Soaking Forms In Oil

After the various parts have been cut to proper shape and dimensions, each should be treated with crude oil or a mixture of equal parts of linseed oil and kerosene, so that the lumber will be thoroughly saturated and hence will repel water. This can be done by making a shallow galvanized iron box or tray sufficiently large to receive the longest pieces or parts that will ever be used and allowing these pieces to lie in the oil until they will absorb no more. Then when used, if the form surfaces next to the concrete are wiped with a piece of oily waste and thoroughly cleaned each time after use, it will be found that the forms will not undergo changes in shape that will make them bind when putting together or taking apart. In this way wood forms will also be made more durable. They will serve for repeated use where otherwise their usefulness would end after being filled a few times only.

Another method of treating forms to prevent concrete from sticking to them and to prolong their usefulness is to apply several coats of hot paraffin by painting on with a brush. This method of treatment, however, is more expensive than soaking in crude oil and is no more effective.

Cleaning Forms After Use

Each time after use, forms should be carefully cleaned. Some particles of concrete are quite likely to adhere to the surface and unless this is removed and the surface carefully wiped with a rag or piece of cotton waste soaked with crude oil or the kerosene-linseed oil mixture mentioned, form removal will be difficult and imperfections will appear on the surface of the concrete product.

Forms Must Be Tight

Forms must be strong enough to fiold the weight of the concrete without bulging out of shape and must be clamped or otherwise secured together when in use, to withstand tendency to bulge while the concrete is being rammed or packed in the molds.

Design for reinforced concrete panel fence. Posts and panels are cast separately, then assembled as shown. This sketch also shows in detail the forms required for building the posts.

Dressed lumber is necessary where smooth surface finish is desired. Joints must be tight to prevent water from carrying cement from the forms and thus robbing the concrete of its most desirable ingredient. Where boards are used for sheathing on studs such as on a form for a foundation wall, the sheathing boards should be uniform in thickness to prevent unevenness or irregularities on the concrete surface. Posts and studs used for supporting or bracing forms for building walls must also be stiff and strong enough to hold the forms in true line and to prevent sagging when the load of concrete is placed.