# Tapcon weight holding capability

I have little experience with concrete screws and don't know their weight-bearing capacity.

Would four (4) 5/16"-diameter ("heavy duty") tapcon anchors, each 3" in length, screwed into the mortar of a brick wall that's in good condition, be able to support a flanged metal rod with equipment hanging on it, the total supported weight being about 100 pounds?

• What is the holding capacity of the mortar? Commented Jan 22, 2022 at 18:24
• I don't know. The wall was built around 1950. Commented Jan 22, 2022 at 18:32
• What kind of brick? And is drilling a couple of them into the brick an option? Commented Jan 22, 2022 at 18:33
• Understood. My best suggestion is to try it in the mortar and carefully load it, then. If you find that it pulls out because the mortar is crummy, then you can move on to the next most invasive option. Commented Jan 22, 2022 at 18:43
• @AloysiusDefenestrate did you mean the least most invasive option? Commented Jan 22, 2022 at 21:36

Although from experience we could conclude that 4 heavy duty Tapcons will hold a 100lb weight whether in brick or its mortar, let's work through the spec and material calculations to see if we were just lucky that it never failed or that we were lucky that we never overloaded.

## Tapcon's specs

According to Tapcon single 1/4in Tapcon can be loaded 250lbs in tension or 620lbs in shear if embedded 1in in lightweight block. Your's is 5/16in so expect even a bit more.

Your rod assembly puts the screws in shear load

The top screws may be under tension too, depending on your rod assembly, if the distance from rod to wall is not much less than the distance from the rod to the top screw.

## Strength of Mortar

Typically, mortar has less compression strength than the bricks it holds, at perhaps 50% to 70%. If we assume brick strength of 5Mpa, then 50% of that is 2.5Mpa for the mortar.

Is 2.5Mpa for the mortar reasonable?

It matches the strength of type "O" mortar. We don't know what mortar was used, but we do know that the numbers we're working with are conservative, based on the weaker mortar.

## Mortar vs Tapcon's "Lightweight Block"

"Lightweight block" is listed by Tapcon to hold 620lbs shear, and it is rated at 3.6Mpa (3.6N/mm^2) compression strength.

Calculating by ratios puts the maximum shear load in mortar (at 2.5Mpa from above) at 2.5/3.6*620lbs = 430 lbs per screw.

## Your 4-screw rod

Your 100lb load will distribute over the 4 screws you plan, plus any friction between bracket and wall. Assuming zero friction as a most conservative estimate, this leaves 25lbs shear force per screw, or a mere 5% of the maximum static load capable.

As for tension (if it applies, see above), the load on the top screws could be around 50lbs each for a 1:1 lever, with the screw rated at 250lbs each.

It seems you have plenty of margin.

## Static or dynamic load?

Your failure mode will not be the screw, but the unknown compression strength of the mortar at the specific but random locality where the screw penetrates it. Relying on several screws, 4 in your case, each singly capable of handling the maximum load, is prudent and provides plenty of margin.

Also note that all calculations are based on static loads. For dynamic loading, e.g. hanging up the equipment, you should include a factor of perhaps 5x. That still keeps you at 25% of the maximum load.

## Brittling over time

Material fatigue is an important further consideration.

Consider that with every dynamic action some of the mortar risks cracking and brittling away due to the sharp screw thread to mortar interface.

The multi screw arrangement will somewhat mitigate this.

Usually shear strength does not require more than say an inch of penetration, but in the case of mortar, the 3in length is an advantage to help overcome fatigue or soft pockets, and so there's a good chance it will remain firm over time.

How the mortar responds to drilling and driving would affect my confidence, and for 100lbs I'd rely on that. For loads of say 1000lbs (well above what I can personally test) I would go by the spec sheet, and mortar isn't covered.

## Nylon plug

If you notice brittling over time, you should consider a screw & plug arrangement rather than the present plugless screw.

A nylon plug will help "soften" the dynamic load transfer from the sharp threads into the brittle mortar and help avoid or delay fatigue of the mortar.

Data & images:

• It all comes down to the unknown compression strength of the substrate. Afaik Tapcons don't have a spec for going into mortar because they're not supposed to (not that I've never put them there; some brick is just too tough). 100 lbs guaranteed. Two 300lbs men doing pull-ups? Probably. I've driven thousands of them; Depends on how it felt going in. Commented Jan 24, 2022 at 14:22
• @Mazura Agree that the drilling and driving affect my confidence, and for 100lbs I'd rely on that. For loads of say 1000lbs (or your 300lbs heavies) I would go by spec, and mortar isn't covered. I also think with a 3in length there's a good chance it will remain firm over time. Commented Jan 24, 2022 at 15:32
• Excuse me, Professor @P2000, how many credit hours is this answer worth? Nicely done! Commented Jan 24, 2022 at 17:14
• @FreeMan So far worth one measly vote (and I think I know from who)... so, as I'm sure you agree, we do it for self-inflicting fun, not the credit hours... ;) Commented Jan 24, 2022 at 18:34
• @mrblint of course, good luck with the project. I made an edit to point out that the top screws may be under tension too, depending on your rod assembly, but in any case, test it and keep an eye on it! Commented Jan 24, 2022 at 20:51

Fundamentally, your approach is sound. Tapcons are designed for brick/stone/mortar. Those particular tapcons are suitably beefy. You have the advantage of pulling mostly down, which is quite strong as compared to pulling straight out.

If you’re lucky, your mortar will be solid and you’ll be able to get the screws into vertical channels. (I’m guessing that the spacing doesn’t allow you to be at the top and bottom of a brick. If it does, do that and you’re ahead of the game.)

The issue that can trip you up is that mortar can be soft and crumbly. I’d try the simplest version first and gently weight the hanger with your intended load. If the mortar fails, then try with one of the screws (preferably the top one) in the brick and the bottom one in mortar. (Technically, I don’t think you are supposed to re-use these, but if all you did was put them into soft mortar, it’s not like it’ll be a big problem.)

If that fails too (unlikely!) then either set 4 anchors in brick, or start searching for studs behind the brick that you can put a long lag screw into.

• Squeaked by on the spacing -- top screw is immediately above a brick and the bottom screw is just below one. The trickiest part was keeping the bit from wandering while starting the hole, since the mortar had a concave curve. Commented Jan 24, 2022 at 22:40