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I am planning to do some minor jacking of the main beam of my house (two stories with a lot of furniture and books) and some of the joists in order to correct a sag of about 1/2" and replace old "timbers" (literally tree trunks) with concrete lolly columns. According to books I have covering this kind of renovation, the recommendation is to use a hydraulic jack (like a 40-tonner) to do a micro-lift, then actually hold it with a screw jack (say a 25-tonner). After the screw jack is tight, you remove the hydraulic jack. Then the next month you put the hydraulic jack back again and repeat the process. You only need one hydraulic jack which can be used to service all your screw jacks.

On the other hand I have read accounts of people doing small jacking jobs and they seem to claim that you can actually lift with the turning bar/screw jack directly and seem to have success without the added help of a hydraulic.

Should I get the hydraulic jack or just try manually using the screw jacks alone first?

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The hydraulic jack is an excellent way to be sure you have enough leverage, but more importantly, a high degree of control. Jackscrews are not as good at lifting by rotating the leadscrew due to high friction, which is overcome with a cheater bar so there is not as much feel developed. The jackscrew is excellent for holding a load securely, whereas a hydraulic jack might slide if the actuator is not secure.

If you are worried about cost, you can probably get by with a much smaller jack, like 5 or 10 ton. Harbor Freight has a 20 ton jack for $100. My local tool rental has them for $8 per day.

  • So they bottle jack may leak a little so they might loose some pressure? – milesmeow Apr 16 at 7:09
  • @milesmeow: Best to use a solid block (or stack of them) to hold the weight safely. Use the bottle jack only for moving the load. Then immediately chock the load in place. Best to have a helper or two so that the jack isn't unmanned. That way if anyone gets pinched or caught by slow leaking, the "jack pumper" person can immediately release them. – wallyk Apr 16 at 7:15
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    I see. So don’t leave the jack in place. Use it to lift so that we can remove the old post, for example, and then lower until another temporary post will hold the weight. – milesmeow Apr 16 at 7:57
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I can attest to the other answer(s) here as to the utility of the 20 ton hydraulic bottle jacks for this purpose. I purchased two of them for a very similar project where I was taking out an existing metal support post and sistering an existing beam with three glue lams to gain a clear span support.

The bottle jacks worked extremely well.

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