Short answer. Generally a bailee cannot hold onto a borrowed item as security for money the lender owes. However, there is one narrow exception: the bailee has a right of retention for damages caused by the lender's known flaws that were not disclosed before the loan — and that specific exception lets you retain the thing.
What the law says
The bailee cannot retain the thing loaned on the ground that the bailor owes him something, even though it may be by reason of expenses. However, the bailee has a right of retention for damages mentioned in article 1951.
Civil Code, Article 1944 — No Retention Except for Damages. Read the full provision →
The general rule: no retention
Article 1944 starts with a firm prohibition. A bailee cannot hold on to a borrowed thing simply because the lender owes the bailee money — not even money for expenses the bailee incurred while caring for the thing. The right to sue the lender for reimbursement exists, but that right does not translate into a right to keep the borrowed item as informal collateral. This prevents the bailee from using the loan as leverage to pressure the lender into settling unrelated debts.
The exception: retention for Article 1951 damages
Article 1944 carves out one exception by expressly referencing Article 1951. Under that provision, the bailor who, knowing the flaws of the thing loaned, does not advise the bailee of the same, shall be liable to the latter for the damages which he may suffer by reason thereof. If your injury was caused by a defect the lender knew about but concealed from you before handing over the equipment, you fall squarely within this exception. In that situation you may retain possession of the thing until those specific damages are settled.
What you must be able to show
To invoke the retention right, the key facts are: (1) the thing had a flaw; (2) the lender knew about that flaw before or at the time of the loan; (3) the lender failed to warn you; and (4) you suffered actual damages because of that flaw. If the lender did not know about the defect, the liability rule is different — a bailor who was unaware of the flaw is generally not liable for resulting damage. The burden of proving the lender's knowledge will effectively fall on you in a dispute, so document what happened, when you notified the lender, and what you spent or lost.
This is security, not payment
Retention under the exception is a holding right, not a right to sell or keep the thing permanently. You hold the borrowed item as informal security while you and the lender work out or litigate the amount of damages owed. Once those damages are paid or judicially resolved, the right to retain ends and the thing must be returned. Using retention as an excuse to permanently keep the borrowed item would itself expose you to liability. If you are in this situation, it is worth getting legal advice on how to document and formally assert your claim so the retention is on solid ground.