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Unread 09-11-2004, 10:46 AM   #1
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glass block mortar doesn't bond?

Help!

I'm in the process of building a glass block shower wall. Yesterday, I slowly and carefully set 2 rows of block. When I was done, everything seemed solid and tight (and surprisingly plumb and level too). This morning, I discovered that the mortar didn't bond to the bottom of one of the glass blocks, though it was bonded just fine to the top of the block below it. So, I decided to gently attempt to remove the mortar from the top of that block so I could replace it, and I discovered that the mortar didn't bond to 3 more surfaces.

I'm using U.S.E. Hickson Products brand 'Stone Mason Glass Block Mortar', with Mullia brand 8x8x3 glass block. I followed the manufacturers instructions which said mix approx 1 gal water with 50# of mortar mix, I mixed 5# mortar mix with 12.5 oz water and let it slake for ten minutes. It seemed like the proper consistency, a little dryer than regular mortar yet it did hold together when I spread it. It didn't, however, stick well to the sides of the block so that was a challenge. The block was in sealed cartons, and so I didn't clean the edges cause they didn't seem to need it. I'm using plastic spacers, and expansion strips on the sides.

The mortar underneath the block that came loose is solid and has a perfect impression of the block! I can't understand why it bonded great to some surfaces and not at all to others. Can anyone help me?

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Sup
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Unread 09-11-2004, 11:28 AM   #2
Davestone
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I'm guessing, but run your finger over the edge of a block to see if it has dust,if not i'd say your mud was too dry,and i'd mash it to the block well,i like to spraed it on the row of blocks and also on the individual sides,to avoid voids, and mix it a little wetter,i've found almost every manu. ratio on everything is usually a little dry
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Unread 09-11-2004, 03:48 PM   #3
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Dave,

The edges are "factory fresh and clean" right out of a sealed carton. I'm wondering though why the mortar stuck so well to some edges but not to others. Oddly enough, the verticle edges that I had such a hard time with are sticking the best.

I took the 5# right off the top of the bag, should I have mixed the contents of the bag before I started? Nothing that I read said that was necessary. Everything that I read said that the mixture should be on the dry side because the glass block doesn't absorb the moisture. I guess I'll try a slightly wetter mixture and see what happens.

Anybody got any ideas on how to salvage the work I've done where the blocks are loose on one edge? ... I thought about using silicone caulk to adhere the block to the perfectly formed mortar bed. That feels like a "duct tape" kind of fix but I can't think of any other way of dealing with it.

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Unread 09-11-2004, 04:42 PM   #4
Davestone
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I would use the silicone and put a reinforcement row the next row up.After all silicone is an acceptable method.The reason the sides held is cause you mashed it on harder there.If you're using the spacers you'll be fine with the mortar being a little moister.
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Unread 09-11-2004, 04:52 PM   #5
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Sounds like the same to me. Mud was too dry. If the mortar is mixed properly it should stick like glue. If you don't have too much done you can clean off the ones you started with and start over.
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Unread 09-11-2004, 09:14 PM   #6
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Thanks guys for your advice!

I kinda wanted to see how stuck the mortar was to the block so I took a hammer and chisel and removed it. Where it stuck to the block, it was really stuck! In fact, a row of three tiles are still holding together on the verticle after chipping the mortar off the tops and bottoms. Tomorrow, I start again using a slightly moister mix.

Wish me luck,

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Unread 09-12-2004, 08:43 AM   #7
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I agree the mortar was too dry. It may have been mixed correctly, but you may be working too slowly. Don't lay out the bed joint all the way across. Lay enough mud for one block at a time.

And it doesn't hurt to have the mud a little wetter as long as you are using the plastic glass block spacers to support the blocks.

I would take it out and start over. That's what I had to do on my first glass block job back when I was really "ignert."
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Unread 09-12-2004, 10:06 AM   #8
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I like to use surgical gloves and apply the mortar to 2 sides of the block then mush it to the spacer, feather the squeeze out with your hands, let it set up some and clean as you go. Also you can use a rubber mallet to gently tap the blocks tight. If any of the residue is left on the block, it is a bear to get off. If you don't wear the gloves the mortar will "burn" the skin especialy if you have a cut somewhere.
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Unread 09-12-2004, 03:56 PM   #9
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Maybe I go to too much trouble but I normally keep some white Versabond mixed and apply a skim coat on the block's edges, not alot, you don't want it mashing out, only a skim coat. I have made windows out on a concrete slab and picked them up the next day and set them in place without them falling apart. I've done this a couple times when I couldn't get to the back side to clean the blocks.
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