How to tightly fix a self-tapping screw in loose aerated concrete: many craftsmen and fastener manufacturers are silent about this
"Flimsy" dowels simply fall out of the aerated concrete wall, and powerful anchors pull out a piece of material alive.
Manufacturers do not sleep. They developed special fasteners: metal "brushes" (crocodiles), twisted nylon dowels and other special anchors. But these hardware are much more expensive than classic concrete dowels (especially chemical anchors). Of course you have to make money...
Masters are divided into two categories. Some calmly do their job and do not ask unnecessary questions. Others enter into the ears of customers that special fasteners are needed for aerated concrete. And, of course, branded. Put your percentage in the budget.
I'll tell you what kind of fasteners I use for aerated concrete - it holds tightly.
Why fasteners fly out of aerated concrete
Aerated concrete is a porous material. Under load, it collapses easily. Imagine that we use an ordinary nylon dowel for a gas block, the same as we often use for a concrete wall: 6x30 or 6x40.
Under the dowel sleeve we get a small area of support. If you need to hang a photo frame, this will be enough. But if you hang a kitchen cabinet, which we then fill with heavy dishes, the dowel will push a little porous aerated concrete under it. A void will appear above it. What keeps the dowel in the wall in such a situation? Nothing. He takes off.
The dowel flies out because aerated concrete is crushed under it due to the heavy load and small area of \u200b\u200bsupport. What do hardware manufacturers do? Develop special dowels with a larger area of \u200b\u200bsupport.
Such fasteners really work (I haven’t discussed the price yet), but up to certain limits.
Remember that the gas block is a fragile material. Moreover, the more “warm” block we take, the less its strength. Yes, there are gas blocks with high strength and low thermal conductivity, but they are more expensive, so they are less often used.
With a critical effort (and this is not so much needed), a special dowel for aerated concrete flies out of the wall with a piece of this same wall. I have seen this result more often when using "crocodile dowels". I think this is due to the fact that they create additional tension in the material.
What fasteners still use for gas blocks
I use regular dowels for concrete. They hold up well even in gas blocks. Only instead of short ones, I use long dowels - 100-150 mm.
This approach solves two problems at once:
- Creates less stress on porous concrete. Due to the greater length, the area of support for such dowels is also higher than for short ones. I did not take measurements, but I think that it is comparable to the area of \u200b\u200bsupport for special dowels for aerated concrete.
- Does not break out with a piece of wall. The anchoring point for an ordinary long dowel in the wall is deeper than for a special, but short one. With due perseverance, of course, you can break anything, but you need to make a lot more effort to pull out a long dowel with a wall fragment.
By the way, ordinary long dowels cost, as a rule, less than special fasteners. Draw your own conclusions.
Sometimes masTera use long metal dowels. Screwed out into the gas block without any bushings. This works too.
There is a nuance
All fasteners, which I considered above, are designed for static loads. If you need to fix a horizontal bar or cornice with curtains that you will pull daily, sooner or later the fasteners will loosen and fall out of the wall. Even special dowels for aerated concrete fly out.
Under dynamic loads, the porous gas block at the attachment point is gradually crushed with each application of the load. Over time, the mounting hole turns out to be larger than the dowel itself.
In this case, manufacturers have developed chemical anchors. Have you seen the prices for them?) That is why I usually use improvised means.
I drill a hole, half-fill it with liquid nails, and hammer in the dowel. The adhesive composition fills the voids - reduces the mobility of the dowel in the hole to zero and increases the area of \u200b\u200bsupport. Such fasteners perfectly tolerate even dynamic loads. Compare the price with chemical anchors and draw your own conclusions.
I use conventional dowels 6x100 - 8x120 for the vast majority of tasks where it is necessary to ensure reliable fastening in aerated concrete. Holds tight.
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