Wall plugs into Thermalite blocks

[David.WE.Roberts]

Just hung a couple of identical bike racks on an external wall.

One into brick, the other into Thermalite block used to block up an old doorway.

The fixings are 4 off 5* 50 Turbogold screws into brown Rawlplugs.

I know the screws just go to the end of the plugs because the plugs pulled out of the Thermalite blocks.

So what is the best way to achieve a strong fixing?

I can get M5 rawlbolts but these may split the block.

Inner wall will also be Thermalite so special long screws and pugs may not work, although I do have some frame fixings.

Cheers

Dave R

[Andrew May]

Mount a couple of suitable length vertical battens on the wall then mount the bike racks on the battens. That way the force on the screws in the Rawlplugs will be down rather than out.

[The Natural Philosopher]

fill the holes you have made (after blowing out the dust) with car body filler. Stick a pencil tip in the end before it sets as a guide and drill for the screw when it's almost set

mount the bike rack immediately but leave the final tightening of the screw an hour or so.

next time, use a smaller drill for the plugs.

[Dave Plowman (News)]

Think there are special fixings for blocks - a coarse thread screw which goes direct into the block.

[Tim Watts]

On Friday 04 October 2013 14:49 David.WE.Roberts wrote in uk.d-i-y:

Resin anchors...

[David.WE.Roberts]

I do have some special screws for screwing directly into concrete blocks but I thought they were for the harder type of block.

Unless there are two types.

Cheers

Dave R

[Peter Johnson]

Squirt some no-more-nails or similar down the hole and put the plugs back.

[polygonum]

Coat the plugs with a decent smear of polyurethane glue. Push them in and leave to set. Then put in screw. Best not to use water - you want minimal foaming.

Not as good as some other options such as resin bolt but a major step up from nothing.

[harryagain]

Deep holes and push your plugs well below the surface. That way the surface hole will be smaller than in deeper so preventing them from pulling out.

There are special (expensive) plugs for thermalite.

[Jim K]

Yet moisture is necessary to cure the polyurethane....

Jim K

[polygonum]

Enough in the atmosphere and/or the blocks themselves. Might take longer but for many purposes that is not an issue. Or not much of one. If it were absolutely bone dry then maybe I would think bout using a tiny amount.

[Jim K]

ITYM "it makes f*ck all difference"

Jim K

[meow2222]

Compression type fixings have one weakness: AAC is not the strongest stuff in compression, and is already preloaded by the fixing. A glue (resin) bond can give more strength.

NT

[newshound]

Depending on the exact design, with a bike rack you might have quite a large moment tending to pull the top set of bolts out. I'd think about using say 120 mm multi monti's, drilling the correct size of pilot hole of course. Whatever I used, I would try to make it deep (but probably not frame fasteners)

[sm_jamieson]

The trick (not invented by me) is to put in several plugs or frame fixings at different angles so they cannot pull straight out and the pull-out force makes them work against each other. Also, multi-monti / concrete screws have a very shallow thread and are only for use in hard blocks. They will be useless in aircrete.

Simon.

[newshound]

I agree about concrete screws which are a different animal altogether but, while the multi monti has fairly shallow threads, aircrete has a fine structure and as long as you drill a correct size pilot hole carefully, to provide just enough room for the "core", they will grip. But you do need a reasonably good length: if you let them waggle around they will enlarge the hole and you are stuffed (without using resin as well). After drilling the pilot hole, push a straw right down to the end and blow, to remove loose debris. Like tapping a hole in metal, if you find the torque is going up you need to back out. It is relatively easy to "strip the thread". You could probably improve the strength by squirting in some dilute PVA (although I have never tried that).

ISTR that the MM was developed for restoration work, because it can be put into soft brick within an inch or so of the edge/end.

I *think* I have seen a "self tapper" which was claimed to work in lightweight blocks, but I have never used them.

[David.WE.Roberts]

Thanks for all the responses so far.

It is a shame that space limitations mean I have to fit the bracket just where the soft blocks are.

How about very long butterfly fixings which will expand in the cavity? ;-)

Cheers

Dave R

[Jim K]

how about chop the crap block(s) out and replace with something better to fix into?

Jim K

[The Medway Handyman]

50mm screws aint not long enough, try 75mm & don't use Turbogold, they cut the plug rather than expanding it.! Use Quicksilver! And Rawlplug Uno!

[Tricky Dicky]

Fischer make a wall plug specifically for aerated concrete blocks such as t hermalite. Ordinary wall plugs usually fail because they rotate in the soft concrete as you tighten the screw, the Fisher plugs have 4 vanes on a slow helix you drill a 8 or 10mm hole (can't remember which)and the plug is ham mered into the hole the vanes cut into the block and prevent turning. It's an excellent fixture I hung kitchen cupboards using them and they did not m ove, you could even undo the screw and the plug stayed in place. They are o nly designed to take one specific diam. of screw and really unsuitable for small stuff. The only problem I encountered was if you hit a mortar line th en it could be difficult to insert the plug. I cannot recall the Fischer pa rt number but I have seen them sold in B&Q in an expensive bubble pack of 5 with appropriate screw.

Richard