 2nd coat goes on. Not to say it can't be done wet, If I notice a dry spot straight away while it is wet I simple lift the section of tape and squeeze some mix under it where the dry spot was and re bed it.

BTW Bob surprisingly the pva glue will do the job quite well!! pre formed bulkheads are taped together using paper tape and PVA glue. But you would need to pre fill all gaps. No I don't recommend this method LOL.

Cheers

Rod

[rod1949]

Rod1949 I have to say this for the benefit of others reading this post.

Fibre glass tape just does not cut it for ceilings. It is the weakest tape available and prone to cracking.

While your job may be ok the chances are that the next one will crack.

We do about 20 houses a month and if we allowed our contractors to use easy tape on ceilings we would be repairing 2 a month. It is just not worth the risk.

It seems to work ok for walls, I have only had one call back for walls cracking. However if it is used on butt joins over doors or window it WILL crack eventually.

Another certatainty is that it will crack if used on villaboard or in internal angles.

The guy in the Gyprock shop should know better! The trouble is very few of the guys in the shop are tradesmen and don't get to see the result of the bad advice.


Cheers

Rod

Thanks Rod. Its not what I wanted to read.

The house is totally steelframed and I've back blocked every ceiling joint, so will the back blocking resist the potential cracking ? If it dosen't what's the repair method.

[McBrain]

I had a go at cutting out some of the bubbles last night. The plaster was dry and it was quite easy to do.

I did some more joins and didn't have any more problems, I think I used slightly more bascoat under the paper and squeezed out the excess, this seemed to be better.

I was advised that the perforated paper tape was easier to use (I haven't seen it), but I will carry on with the normal paper tape.

Cheers
Nick.

[rod@plasterbrok]

Rod1949.

Back blocking the joins will certainly reduce the risk but wont eliminate it.

We have a company policy to both back block and use paper tape on ceilings. No need to worry about it. Plenty of plasterers out there are using fibreglass tape on ceilings and getting away with it. Not every job done with fiberglass tape will crack.

The problem is some do.

Chances are your backblocking will resist future cracking.

Nick there is a difference in the quality of paper tape on the market, the main difference that makes it easier to use is the stiffness. Stiffer tape is much easier to use.

Cheers Rod