The use of conventional construction plywood instead of water-resistant in amateur shipbuilding. Protection of plywood from moisture
If there is no waterproof plywood...
The advantages of waterproof plywood as a material for amateur construction of small vessels are well known. However, as practice has shown, quite satisfactory results can be obtained by using less water-resistant plywood — up to ordinary construction, if certain measures are taken to protect it from delamination. Naturally, it is advisable to use construction plywood only when building small vessels — motorboats, shvertbots, aces, which can easily be pulled ashore for inspection or repair, and most importantly — storage in case of long breaks between exits.
It should be borne in mind that very often the delamination of plywood begins not from the outside, but from the inside of the hull, so in all cases the presence of water in the boat is extremely undesirable. It is better if the boat is equipped with a reliable awning or a light cabin, but it is necessary to ensure natural air circulation indoors. On a boat made of construction plywood, there should be no waterproof bulkheads and buoyancy compartments (foam is used to ensure unsinkability). Slats, seats, stitching should be made latticed so that they do not interfere with air access.
During the construction of the hull, it is necessary to provide a network of scuppers located in such a way that all the water entering the boat flows freely to a certain place from where it could be easily removed. With a completely flat bottom, it is difficult to achieve this, therefore, it is not worth using non-water-resistant plywood on boats with a bottom keel angle of less than 4-5°, in my opinion.
Details such as connecting knits, floras, braces, cockpit linings (coamings), due to the complexity of protecting their edges from water, should be made of waterproof plywood, thin boards or plastic (textolite, getinax). In some cases, thin duralumin is also used.
Plywood intended for cladding boats, must be carefully inspected. Sheets with non-adhesive or insufficient strength of adhesive joints (layers are easily separated from each other with a chisel) are unsuitable. Plywood is often produced, the outer layers of which consist of veneer strips; the outer edge is usually not glued along the edges of these overlapping strips, and it must be carefully cut off with a chisel.
Construction plywood must be impregnated with natural drying oil. This is how it is done. A layer of drying oil is applied, after which the surface of the plywood is ironed, heated to a temperature of 150-200° C. The procedure is repeated until the plywood ceases to absorb drying oil. With such a hot impregnation, the drying oil penetrates deeply, up to the adhesive layer, which becomes somewhat more water-resistant. The inner side of the skin must be impregnated before installation on the set, the outer side — after.
However, impregnation with drying oil and subsequent application of oil paint is not enough. In a year or two, the paint will be covered with a network of microcracks (especially at the heads of nails and screws), through which water will begin to penetrate the plywood. Attempts to get rid of these cracks by applying a new layer of paint will be fruitless, since the resulting thick layers of paint will be very fragile and will crack quickly. The owner of the boat will have to remove all the old paint every year and re-paint the boat.
The strength of the paint layer can be significantly increased if it is reinforced with fabric. The best protection of construction plywood impregnated with drying oil is provided by pasting with thin and rare fiberglass on a 6C or 6T varnish. Good results are obtained when pasting with ordinary gauze on the same varnish. Epoxy and polyester resins should not be used, as they have poor adhesion to the prooliflenny wood. As a substitute, you can use 4C, 4T varnishes or various floor varnishes.
I recommend this sequence of works. A layer of varnish is applied to the drying oil-soaked plywood; after a few hours, when the varnish thickens, a cloth is applied. For a tighter fit, the fabric is tapped with a miter brush, periodically wetting it with turpentine. After several days of drying, the surface is varnished again, then dried, putty with liquid lacquer putty and painted with oil enamels or oil paint diluted on natural drying oil or on a mixture of natural drying oil and varnish 6S.
In addition to pasting on varnish, we can recommend pasting on nitroemal or nitroglyptal paint. In this case, denser grades of matter, such as calico and calico, can be used. When impregnating with drying oil, it is necessary to carefully ensure that there are no smudges, because in such places the nitrous paint falls poorly. The order of pasting is as follows. After drying, the plywood primed with liquid paint is covered with a thick layer of thick nitro paint or solvent-diluted nitrospackle. After a few minutes, a layer of fabric is laid on the plywood, which is tapped with a miter brush wetted in a solvent for nitro paints. After drying, the surface is putty with liquid nitro paint. It should be especially cautioned against the abuse of putty: the thicker its layer, the less durable the coating.
Pasting construction plywood is recommended on both sides; in any case, this condition is mandatory for the bottom. The inner surfaces are glued before installation on the set. Reinforcing the paint with fabric increases the strength of the coating, but, of course, does not make it eternal. Over time (two to three years), the paint layer is covered with a network of small cracks and during repair it will need to be removed with a coarse-grained glass skin, covering the cleaned surface with a new thin layer of paint.
Mandatory edge protection measures and joining of plywood in the manufacture of a housing made of non-water resistant grades
1 — plywood construction; 2 — plastic or water—resistant plywood; 3 — plywood pasting (fabric, gauze); 4 — gasket impregnated with elastic grease; 5 — rivet; 6 — screw; 7 — protective collar (oak, pine); 8 — shackle (steel); 9 — falshkil; 10 — cheek pads; 11 — details of the longitudinal set.
Joining sheets of construction plywood is best done «on the mustache» on waterproof glue, but you can also use a simpler version with a butt strip 100-150 mm wide, cut from waterproof plywood or plastic. The sheets joined on the strip must be previously pasted on the inside; in addition, a strip of fabric or gauze soaked with grease must be laid between the strip and the sheets.
The grease can be prepared from thickly rubbed paint with the addition of 10% antiseptic (creosote or used engine oil) or according to the following recipes: drying oil — 50%, antiseptic — 10%, rosin — the rest; drying oil — 20%, antiseptic — 10%, chalk — the rest. Such lubricants never completely dry out, retain high elasticity and reliably protect the joint from water even with significant vibration of the housing.
The same gaskets with elastic grease should be put on the set before attaching the skin to it.
Before installing nails (screws) into pre-drilled holes with an old syringe, you need to inject a little drying oil, and if the fasteners are not galvanized, lead meerkat.
In the most vulnerable places of the hull (keel, cheekbone, timber), it is necessary to protect the edges of the plywood from damage with collars, linings, false keel, installing them on gaskets and fixing them with a minimum number of screws with a double introduction of drying oil into the holes.
Decorative plywood has significantly greater water resistance than construction. When using such plywood, it is necessary to take into account that neither varnish nor resin fall on the decorative layer, and if it is not protected, then under the influence of water and the sun it will quickly be covered with a network of cracks. Therefore, it is necessary to sheathe the hull by laying plywood with a decorative layer inside, and during operation it is especially important to prevent the accumulation of water inside the boat.
When making a case of bakelized plywood, it is necessary to consider protecting the ends from moisture ingress. The fact is that the backfanner intensively sucks water through the ends and, if special measures are not taken, then in the area of the edges it can rot in two to three years. The ends of the backfans should be impregnated several times with 6C varnish, epoxy or polyester resin, and the joints (including along the cheekbones and keel) should preferably be pasted with fiberglass on resin or varnish. It is not recommended to glue the joints with gauze or calico, since with sharp fluctuations in humidity, such a fabric of the backfanner tears. To improve the adhesion of resin and paints to the backfanner, it is necessary to remove a thin surface layer of very hard varnish from the entire outer surface. It is best to do this by heating the surface with a blowtorch and removing the softened surface layer with a scraper made from an old disc cutter.
In the section «Motorboats, boats, yachts — miscellaneous, reviews, tips»
Share this page in the social. networks or bookmark:
bookmark this page
