Cracking Villaboard on ceiling (set)

Hi guys, here's da problem.

Outdoor verandah built with villaboard sheets running perpendicular to the joists (600 ctrs). basecoat 60 with a dash of milk was used with paper over the joints. Initially joints looked fine - a couple had to be patched (paper removed etc) after a day or 2, so then top coated, and painted. Now months down the track, the paper is lifting and maybe 40% of the joins (both recessed and butt) are showing with gradually worsening paper lift..

To give an idea, I also did the ceiling in the house, and that has all finfished fine, so the problem seems to be just villaboard as opposed to gyprock.

The question is, whether redoing with a different procedure (wide outdoor mesh as for blueboard perhaps), or just canning the whole idea and going for a bunch of cover strips?

With the cover strips, I'm supposing I'd have to remove all jointing material (gee wont that be fun) and allow the joint to open then glue cover strip - I was thinking of clear anodised al strip.

Currently wishing I went with my original idea of the wet area gyprock rather than the villaboard (builders convinced me of the vb!)............

1st problem. 6mm villaboard should only be fixed at 450 centers. (no warranty from the manufacturers here),

2nd when stopping up villaboard out side great care must be taken that the plaster acutally set as opposed to drying.

Villaboard itself sucks the water out of the plaster by adding milk you have extended the setting time. Therefore when the moisture is sucked out of the mix the air outside causes the plaster to dry. The plaster has not had time to crystalize so it is weak. This is what has caused the paper to lift.

You may find that the plaster is slightly powdery rather than rock hard.

Rip out the tapes and do it again it should be ok. Even with the 600 mm centers. Although if possible I would put some wid back blocks on the joins. If you can lift some tiles to get access.

When you a stopping up villaboard out side it is best the wet the joins down first to stop the water being sucked out of the mix. Also speed up setting time NEVER use a retarder. Better still use an all purpose compound that will dry rather than set.

Cheers Rod

Hi Rod - Mr dependable! ;D

gonna take some serious motivation for me to get round to sanding, grinding and scraping for a day above my head! I had a feeling that fast drying was going to end up been the cause - wondering if using an acrylic primer such as for tiles might help in the cause to add adherance and slow setting?

Strangely, I bought some gyprock 45 base a couple of weeks ago, and I'd swear that it sets slower than the 60 from boral - which is the one i ended up retarding with the milk - work time was < 15minutes - maybe I'm just better at mixing and using now - who knows!

Older plaster will set a lot quicker than new plaster. The quality of the water will also effect setting time.

Storage on concrete will effect the life of the plaster as well.

It is a common problem in warmer climates. In summer I only use the all purpose cement if I'm doing a large area and speed up the setting time with base coat or crornice adhesive if doing a small area.

Good luck with it.

Wow, I'm impressed.
We're going to have to start calling you "Professor" plasterbrok. :D
Have you done a degree, or have you got a lab in your basement, complete with mass spectrometer? :;