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  1. #1
    Join Date
    Mar 2012
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    Default Thin hairline cracks in Plaster Paris - how to fix?

    I am just learning how to be a handy-person. I have patched the nail holes in the plaster using some CGC compound, sanding and then reapplying (for far 5 times). I know it is overkill, but again I am just learning.
    I have noticed some hairline cracks in both the ceiling and the walls. How should I go about fixing this? Do I need to buy that mesh stuff? Any help is appreciated.

  2. #2
    Join Date
    Jul 2010
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    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    Hairline cracks can be fixed without that "mesh stuff".

    You will need to enlarge the cracks just a little bit, using a utility knife, so that the plaster of paris mix that you will prepare for that will go in the wider cracks. You can apply the mix with a brush or with your fingers (it's a lot of fun, but wear thin gloves). Let dry, then sand lightly. IMHO, some very thin and barely visible cracks are not worth messing with.

  3. #3
    Join Date
    Mar 2012
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    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    thank you so much for the reply!
    I have the pre-mixed Plaster paris, so I hope that is ok. And I bought the TAPE rather than the mesh - the store associate talked me into it, so I also hope that isn't a problem.

    UPDATE:
    Well I tried the tape - and not being a professional, it shows way too much. I stripped the tape off and I am just going to use filler in the cracks for now until I know more.
    Last edited by netrate; 03-15-2012 at 12:17 PM.

  4. #4
    Join Date
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    Northern Virginia
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    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    The problems that accrue to using patching plaster by far outweigh the very slight speed advantage/ 1) no chemical bond to the underlying lime plaster browncoat, or the lime & gauging whitecoat. It will hold only by a mechanical bond.
    2) No tensile strength.

    So I recommend either patching with lime & gauging, over mesh tape (for tensile strength), and prime the cracks with a bonding agent (Link or Plasterweld); Or use setting-type mud (Durabond 90) and again, spray, roll or sponge a bonding agent into the cracks to seal and prep the repair so you get a decent shot at a strong bond. Once you gat a coat of Durabond on the repair, you can finis skimming with regular green-lid drywall mud, or trowel on some Easysand 45 (like Durabond only a bit more sandable) to feather it out. In a wet area, (bathrooms) stick with Lime & Gauging or Durabond, they are more forgiving of moisture.
    Casey
    Remove not the ancient landmark, which your fathers have set.

  5. #5
    Join Date
    Jun 2009
    Posts
    271

    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    I would agree with Sombreuil to use a Lime / Gauging mix.
    Plaster of Paris would set very fast and be to hard also could set with very little bond to the existing plaster.
    A good mixture would be about 7 parts Lime & 1 part guaging.
    And if you want it to set faster add about 1/2 part Moulding Plaster ( Plaster of Paris ),

  6. #6
    Join Date
    Mar 2012
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    13

    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    Thank you for the reply. Again, being new at this, I am sure that I am making more mistake than are necessary.
    I didn't read this until today and I had already patched the cracks using CGC compound. I know that this is not Link or Plasterweld, so at least it is only one room that I will have the issue in the future. A question though, will the plaster shift from the seasons? Since I patched it, it is good for a while, or will the cracks just show again in the future and I will have to use the Plasterweld or Link?
    Would this work:
    http://www.canadiantire.ca/AST/brows....jsp?locale=en
    Last edited by netrate; 03-18-2012 at 05:01 PM.

  7. #7
    Join Date
    Mar 2012
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    13

    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    Well, I am disappointed in myself. I patched the ceiling using CGC patch, sanded it about 5 times over 5 days. Did everything I thought was right - and then painted. Well, the paint soaked right into the CGC and now leaves a dark mark over it. I was sure that is was paintable and it would blend. Guess not.
    I am new at this and I really wanted to get it right, but I have a lot to learn. Too bad. Can anyone tell me where I went wrong?
    Here is the stuff I am using on the plaster walls :

    http://www.canadiantire.ca/AST/brows....jsp?locale=en

    I was told this was fine, but I guess not.

  8. #8
    Join Date
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    Northern Virginia
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    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    Did you prime the patch? Was the patch fully dry?
    Casey
    Remove not the ancient landmark, which your fathers have set.

  9. #9
    Join Date
    Mar 2012
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    13

    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    I had sanded it the night before, so it had 24 hours to dry. I did go over it with a damp cloth the night before as well to get rid of the dust, but that is about it. Not sure why it isn't working out.

  10. #10
    Join Date
    Aug 2007
    Location
    The Great White North
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    4,045

    Default Re: Thin hairline cracks in Plaster Paris - how to fix?

    Sounds as though you didn't apply a sealer/primer before painting the patch.
    The sealer/primer does just that --- seals the new material so the paint doesn't just get absorbed into the patch compound.

    As far as longevity to the repair of the crack --- that will depend if it was caused by structural movement. If so then the better choice will be to use the mesh tape and Durabond or Sheetrock 90. These are far harder than the general purpose mix you presently are using. The thing about Durabond and Sheetrock 90 is they set up in about 90 minutes and dry hard --- you have to work fairly quick and cleanly since there is no sanding those materials.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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