Restoration of Flight Sergeant Heikki Marklund's grave memorial

Suomeksi

The propeller blade from the Martinsyde F.4 Buzzard (MA-34) aircraft that crashed has served for 92 years as the grave memorial of Heikki Marklund, buried in Tyrväntö Cemetery in 1934. The grave memorial restoration was completed in early June. The history of the propeller-blade memorial has been described in an earlier blog post.

The restoration of the badly deteriorated propeller blade began with the use of BioComb HOME, a bio-based mould remover. Before this, the bronze memorial plaque attached to the propeller blade was removed. The surfaces of the propeller blade were rubbed with cloths soaked in the mould-removal liquid. The substance both cleaned the wooden surfaces of the propeller blade and removed mould and organic growth from them. As a result of the treatment it became clear, as we had assumed, that the propeller had once had a varnished surface. The rotten root end of the propeller blade was completely immersed in the mould-treatment substance, allowing the liquid to be effectively absorbed into the blade root by capillary action.

After the anti-mould treatment, we proceeded to impregnate the wood material of the blade. A mixture of Valtti Primer and clear Isotrol varnish was brushed onto the surface of the propeller blade. Isotrol varnish is a linseed-oil alkyd primer. For the solution treatment, a basin was made on the table from strips of wood and plastic film, in which the propeller blade lay half immersed in the solution while the solution was brushed onto its surface.

During the solution treatment, air bubbles began to emerge from inside the wood. This indicated that the Valtti–Isotrol mixture was penetrating into the wood material. In this process, Valtti Primer carries the Isotrol varnish into the wood, displacing air and water from the wood and filling its cellular structure with varnish. At first, 10% varnish was added to the Valtti Primer. With each brushing, the amount of varnish was gradually increased to 50%. After numerous brushings, the wooden propeller blade no longer absorbed the mixture of Valtti Primer and varnish, so the blade had been successfully impregnated.

At this stage, the wooden element on the propeller blade’s trailing edge that had come loose was glued back in place. The original blank for the propeller blade had been made from four pieces of wood glued together. The propeller blank was then worked into the shape of the propeller profile.

The glue joints between the wooden elements of the propeller blade had eroded and partly worn into gaps. The gaps were filled with black Casco Multitech sealant. The sealing effectively protects the gaps between the elements from water penetrating into the propeller.

We considered how to treat the root end of the propeller blade, particularly whether we should saw the ragged root end even. However, we decided not to shorten the propeller by sawing it, but instead to fill the ragged root section of the blade with wood filler. This prevents moisture and ants from entering the propeller blade through its root end. The restoration treatment of the propeller blade was thus complete, and it was time to build the stand.

A completely new stand was built to replace the original rotten one. It was built to match the shape of the decayed stand, but this time it was made from pressure-treated wood. For the lowest part of the stand, we chose 75 x 75 mm pressure-treated timber. From this, two pieces were cut, measuring the length of the frame, 28,5 cm.

The four 28,5 cm parts of the stand, to be attached on top of the lowest wooden pieces, were sawn from 50 x 100 mm pressure-treated wood. These four pieces were joined into a single unit with an opening in the centre, shaped according to the cross-sectional profile of the propeller blade, into which the blade is inserted and fastened.

Although we were making the wooden stand for the propeller blade from pressure-treated wood, we further increased the durability of the wood by treating the stand’s wooden parts several times with grey Valtti Color wood preservative, especially the cut surfaces of the stand parts. This was because the cut surfaces clearly showed that the pressure-treatment agent had not penetrated deeply into the wood. Therefore, in addition to brushing the surface, the wooden parts were placed upright in a plastic bowl containing grey Valtti Color preservative. In this way, the preservative was able to penetrate deeper into the wood from the ends of the pieces.

To make the opening in the stand according to the cross-sectional profile of the propeller blade, we made a template from thin plywood, matching the blade’s profile. The oval opening made in the plywood was fitted to the propeller blade several times by sliding the plywood template from the root of the propeller along the blade toward the tip. The oval opening in the plywood was adjusted until the plywood could be slid along the propeller blade to a point about ten centimetres above the ragged root end of the blade. This determined how deep the propeller blade would be inserted into the opening in the stand.

Once the cross-sectional profile shape of the propeller blade had been completed in plywood, the shape of the opening was transferred to the wooden blocks placed side by side for the stand. The excess was cut away from the four blocks with a band saw, forming an oval opening in the middle of the blocks corresponding to the cross-section of the propeller blade. The opening still had to be adjusted several times before the edges of the opening pressed tightly against the sides of the propeller blade. It was time to assemble the propeller-blade stand.

First, the two lowest wooden pieces were screwed onto the metal base of the memorial. After that, the lower layer of the blocks, shaped according to the propeller-blade profile, was fastened on top of them with screws. It was then checked that the blade fitted well into the opening. Assembly of the stand continued by fastening into place the upper pair of blocks with the opening. It was found that the oval opening still needed to be adjusted in these parts so that the propeller blade would press tightly into the opening in the stand. After adjustment, the contact surface between the blade and the stand was made tight, and the blade could be pressed to exactly the right depth. Thus, the stand parts with openings were ready and could be fastened with screws to each other and to the lowest part of the stand. Stainless-steel screws were used.

Eventually the propeller blade could now be slid into the opening in the stand and screwed into place. The seam between the propeller blade and the stand was sealed with black Casco Multitech sealant. As the final restoration task, the surface of the propeller blade was lightly sanded with 240-grit sandpaper and varnished with clear Isotrol. This treatment protects the propeller blade from dirt and UV radiation.

Once the bronze plaque attached to the propeller blade had been screwed back into its original position, the restoration of the propeller-blade memorial on Heikki Marklund’s grave had been completed by the Tuesday Club.

Photos: Lassi karivalo

Translation to English: Erja Reinikainen