Which resin anchor should I use (old crumbly brick)

[Oldman]

I am trying to set up an air conditioning split system at home ready for a local engineer to come pipe it and commission.
The external fan and compressor unit is being mounted in unistrut on the back wall of the house above a single story extension.
The house is 1963 build & rendered.
When drilling 10mm holes, the render is very hard but the brick behind is very soft and powders easily, I have carefully with pilot holes drilled several 10mm holes and fitted blue wall plugs with stainless M8 coach screws & although they nip up tight, i'm not over confident of the long term holding power of 6 coach screws holding 52kg of Compressor and a few kilo of unistrut in place.
I have never used resin before but reading they seem to state you must remove all loose dust etc from the holes, if I do that I will have no wall left
So real world advice please.

 

[Terry - Somerset]

Most of the stress on the screws will be in shear as the 50+kg tries to fall vertically. If the screws nip up tight I think there is little risk of failure.

Note screws are tight as the screw and plug effectively compress the surrounding brickwork.

Some (much less than vertical) stress will be trying to drag the screws out of the brickwork as the centre of gravity of the unit will be (approx) 250mm from the wall.

If there are vertical channels to which the "shelf" supports are attached, keeping the top channel fixing as high above the shelf as possible minimises the stress on the top fixing as the load imposed by the shelf has to pivot around the bottom fixing.

 

[Oldman]

Thanks Terry, yes 600mm shelf with 300mm wall side empty, I did put 1 screw bottom and 2 near the top as yes its trying to pivot.
Its just the thought of that mass trying its best to set up a vibration in the brick.
Generally I mount stuff that I would happily hang off without fear of crashing & I'm a lot more than 50kilo, I just didn't feel it with this job.

 

[Jones]

It's best to clear the dust from the hole with a blower which has a straw that is pushed to the back of the hole and then pump to blow the dust out. If you don't have a proper one you should be able to make something with a bike pump or a pump for inflatables. It's easy to see when no more dust comes out then you're ready for resin, part fill the hole from the back and insert the fixing whilst twisting it. You may need to wedge the fixing central tothe hole.

 

[rogxwhit]

Good responses above. The main loading is static, after all. And vibrational loadings that might disrupt a friable substrate should be very low from the unit itself.

 

[Oldman]

I had suggested to me that I use These sleeves but M8 ones I needed were not available local to me. although as I dont know if I was drilling into yellow soft brick or mortar and where the frog was they did seem like a very good idea, but hey I can try that next time. I did want to got the job done and I had some old fashioned rawlbolts. Job done. Many thanks for the replies.

 

[jonw1664]

I had suggested to me that I use These sleeves but M8 ones I needed were not available local to me. although as I dont know if I was drilling into yellow soft brick or mortar and where the frog was they did seem like a very good idea, but hey I can try that next time. I did want to got the job done and I had some old fashioned rawlbolts. Job done. Many thanks for the replies. View attachment 140246

Those sleeves look interesting- is the idea that they partially hold the resin? I can’t find any on the internet - is there a special name for them?

 

[Daniel2]

In French they're called "Tamis", but I realise that that's not much help.

 

[Doug71]

Those sleeves look interesting- is the idea that they partially hold the resin? I can’t find any on the internet - is there a special name for them?

Think just resin sleeves.

https://www.screwfix.com/search?search=resin+sleeve

 

[johna.clements]

I had suggested to me that I use These sleeves but M8 ones I needed were not available local to me. although as I dont know if I was drilling into yellow soft brick or mortar and where the frog was they did seem like a very good idea, but hey I can try that next time. I did want to got the job done and I had some old fashioned rawlbolts. Job done. Many thanks for the replies. View attachment 140246

Those sleeves are for hollow bricks and blocks. Where your drill hole passes through the voids inside the wall the sleeve stops the resin escaping into the void so there will be resin available to connect to the brick/ block between the voids.

The fixing manufacturer technical literature will give give the shear and tensile loads that their fixings will take in various materials.

 

[Jones]

Rawl do a very good catalog with all the information you will ever need, it's probably online now. The sleeves are either plastic as in the post above or stainless mesh. They retain the resin around the anchor in hollow blocks and europrean type clay blocks, they're not normally used with UK type bricks.

 

[nickds1]

I am trying to set up an air conditioning split system at home ready for a local engineer to come pipe it and commission.
The external fan and compressor unit is being mounted in unistrut on the back wall of the house above a single story extension.
The house is 1963 build & rendered.
When drilling 10mm holes, the render is very hard but the brick behind is very soft and powders easily, I have carefully with pilot holes drilled several 10mm holes and fitted blue wall plugs with stainless M8 coach screws & although they nip up tight, i'm not over confident of the long term holding power of 6 coach screws holding 52kg of Compressor and a few kilo of unistrut in place.
I have never used resin before but reading they seem to state you must remove all loose dust etc from the holes, if I do that I will have no wall left
So real world advice please.

I've always used Fischer chemical fixings - recently used some to hold a C-section steel joist against a very wet Victorian cellar wall.

If using resin fixings in a wet &/or crumbly wall, you must torque the bolts correctly. If over-tightened they'll just break up the brick more and weaken the fixing. Fischer have tables for torque settings for different conditions.

 

[johna.clements]

Also if using resin in a damp material you have to check that the resin can be used in the damp. Some resins can be used under water others do not like it damp. Some will be ok in a damp wall but you knock off say 20% off the tensile strength.