Arch Mortar Joint Question

[rodeair]

I've completed my inner arch and am a little worried about the thickness of the mortar joint. I am a novice at this and would appreciate if anyone could tell me if it's OK. I am using 3:1:1:1 homebrew with fine sand. The thickest joint is 3/4" at the top. Thanks

Leigh

[splatgirl]

Re: Arch Mortar Joint Question

I'm not crazy about the look of that, myself. Do you see how you've got some bricks that are a rectangle instead of a trapezoid? Lets assume, worst case, the mortar fails or deteriorates. The premise of an arch is that it is self supporting, and if all of your arch bricks were trapezoids, it would be. Without mortar, there'd be nothing holding those rectangles you've got.
On the bright side, if you want to correct it, you're existing arch gives you a good template for cutting new trapezoid shaped bricks--just add a few degrees of angle on a few of those bricks and you're there.

[rodeair]

Re: Arch Mortar Joint Question

Thanks for the quick reply. I do see your point about using wedges to form the arch. Do you think if I replaced the 5 pieces at the top it would suffice?

[splatgirl]

Re: Arch Mortar Joint Question

I think that to be truly functional, I would replace the seven that are visible. The third brick out from the center on either side are still rectangular and thus ineffective. Think of the proper shape of each brick as including half the existing mortar joint as indicated in red on the photo.
Your center brick is well shaped and could be reused if you can get the mortar off of it.
As I said, I would use what you've got as a reference for how much angle to add to each brick if you redo.

[splatgirl]

Re: Arch Mortar Joint Question

Here's a bit better mock up

[rodeair]

Re: Arch Mortar Joint Question

Everything you point out is understandable. I will redo the arch to be functional on it's own. I can't afford a failure of the dome or arches since this WFO will be completely enclosed when finished. Thanks very much for your help.

Leigh

[rodeair]

Re: Arch Mortar Joint Question

Actually those outer bricks are cut full bricks which were quite a pain. That was part of my reluctance. Does this theory hold for the dome as well? Are you a fan of multiple cut dome bricks, or the number of courses and smaller mortar joints make it stable moreso than an arch?

[brickie in oz]

Re: Arch Mortar Joint Question

If it was me Id leave it, the bottom of arch bricks are close together, thats the critical part not the top.
As long as the arch is buttressed properly with side thrust it shouldnt be a problem with arch failure.

[RTflorida]

Re: Arch Mortar Joint Question

Your dome bricks when properly installed are locked in 2 directions. Your last brick in each course should require and gentle nudge or tap to set it in place, thus locking in that course. When you reach the top of your dome the final plug or plugs should also require a small amount of effort to tap into place, wedging the entire dome in place.
Centuries have proven that precision cuts are not necessary for a dome to remain structurally sound. Half bricks work just fine if you use a wedge for the final on each course and at the last brick in the top.

RT

[rodeair]

Re: Arch Mortar Joint Question

Thanks for the input, I appreciate it. I know the issue becomes "if the mortar fails". In the end, I'm not really crazy about the workmanship of the arch. I'll probably replace the center 5 bricks with 6 wedges and hope the mortar gods are with me down the road. RT, luckily I have been working the dome courses as you explained, although from the next course up, I'll bevel as well as taper for a cleaner joint. Thanks again, you guys rock.

Leigh

[Tscarborough]

Re: Arch Mortar Joint Question

I am with Brickie. You have the inner edges touching, so the mortar is essentially just chinking material. Unless it is physically disturbed, it ain't going anywhere.

[rodeair]

Re: Arch Mortar Joint Question

Well, after consideration, I thought I would use a concrete drill bit to clear the wide mortar joints from the top enough to put a wedge of brick in the center third or so. Found out the ole homebrew is some tough stuff. I'm not proud of the final product, but I'm going to leave it alone and do a better job for the outer arch. I appreciate all of the input. I have read alot of posts from all of you guys. Tscar has taught me alot about cement, mortar, etc.

Leigh

[ajejeje]

Re: Arch Mortar Joint Question

Arch Mortar is very helpful and easy to use.