Fastening to plaster

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  #1  
Old 09-20-06, 01:50 PM
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Fastening to plaster

I have an older brick bungalow, the exterior walls are brick. The interior walls opposite the exterior are not lathe and plaster but plaster on brick. There may be different kinds of plaster or maybe it's morar inside but it's crumbles easily.

I am trying to attach 1/4 inch pine plywood to the back of a bookshelf case on one of these walls. There is a layer of thin foam board between for insulation. I was using screws with plastic plugs. I thought the screws were long enough but I am having a problem with them not gripping in the plaster.mortar.
The plywood is warped and rigid and pulls away from the wall at the corners, and the foam board acts like a spring. The plastic anchors never seem to find the holes I have drilled after going through the foamboard, and just smash when I try to put them in with a hammer.

Is there a better way to attach this? Am I using the right fastener but just need longer screws? They are 1 1/4 inch and the foam and plywood are probably no more than 1/2 to 5/8 inch.
 
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Old 09-20-06, 04:36 PM
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Try longer screws with really coarse threads. Spin them in slowly. You might get some grab in the plaster and brick if they are coarse enough threads.
 
  #3  
Old 09-20-06, 07:04 PM
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Kotka,

Plastic anchors will not work in plaster if there is any weight to what you are fastening.
Also, if you are supporting a bit of weight the plywood backing may also not be suitable for anchoring.

Are these anchors supporting the weight of the whole bookshelf and its contents?
 
  #4  
Old 09-21-06, 01:23 PM
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The plaster over the brick is probably about 1/2" thick - combined with your plywood and foam, that means you are barely touching the brick. The plaster most likely won't stay together even if you did line up the plastic anchors. You need to get into the brick itself. I'd try an inch longer screw - which also means a longer anchor.

I'm not sure what to tell you about not being able to align the holes in the foam with the holes in the wall - I assume you drilled through the plywood and foam to drill the hole in the wall - if nothing moved, they should still line up. Once you have one drilled (deeper like above), put the screw in it, so your can use it to keep the plywood from moving while you drill the others.
 
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