Does anyone who uses a pressure-washer around the house or garden know if it has a bad effect upon wood which has been treated with wood preservative? I have a lot of horizontal and vertical wood around this new house and garden here and I am inclined to apply a few coats of wood preservative - as soon as the weather allows. However, after the autumn rains and leaf-fall I expect there will be a build-up of dirt/grime/slime, in corners particularly, and so I am wondering if using a pressure-washer will remove a noticeable degree of the preservative in such places . . . in which case it would be sensible not to go buying us a pressure-washer!
First of all, if the timber is presure treated e.g. Tanalised then nothing can remove it.
If its an after applied product it will either soak into the timber or form a coating on the surface. In the former case it won't be removed by the pressure washer, in the latter anything loose or flakey will be removed providing an ideal (when dry) base for recoating.
Standard practice in Germany & Denmark (the birthplace's of the pressure washer) is to use one prior to exterior painting.
Eddy, Dave is quite right. If it is tanalised, you can do what you like but if it is double vacuum treated with an OS process there will be leeching from the outer surface of the wood which will happen anyway with the weather. All you will do is increase it. If it is aquavac double vacuum treated I THINK but am not certain that the level of penetration of active ingredient is a bit less than with OS and so a greater percentage of active ingredient will be removed. If the purpose of the treatment is to preserve the wood I would recommend you not pressure washing but after you have applied the preservative to apply a surface coating with a water repellent. This should protect the actual wood and act as a sacrifical layer which can be re-applied every couple of years or so as it chalks away. Application is easy with spray or brush. If it were my house and the wood was a suitable timber for the application (say Scots pine) I would carefully remove the cladding and take it as it is (cut to size) to my nearest double vacuum treatment plant for treatment. I would slip the operator a tenner to leave it in the bottom of the machine for a day as he did his normal loads. At the end of the day, wrap it in suitable protective polythene to protect yourself from the carrier fluid smells and put it on the back of a pick up or lorry or top of a car if suitable, let it "dry" for a couple of days and then put it all back. Then I would paint it with Saddolins. I have done this with a decorative garden fence 20 years ago and it is in pristine condition with a coat needed every 3 years or so. My neighbour copied my style of fence but neglected to do the treatment and is now on his second fence. I suspect this will not appeal! so if you are to retain timber in situ which is not pressure treated and you wish to apply a preservative in situ to the timber then I suggest that you use a combination insecticide/fungicide suitable for the species of timber and its porosity. I can advise if you tell me what the timber is and whether there is much sapwood in it. Chris
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