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How to fill wall/wall gaps before taping a corner

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  1. #1
    Golden Member Gooner's Avatar
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    Default How to fill wall/wall gaps before taping a corner

    I have put up some villaboard walls and need to tape up the wall/wall joints.

    I will be tiling the bottom 2 meters, and so I am simply siliconing the 6mm gap between wall/wall joins in order to provide a bond breaker for the waterproofing membrane.

    However, I will be painting the top 40cm from the ceiling.

    My question is, whats the best way to fill the 6mm gap in this area before taping the joint? I find that the pre-mixed "wet area" base coat I am using tends to shrink too much and doesn't really seem suited to fill the 6mm gap.

    Should I perhaps fill using cornice cement? Silicone?

    Had a look at Rod's "How2Plaster" site. The video on taping corners seems to imply to use base coat, but that doesn;t seem to be working well for me.

  2. #2
    Tool Whore - 1K Club Member Vernonv's Avatar
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    Hi Gooner,
    I had a similar issue when I was doing some joints (I like to seal them up before taping). I simple filled the joint, waited for it to dry (and crack/split) and then filled the crack a second time. I wasn't using premixed stuff (using bagged stuff) and the gaps to start with were about 10mm wide. I've never had an issue using bagged base coat with smaller gaps (like the size you mentioned).

    What brand of base coat are you using?
    Cheers.

    Vernon.
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  3. #3
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    I'm with Vernon here, the pre-mixed base coat may not be as versatile in it's applications, I have had no difficulty filling pretty big spots with bagged base cote and there was no cracking

  4. #4
    Golden Member Gooner's Avatar
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    Thanks for the responses.

    I am using a pre-mixed Gyprock brand "Wet Area base coat". They sell it at Bunnings. Has performed well on the recessed joints. Just not good at filling wide gaps.

    Perhaps I should go an have a look at getting a bag of base coat. Seems a waste to discard the half tub of stuff I already have and buy a bag of base coat to complete such a small job.

    I'm wondering if cornice cement would do for this purpose. I'll have to go over it with base coat anyway.

  5. #5
    Tool Whore - 1K Club Member Vernonv's Avatar
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    Why not just go over the cracks a second time (after the first coat is dry) - that should fill them up.
    Cheers.

    Vernon.
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  6. #6
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    Cornice cement will work fine. For a pre-fill, which I recomend for gaps over 2-3mm prior to taping, make the mix a bit thicker. I also use a lot of salt so the mix sets almost instantly. This allows you to scrape it back straight away before taping. On smaller jobs I use cornice adhesive for taping and 2nd coating then top coat over. Cornice adhesive is made to set quicker when worked, with salt this works even better. Base coat also responds to salt but not as quick or as well as cornice adhesive.

    Not a fan of the wet area base coat for any purpose. Mosy of the testing has been done on wet areas using paper tape and standard base coat. The companies like to bring out more sofisticated products that they make more money from!!!

    Using a premixed product means you have to wait for it to dry before taping and you are right pre-mixed products have a greater rate of shrinkage.

    Cheers Rod

  7. #7
    Golden Member Gooner's Avatar
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    Quote Originally Posted by Vernonv View Post
    Why not just go over the cracks a second time (after the first coat is dry) - that should fill them up.
    The shrinkage with the particular product I am using is actually quite severe. I even have to fill up 3mm nail holes about 3 times before they disappear! I could perservere and keep on filling, but just doesn't seem to be the way to go at this stage.

    Quote Originally Posted by rod@plasterbrok View Post
    Cornice cement will work fine.
    Thats what I wanted to hear. Will give this a try tonight with the salt trick. Once agin Rod, your expert advice is much appreciated on this forum.

  8. #8
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    I'm with Rod as well....I find wet area base coat rubbish. Base coat is still fine with other manufacturers other than csr so that is what I would recommend.
    Honestly I reckon for a shower recess just caulking all joints up with sikaflex would be a better solution as far as waterproofing is concerned. That is what waterproofers do for the junction between the bottom of the sheet and the floor which is a critical joint so I can not see why this couldn't be applied to the recess joints and internal corners as well. The only down side is a tiler might have a winge that the recesses aren't filled correctly but I could only see this being a valid point if you are tiling the shower recess with mosaics.

  9. #9
    Golden Member Gooner's Avatar
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    Quote Originally Posted by Halfie View Post
    Honestly I reckon for a shower recess just caulking all joints up with sikaflex would be a better solution as far as waterproofing is concerned.
    Well I was just about to use a neutral cure silicone for these joints. I thought it would be the "safest" way to go. I could go and replace with sikaflex. Which type of sikaflex? Would this generally be better than silicone?

  10. #10
    Tool Whore - 1K Club Member Vernonv's Avatar
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    Gooner,
    I would use whatever sealing product the waterproofing membrane manufacturer specified ... same goes for how you handle the recessed joints.
    Cheers.

    Vernon.
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  11. #11
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    The waterproofers I know use a product called Chemind Aquaguard.
    Chemind recommends sealing all joints,cracks gaps and internal corners with Chemflex PU (polyurethane).

    http://www.chemind.com.au/datasheets...ard%20Blue.pdf

    Chemflex is their brand of Sikaflex. Bostik and Powers fasteners also make a Sika like product designed for the same applications. Any would do but I wouldn't use silicone as I have never seen it done before.... better to be safe than sorry.

  12. #12
    Golden Member Gooner's Avatar
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    Well at the moment I was looking at using the Ardex WPM001 waterproofing membrane as discussed in another thread where I asked about waterproofing. The data sheet for the Ardex stuff only mentions using neutral cure silicone for all joints and fasteners. No mention of anything else. (...except base coat for recessed joints.)

    In this case, I was wondering if a polyurethane sealant is also a suitable alternative. I believe they do a better job "sealing" but not sure if they are compatible with the waterproofing membrane. May give Ardex tech support a call and ask.

    At the same time, as someone else pointed out, the silicone only really serves as a bond breaker. Therefore, silicone at the wall/wall and wall/floor joints may be the best way to go.

  13. #13
    Tool Whore - 1K Club Member Vernonv's Avatar
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    Hi Gooner,
    The other thing to consider with the recessed joints is that filling them with base coat joins the two sheets together and stiffens the join area (it basically become like 1 sheet, rather than 2). Using a sealant on the area, won't provide the same effect and the movement between the sheets may exceed what the sealant can handle.

    For my money, I would go with what has been used successfully for many years (and what manufacturers recommend). You don't want to "try" something out and find that it fails, especially after your tiles are up.

    Just my $0.02 worth.
    Cheers.

    Vernon.
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  14. #14
    Golden Member Gooner's Avatar
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    Quote Originally Posted by Vernonv View Post
    Hi Gooner,
    The other thing to consider with the recessed joints is that filling them with base coat joins the two sheets together and stiffens the join area (it basically become like 1 sheet, rather than 2). Using a sealant on the area, won't provide the same effect and the movement between the sheets may exceed what the sealant can handle.

    For my money, I would go with what has been used successfully for many years (and what manufacturers recommend). You don't want to "try" something out and find that it fails, especially after your tiles are up.

    Just my $0.02 worth.
    I have already used base coat with paper tape for the recessed joints. No problems there.


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