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Can I place cement board over existing drywall in preparation for a natural stone (quite heavy)installation in my living room? If it's possible, is it okay for the cement board screws to pass over drywall before it reaches the stud as a result?


Here's the project that we completed last month. thanks to Iggy and D moore

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    Please be as detailed & specific as you can be. Cement Board is not the concern here. Can you give us a diagram or a picture of what you might be duplicating? Is this Stone Veneer or locally collected Stone? What's the total weight of the stone? Have your building's structural components been evaluated? What are the dimensions of the project? How far will the stones project out from the wall? Will you have a mantel or hearth? Is the wall interior or exterior? etc. – Iggy Feb 29 '16 at 6:35
  • It's natural stone over 12in. wide glued together out of small rectangular pieces & staggered on the sides approximately 6in. in height & about 6.25 lbs each & thickness vary from half inch to an inch as it's really rough front & back. I'm installing it on my 9 ft by 12.5 ft. wall. It's really heavy. There are no instructions in the box when I got it from Lowe's. I was hoping not to remove the drywall by placing cement board over prior to install but the guy from Lowe's thinks its best to knock the drywall off first not mention the cement bd.screws available are not long enough. – DIY fanatic Mar 2 '16 at 4:55
  • Cement board's best, no paper face. But, DMoore's mesh will do, put 3/4" washers under screws to prevent the mesh from pulling over the screws. If an Emser product the 750 to 800lbs total finished project weight, according to Emser, an Epoxy Thinset Mortar Adhesive is needed - see page 2 - pdf.lowes.com/warrantyguides/759147840733_warranty.pdf Also get a Masonry Sealer - see bottom - pdf.lowes.com/useandcareguides/759147840733_use.pdf Squirt Epoxy Grout between tiles with corner nipped off Zip-Lock bag. Bonus Info emser.com/documenti/setting_materials_pk.pdf – Iggy Mar 2 '16 at 13:01
  • thank you iggy an dmoore. finished it last month used 2.25 inch screws and used cement board as well to reinfoce . very strong thinset used for the mortar. thanks for the input. – DIY fanatic Jun 16 '16 at 19:33
  • Fabulous & so much better, great job!!! Personally, if you're thinking of caulking or mortaring the top & sides, don't...I prefer the black shadow line look & future painting is much easier & cleaner. – Iggy Jun 16 '16 at 23:51
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Given that this if for inside application the first thing I would state is to follow the manufacture's instructions. Depending on the stone weight you will have different install methods.

However... given no info from manufacturer:

  • I would not cement board over drywall. You would have to use longer screw of course but the fact that the screw isn't binding for the first half inch will put some serious strain on this connection. If you are dead set on doing it, glue it then screw it.

  • I would have have personally installed on drywall in dry areas. As long as this isn't a shower I don't see a performance difference between the drywall or concrete board unless the stone was extremely heavy

  • To prep for drywall install I would double up on the drywall screws, install wire mesh over the area, and then give it a small scratch coat over the mesh.

If you can give me specs on the stone I can get more specific or change my answer but nothing wrong with drywall as long as the area isn't wet (and given it isn't on a fireplace but then you shouldn't have drywall there already.)

The math:

Sheet of drywall is 48x96" or 4608 sq/in. The stones are each 108 sq/in. Meaning you will need 43 stones per sheet. The OP says the stones are 6.25 pounds, meaning the wall would be supporting about 260 lbs/sheet.

Each drywall screw can hold about 90 lbs of shear force without tearing drywall. An average sheet of drywall has 30-40 screws. Let's say 30 to give minimalist numbers. That means your sheet of drywall can probably hold 2700 lbs which is 10 times your stone weight.

My focus would be on reinforcing drywall and providing a good substrate - wire mesh. Adding concrete board to me only weakens the connection to the framing - basically you are saying that drywall can't handle the stone but it can handle the backerboard and stone. If you want concrete board then it should be on the wall - I would not use plywood as it does not bond to thinset as good as drywall or backer.

From a practical point of view... I have installed stone more than a few times on drywall. Your worries about the wall falling over are ludicrous. The weight isn't being pulled out. The weight is going straight down. 90% of the installation issues will be with the thinset and its bond. You are focusing on something that has little bearing on your finished product.

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  • I think it makes sense gluing it to support the screws since the screws available are not long enough. The stones are small rectangular pieces glued together making it over about 1.5 ft in length by 6 inches and staggered on both sides. Iit's approximately 6.25 lbs each. Thickness vary from an inch to half an inch and front and back has a rough surface. Installation is on my 9 ft 12.5 ft wall. I'm afraid installing it directly on my drywall take the whole drywall down and probably my life or any of my family members. Thanks for the input – DIY fanatic Mar 2 '16 at 5:12

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