Glue-in Bolts: Blowout Bulb vs Compressed Air

I am curious if anyone has done any testing on the pullout strength of bolts installed in holes cleaned without the use of compressed air. I've always stated that the use of some form of compressed air (I use keyboard cleaner) is required for one simple reason. No matter how many times I brush-blow-bush with a blowout bulb, using compressed air at the end still ends up removing a ton of dust that the blowout bulb did not.

I've spoken to Hilti, Simpson, Powers and a few others and all of them say that compressed air is mandatory. They all said a blowout bulb is not sufficient which matches what I've seen.

Does anyone have any testing data or other experiences on the matter?

No data. Sorry.

In my canyoneering bolting kit rather than a blow bulb I have about 18 inches of surgical tubing, and then my lungs serve as the source of air. Between that and brushing I seem to get a pretty clean hole.

I thought it was recommended by many and pretty standard to use one of these. They work far better than any other blow tube or bulb I've used.

climbtechgear.com/powers-ha…

But, I often use a portable 10 gallon air tank that I connect a 50 or 100 foot hose to. It cleans out holes like a dream, as well as the route as a whole, and doesn't involve throwing away cans of compressed air.

I've seen data somewhere that involved the weakness of glue-ins from holes that aren't cleaned out at all (around 90% weaker). But, not specific to compressed air versus other means of cleaning out the hole.

JK- wrote:I have about 18 inches of surgical tubing, and then my lungs serve as the source of air. Between that and brushing I seem to get a pretty clean hole.

I've tried that and unfortunately it doesent come anywhere close to cleaning the hole as well as compressed air. Your lungs can only produce around 3 PSI if you try your hardest. Powers and Simpson recommend a minimum of 70 PSI.

I inspect this stuff for a living on commercial projects. The pump blowers work just fine. Fortunately in dealing with holes big enough to get a finger into to check. If white doesn't come out on my finger, It's clean. I have constant issues with unacceptable cleanliness on glue in anchors.

Does anyone have experience with the refillable canned air alternatives like this? canlessair.com
I have used the throw away bottles for cleaning routes, but have always wanted an alternative that was a little greener. I don't know how long these things last or how much pressure you get. They seem to cost around 100 bucks and I wanted to know if it was worth it. Sorry to highjack the thread a little.

Bolt Products Testing

Top
Hole blown out with blower.
Pull-out 1060kg/10,4kN

Centre
Hole blown out with compressed air at 8 bar.
Pull-out 1560kg/15,3kN

Bottom
Hole blown, brushed and blown with blower.
Pull-out 3540kg/34,7kN

As you can see the better the cleaning of the hole the better is the adhesion to the test block and less glue remains on the bolt. (The glue tends to crumble under high load and falls off when extracted.)

No test data to support this, but...

I've always thought the mechanical brushing action of cleaning the hole was as important as blowing out the dust. Brush, bulb, brush, bulb, until hole is "clean".

Always thought that using a blow tube introduced way too much moist air into a dry hole. Maybe not a concern for some glue ins, but...

Have used compressed air. Nice! But, a pain to have to lug that extra stuff around.

I've always used a blowout tube, brush/blow until absolutely no more dust is coming out. Have done some testing with a Dynamometer that seems to indicate that this method is plenty sufficient.

John, in our sandstone at RRG, it is generally hard enough that excessive brushing is not a concern. Of course as with any glue-in we use nylon brushes not wire. Is your stone so soft you just keep creating more dust?

I use keyboard cleaner, too. Figured I was the only one.

I actually use a blow tube, as well, during drilling to remove built up powder. But for the final stage I always hit with compressed air and am surprised at how well it removes that last, ultra thin layer of dust. Just the visual inspection alone is pretty convincing at that stage--almost like you can finally see into every little pore.

Brian in SLC wrote:No test data to support this, but... I've always thought the mechanical brushing action of cleaning the hole was as important as blowing out the dust. Brush, bulb, brush, bulb, until hole is "clean". Always thought that using a blow tube introduced way too much moist air into a dry hole. Maybe not a concern for some glue ins, but... Have used compressed air. Nice! But, a pain to have to lug that extra stuff around.

I'm with you on that but really carrying a small tank of compressed air isnt that huge of a deal for a "close to the road" kind of crag. Even Sears sells one small enough to fit into a pack and blow out 20-40 holes.

IMO improperly cleaned glue ins are just as dangerous as over tightened bolts.

s.price wrote:I use multi edge trimmer line attached to an old drill bit with tape instead of a brush. 4 pieces 8 inches long with 2 inches attached to the drill bit clean a hole a lot better than a brush and does not pack dust down in the hole as a brush will. Blow, weed whack, blow. I use a bulb. Works great.

I like the idea, have you ever run a brush after this just to see how much dust is still there? I've blown holes with compressed air completely clean only to run a brush through and see more dust come out.

James T wrote: Bolt Products Testing Top Hole blown out with blower. Pull-out 1060kg/10,4kN Centre Hole blown out with compressed air at 8 bar. Pull-out 1560kg/15,3kN Bottom Hole blown, brushed and blown with blower. Pull-out 3540kg/34,7kN As you can see the better the cleaning of the hole the better is the adhesion to the test block and less glue remains on the bolt. (The glue tends to crumble under high load and falls off when extracted.)

As you can see the brushing is more important than blowing and both are better than either alone.
I routinely use compressed air when I´m testing in the workshop since it´s right there and always a pump when I´m outdoors somewhere whichever way so long a you brush and blow the results are the same. Even at 9bar the air doesn´t dislodge all the particles in the hole which brushing does.
Blowing with a tube is common but not very effective, not as good as a pump but better than nothing.
Many people recommend a bristle brush because this is what is used in brickwork but we use and sell steel brushes as they are far more effective in rock.
Most important of all is probably rotating the bolt as you insert it to mix any dust into the resin.
If the rock is damp they are hard to clean since it isn´t "dust" any more. best is to wash out with water a few times and use a wet-hole compatible resin OR half fill with glue and use a thin rod (or the drill bit if you´ve nothing else) and rub the resin into the sides of the hole. I just insert some resin and rund the drill in and out a few times, a bit messy but probably the most effective way.

I´m not convinced Hilti, Powers etc think compressed air is "mandatory" as 20kN claims, all sell a pump for this purpose and show it in their instructions (except for diamond cored holes). It is anyway irrelevant for certified bolts as the method of installation is determined by the bolt manufacturer NOT the resin manufacturer as this is how they were certified.

If you want the compressed air effect without using disposable cans, a refillable sprayer works well. Mine can be charged up to 200psi. Not sure how many holes you could blow out on a fill but I suspect a lot.