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Putting up a shelf plaster sounding hollow and cracking

Hi. Im trying to put up some shelf rails, they have 6 screw holes in each rail ( 2 rails)
Some of the drill holes i have made have made the plaster crack, some just hairline some plaster has fallen off. When i screwed the screw into the raw plug the plaster is again cracking and coming away.

Im worried some of the plaster has blown behind the rail and thats causing the problem. What is the best way to work with this without replastering the wall or not having the shelf there? The house is pretty old (1890).

I have been using general rawl plugs (3cm/4 cm) and some 7cm/8cm screws. could the problem be that the hole i am drilling isnt big enough for the rawl plug and the screw and thats causing the cracking or would it be the blown plaster? Is there any rawl plug that is recommended in this situation. What size screws should i be using?
The shelves are wooden about 2 1/2 foot long to hold books so it needs to be pretty strong.

Many Thanks for your time.

Additional question:

What sort of rawl plugs should i be using, having visited the hardware store there seems to be a lot on offer. Will the general purpose ones be enough of do i need specific plaster ones?

Thanks again

3 Answers from MyBuilder Painters & Decorators

Best Answer

you may need to drill deep,past the plaster and into the brickwork to get a firm hold, ordinary red wall plugs with no 8 or 10 screws depending on the depth you have to drill,good luck, Terry


Answered 18th Apr 2011


Try drilling the holes deeper and make sure you drive/knock the plugs into the wall deeper than the plaster is,you can tap them in with the screw... that way the plaster won't blow as you tighten the screw and the plug expands... and use longer screws to accommodate the extra depth if you have too. It will also help pull your loose plaster back to the wall...

Screws 90-100mm /3.5" - 4" screws should be long enough, you have to add up the thickness of your rail, add 20mm for plaster and you want around 40mm in the wall to hold heavy books... Brown rawl plugs need a 7mm drill bit... If you're using reds it's a 5.5mm drill bit ...but red plugs won't be big enough really for the size of screw you'll need.

Additional update....Try to get 10 gage screws, and use ordinary brown plugs ... 8 gage screws in masonry tend to snap if they are long.... try and get brown plugs that come in a box, not the ones that come on a folded strip...they're not so reliable and split... I agree with BJD Building and Roofing regards fixing plaster first...but if you're happy to live with it :)

Hope this helps



Answered 20th Apr 2011

I agree with Terry & Hamshire Carpenter.
But if your plaster is as loose as you say, I would get this sorted first.
Have you thought about free standing shelving units, comes in all shapes and sizes.


Answered 18th Apr 2011

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