How to attach cornice - cement or Liquid Nails?

Question

The ceiling material looks like some medieval plaster / mdf type hybrid board and the wall is cement render. After removing the cornice, I am not sure what adhesive they used originally, maybe standard cornice cement but a very thin bead as can be seen on the wall. On the ceiling no adhesive shows because I scrapped it off and sanded.

I was thinking as the ceiling is not a modern gyprock plasterboard and the wall is render cement, I should use Selley's Fast Grab Liquid Nails to be safe. I dug a deeper hole in the ceiling board to see what it was made of (see 2nd photo white part on the brown paper) it has white powdery (plaster) inside. So I assume it is some form of hybrid mdf type board and plaster? Googling has confused me a little. From the photos what would professionals use as cornice adhesive in this case for standard 90mm cornice / coving?

Thanks.

MitchellMc · Answer

Keep us updated @AusDIY and don't hesitate to reach out if you need further assistance.

Mitchell

AusDIY · Answer

Thanks for the detailed reply Eric. Ordered the Gyprock Masonry Adhesive.

EricL · Answer

Hello @AusDIY

My apologies, I forgot that you have a rendered wall rather than a plasterboard one. The Gyprock CSR 2.5kg Cornice Cement can be used on rendered surfaces, but a better alternative in this situation would be Gyprock CSR Drywall Masonry Adhesive, as it is specifically designed for plasterboard installation over masonry and concrete surfaces.

Your experience with the original cornice lasting more than 40 years certainly shows that clean, solid bare render can provide a very good surface for the appropriate adhesive. I agree that the slightly rough and porous surface also provides a good surface for the adhesive to grip onto.

My main concern is that very dry render can draw moisture out of the adhesive too quickly, which can affect how it cures and its final strength. This was why I initially suggested sealing the surface with Davco primer. However, I agree with your suggestion of lightly dampening the render instead. CSR also recommends dampening highly absorbent surfaces under severe drying conditions. In this case, I would not use the Taubmans 3 in 1 on the rendered section.

I suggest removing all dust and loose material first, then lightly misting the render with clean water so that it is damp but not visibly wet. You can then apply the Gyprock Masonry Adhesive and install the cornice.

If you've had a chance to look through the cornice installation guide, you'll also see why I prefer Cornice Cement or Masonry Adhesive over the Selleys adhesive for this particular job. Apart from bonding the cornice, these products can help fill small gaps and are much easier to clean up and manage if some squeezes out around the cornice. That's considerably more difficult to do neatly with a construction adhesive.

For the ceiling repair, yes, you can use the Taubmans 3 in 1. The repair sequence you've suggested sounds spot on, and I would proceed in that order.

In regard to the asbestos, I can only suggest having the walls and ceiling tested before you proceed any further into your renovation.

If you need further assistance, please let us know.

Eric