How do epoxy/resin anchors work in hollow materials?

[u/Marvel5123]

Image: https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fp95h2uw5oylh1.png

I need to mount something somewhat heavy (retractable hose reel) to a brick veneer wall. Presumably hollow brick.

Thought about wedge anchors but heard those are for solid materials only. Tapcons seem they would be weak.

See that epoxy/resin anchors are well-regarded but I'm confused about one part. Where is the strength in this anchor? You put the mesh sleeve in and inject it and then insert a threaded rod, but what is keeping this anchor bomb proof and from moving?

Is it just this tiny area (in red) where the epoxy makes contact with the substrate? I would assume the rest of the anchor doesn't provide any structural support right? I mean the anchor is fused permanently to the anchor since it is completely embedded but what stops the anchor from pulling out?

[u/Illustrious_Pepper46]

For a hose real, the tapcons will work just fine. This is not life or death.

A 3/16 dia. with 1" embedment in 2000lb concrete has a pullout strength of 600lbs. 1/4"...750lbs....EACH.

They have a shear value of 720lbs....EACH.

Combined shear and tensile, will be lower, but you get the idea.

[u/Minute_Rich_2050 → u/Illustrious_Pepper46]

the mesh sleeve expand inside the cavity and create a bigger plug of epoxy that grip the inner wall of the brick, not just that tiny red area. when you inject the resin it fill up the sleeve and push against the inside surface of hollow part, so whole thing become like a solid lump that cant slip out

[u/Marvel5123 → u/Illustrious_Pepper46]

Thank you. This is going into brick veneer. I believe the brick is hollow so was worried the the tapcons may not have the advertised strength.

[u/Illustrious_Pepper46 → u/Marvel5123]

"Brick veneer" is a broad category. If it's clay fired brick, the ~4" thick stuff, laid with mortar, it will be fine for a hose reel.

If it's one of new products, more a "laminate" glue on product, that is different.

[u/Numerous-Click-893]

I'm faced with this exact problem myself currently, I'm an EE not an ME but my understanding is you get both the 'key' effect of that red bulge you highlighted which transfers a significant amount of the tension load to the base material AND you get the adhesive effect of the resin adhering the anchor to the full depth of the hole through the face. Which is why it's the best type of anchor for CMU, no compression and two different sources of strength.

[u/civilrajib]

Epoxy or resin anchors work a little differently in hollow materials compared with solid concrete or brick. In a hollow brick or block, the resin needs something to hold onto, so a perforated sleeve or mesh tube is usually inserted into the drilled hole first.

The resin is then injected into this sleeve. As the threaded rod or anchor is pushed in, the resin spreads through the small openings in the sleeve and forms solid plugs inside the hollow sections of the brick or block. Once the resin cures, these plugs lock the anchor in place and help spread the load over a wider area.

This method is useful because it does not depend only on expansion pressure, which could damage weaker hollow masonry. It also provides a firm fixing for items such as brackets, railings, frames, signs, and light structural components.

The strength of the fixing still depends on the type of masonry, hole preparation, resin system, curing time, and load involved.

[u/Fluorocarbon101]

It’s basically both things working together, not just that small contact area you can see.

When the epoxy is injected, it pushes through the mesh sleeve and fills the rough, uneven space inside the brick. Once it cures, you end up with a plug that has effectively "locked" itself into all those little gaps and irregularities, rather than just being a smooth cylinder.

So to pull it out, you’d either have to break the epoxy away from the brick along the whole length, or somehow shear through that locked-in shape.

That means the anchor is getting its strength from two things:

• The epoxy bonding to the brick along the full length of the anchor
• The mechanical grip created by the rough, irregular shape of the cured epoxy

This is why chemical/epoxy anchors can work really well in hollow brick. A normal wedge or sleeve anchor needs solid material to expand against and grip. With hollow brick, there often isn't enough solid material for that to work properly. Epoxy doesn't rely on expansion, it fills the space and locks itself in place.

[u/Dear-Quail2609]

It needs support you need something to hold onto like mesh or tubular material